Multiengine Add-On Oral Exam

• No knowledge (written) test. § 61.63(c) requires only training, an endorsement, and a practical test for an additional class rating.
• A logbook endorsement from an authorized instructor certifying you received training and are proficient in the areas of operation that apply.
• A practical test at the level of the certificate you already hold - a private pilot tests to the Private ACS, a commercial pilot to the Commercial ACS.
• No minimum flight hour requirement for the class add-on itself. Proficiency is the standard, not a number.

• § 61.63(c) requires only training, an endorsement, and a practical test for an additional class rating, so there's nothing to screen your knowledge before you meet the examiner.
• That pushes all of the knowledge evaluation into the oral. Expect it to be longer and deeper than the add-on's short flight portion suggests.
• The weight lands on the topics unique to twins: V_MC and everything that moves it, the critical engine, zero sideslip, one-engine-inoperative (OEI) performance, and systems.

Less than most people expect. The Tasks are identical. Both the Private ACS and the Commercial ACS contain Area of Operation X, Multiengine Operations, with the same four Tasks:

• A - Maneuvering with One Engine Inoperative
• B - V_MC Demonstration
• C - One Engine Inoperative (Simulated), solely by reference to instruments, in straight-and-level flight and turns
• D - Instrument Approach and Landing with an Inoperative Engine (Simulated), by reference to instruments

Tasks C and D are conditional in both ACSs. They don't apply if you hold no instrument airplane rating, or if you've already shown multiengine instrument proficiency. Skip them and the certificate carries an "Airplane Multiengine VFR Only" limitation, removed later by flying those two Tasks in an airplane with a published V_MC.

What changes between the two levels is the tolerance. During the V_MC demo recovery you must maintain V_SSE/V_YSE:

• Private - +10/-5 kt
• Commercial - ±5 kt

Beyond Area X, what else gets tested depends on the certificate you already hold. Adding AMEL to a certificate you already hold at that level means a practical test on the areas that apply to the new class rating, not the full commercial curriculum over again.

• You receive it when you complete the AMEL practical test in a multiengine airplane that does not have a manufacturer's published V_MC - for example a Cessna 337, whose engines are in line with the fuselage and produce no asymmetric thrust.
• The published V_MC appears on the type certificate data sheet (TCDS) or in the AFM. That's the actual test, not simply where the engines are mounted.
• It restricts you to multiengine airplanes that don't produce asymmetric thrust.
• To remove it, take a practical test on the multiengine Tasks in a multiengine airplane that does have a published V_MC.

Only if you demonstrated instrument proficiency in a multiengine airplane on the checkride.

• The instrument rating itself is issued for the category (airplane), not the class, so nothing about the rating stops you.
• But per the ACS: if you hold both a single- and multiengine rating and have not demonstrated instrument proficiency in a multiengine airplane, your certificate must bear a limitation that multiengine flight is permitted in VFR conditions only.
• That's what ACS Tasks X.C and X.D exist for. They aren't required if you already demonstrated instrument proficiency in a multi, or if you don't hold an instrument airplane rating at all.
• Removing the limitation later requires testing those Tasks in an airplane with a manufacturer's published V_MC.
• Currency is a separate question from privileges. Instrument currency under § 61.57(c) is by category, so approaches flown in a single count toward currency for the multi and vice versa. That does not lift a VFR-only limitation - if your certificate carries one, being instrument current does not authorize you to fly the twin IFR.

These are separate from the class rating, and you may need both:

• Complex (§ 61.31(e)) - retractable gear, flaps, and a controllable-pitch propeller. Nearly every light twin qualifies.
• High performance (§ 61.31(f)) - an engine of more than 200 horsepower. Note this is measured per engine, not by total installed horsepower.

A common trainer such as a Seminole or Duchess is complex but not high performance, because each engine is 180 hp. A Baron or a 310 is both.

Both are one-time endorsements, not recurring currency.

No, currency applies to the category and class, meaning you're only current to take passengers up in a multi-engine airplane.

• Hold a commercial or ATP certificate with an airplane category and multiengine class rating.
• Hold an instrument rating, or ATP instrument privileges. This is required for the multiengine instructor rating itself, not only if you plan to teach instruments.
• You do not need an existing CFI. The multiengine rating can be your initial flight instructor certificate. The spin training endorsement still applies, and it has to be done in an airplane certificated for spins, which no twin is.
• Log at least 15 hours of PIC time in multiengine airplanes.
• Pass a practical test in a multiengine airplane, demonstrating and simultaneously explaining the multiengine maneuvers to instructor standards. It is normally flown from the right seat, since that is where you will be instructing from.
• Adding the rating to a CFI you already hold skips the fundamentals of instructing knowledge test, but every other eligibility requirement still applies.

Roughly 80% of your climb performance, not 50%.

• You lose half your power, but climb performance depends on excess power - what's left over after overcoming drag. Most of the remaining engine's output is consumed just holding level flight.
• On top of that, the dead engine adds drag, and the control inputs needed to stop the yaw add more.
• A typical light twin at gross weight on a warm day may climb only 100-200 fpm on one engine, and some can't climb at all.

The practical conclusion: a light twin's second engine buys you time and options, not guaranteed climb. Treat single-engine climb as something you verify in the charts before takeoff, not something you assume.

• In normal two-engine flight you have a large surplus of thrust over drag, and that surplus is what climbs the airplane. Adding drag just eats into a healthy margin.
• With one engine out, the surplus is nearly gone. Every additional unit of drag comes straight out of climb rate.
• A windmilling propeller, extended gear, extended flaps, or flying with a sideslip can each individually erase what little climb you have.

This is why the OEI flow is fundamentally about drag reduction, and why the cleanup happens before you try to troubleshoot anything.

• Each propeller blows high-velocity air over the section of wing directly behind it, so that part of the wing produces substantially more lift than the rest.
• With both engines running, the effect is symmetric and you never notice it.
• When one engine quits, the lift behind the dead engine drops away while the operating side keeps its accelerated slipstream. The result is a rolling moment toward the dead engine, on top of the yaw from asymmetric thrust.
• It's also one of the four factors that make one engine critical, and P-factor is what links the two. At a positive angle of attack the descending blade produces more thrust, so it accelerates more air over the wing behind it. On two clockwise-turning propellers the descending blade of each is on its right side, which displaces the center of the added lift to the right of each engine's centerline.
• That displacement is outboard on the right engine and inboard on the left. So losing the left engine leaves the right engine producing its extra lift at a longer arm from the airplane's longitudinal axis, and the rolling moment toward the dead engine is stronger. Losing the right engine leaves the left engine working at a shorter arm, and the roll is weaker - which is one of the four reasons the left engine is critical.

• Service ceiling - The altitude at which the airplane can no longer climb at more than 100 fpm. In a twin, that is with both engines operating. The figures are given for a specific configuration.
• Absolute ceiling - The altitude at which the airplane can no longer climb at all. Rate of climb is zero, and V_X and V_Y have converged to a single speed.

The single-engine versions use the same idea with one engine inoperative and its propeller feathered, but the service-ceiling climb rate is different. The single-engine service ceiling is where the airplane can no longer climb at 50 fpm in smooth air, with one engine feathered, at maximum certificated takeoff weight. In real conditions it may not hold altitude even there. The single-engine absolute ceiling is where OEI climb stops altogether. Above that absolute ceiling, the AFH says V_YSE gives the minimum rate of sink.

The 100/50 split is a favorite oral question, and swapping the two numbers is the usual way to miss it.

• The density altitude at which the airplane, with the critical engine inoperative and its propeller feathered, can still climb at 50 fpm at V_YSE.
• It is far lower than the all-engines service ceiling - often only a few thousand feet, and on a hot day at a high field it can be below the terrain around you.
• This is the number that answers the real question after an engine failure: can I climb, hold altitude, or only slow my descent?
• It's also why a drift-down plan matters - but get the trigger right. Between this altitude and the single-engine absolute ceiling the airplane still climbs, just at less than 50 fpm. Only above the absolute ceiling does a failure mean losing altitude. Plan on the service ceiling anyway: the AFH cautions that engine and propeller wear, turbulence, and pilot technique mean the airplane may not hold altitude even at the published single-engine ceiling.

• No. Normal-category multiengine airplanes are not approved for spins and have no published spin recovery procedure, because no spin recovery testing is required for certification.
• The dangerous combination is asymmetric thrust plus a stall. Yaw at the stall is exactly what starts a spin, and a twin gives you a powerful yawing moment for free the moment an engine fails.
• Recovery in a twin is often unreliable, and altitude loss can be extreme.

The defense is procedural, not a recovery technique: never let the airplane get slow with asymmetric power. That is the reason you recover a V_MC demonstration at the first indication rather than riding it to the stall.

Which one comes first determines what the airplane does when you get slow with an engine out.

• If V_S is reached first (V_MC is below the stall), the airplane reaches the stall with directional control intact. Better than the alternative, but not an ordinary stall - stalling with asymmetric thrust is the classic spin entry. Recover by reducing power on the operating engine to cut the asymmetry and lowering the angle of attack at the first indication.
• If V_MC is reached first (V_MC is above the stall), you lose directional control while the wings are still flying. The airplane yaws and rolls toward the dead engine, and at low altitude that is unrecoverable.

The second case is the one red line exists for, and it's why red line matters more than the stall strip in a twin. In a normally aspirated twin, V_MC falls with altitude while indicated stall speed doesn't, so the relationship flips somewhere in the climb.

• Red radial line - V_MC. The minimum control speed with the critical engine inoperative, as determined during certification.
• Blue radial line - V_YSE. The best rate of climb speed with one engine inoperative.

Both are single fixed marks, but the speeds they represent move with configuration, weight, CG, and altitude. Treat them as reference points, not guarantees.

The rest of the markings match any airplane: white arc for the flap operating range, green arc for normal operating range, yellow arc for caution, and a red line at V_NE.

• V_YSE is the best rate of climb speed with one engine inoperative - the speed that gives the most altitude gain per unit of time. Above the single-engine absolute ceiling, where climb is no longer possible at all, the AFH says V_YSE also yields the minimum rate of sink.
• It is marked with a blue radial line, because it's the single most important speed to be at after an engine failure.
• It delivers the best climb only with the airplane cleaned up and in zero sideslip. V_YSE with the gear down and a windmilling propeller still won't climb.
• Published V_YSE is for maximum gross weight; the actual speed decreases slightly as weight decreases.

• V_XSE is the best angle of climb speed with one engine inoperative - the most altitude gained per unit of horizontal distance.
• It's slower than V_YSE and is not marked on the airspeed indicator.
• Use it only when you need to clear an obstacle. The ACS wording for an engine failure with obstructions present is to establish V_XSE, or V_MC + 5 kt, whichever is higher.
• Once the obstacle is no longer a factor, accelerate to V_YSE. V_XSE buys angle at the cost of time spent low and slow, closer to V_MC.

• Default to V_YSE. It's the blue line, it's marked, and it gives the best single-engine rate of climb - and, per the AFH, the minimum rate of sink once you are above the single-engine absolute ceiling and climb is off the table.
• Use V_XSE only when an obstacle is the immediate problem - rising terrain off the departure end, trees, a tower. Per the ACS, establish V_XSE or V_MC + 5 kt, whichever is higher.
• Return to V_YSE as soon as the obstacle is behind you.

The tradeoff: V_XSE is slower, which means less margin above V_MC and more time spent in the region where a mishandled control input turns into loss of control.

• V_SSE is the safe, intentional one-engine-inoperative speed - the minimum speed at which an instructor or examiner may intentionally render an engine inoperative in flight.
• It exists purely for training safety. It is set comfortably above V_MC so that a deliberately induced failure doesn't put the airplane near loss of directional control.
• It is published in the AFM but is not marked on the airspeed indicator.
• It says nothing about how the airplane behaves in a real engine failure, which doesn't wait for you to be above any particular speed.

V_MC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is still possible to maintain control of the airplane with that engine inoperative and then maintain straight flight at the same speed with a bank angle of not more than 5°.

Two things students routinely miss:

• It's about directional control, not performance. Being above V_MC says nothing about whether the airplane will climb.
• The red line is one number determined under one specific set of certification conditions. Actual V_MC on any given day is usually lower, but under the wrong conditions it can be higher than the mark on the dial.

• Use the AFM's published rotation and lift-off speeds. Where the AFM doesn't publish them, the AFH calls for a minimum of V_MC plus 5 knots as V_R - a margin above the red line, not the red line itself.
• After lift-off, with both engines running, the AFH has you accelerate to V_Y, the all-engine best rate of climb speed, and hold it to a safe single-engine maneuvering altitude. V_YSE is the gate for the gear - the AFH's general recommendation is gear up no later than V_YSE - and it's the speed you go to if an engine actually quits, not the normal two-engine climb speed.
• Rotating early puts you airborne at or below V_MC. If an engine fails there, you have no ability to maintain directional control, and the airplane will roll toward the dead engine with the ground very close.
• Accelerating on the runway costs a little distance but means that by the time you are airborne, an engine failure is a controllable event.

This is the practical reason many light twin takeoff briefings are built around a hard rule: still on the runway below that speed means abort.

No. The part 25 balanced field concept - and the guaranteed stop-or-go performance behind V₁ - doesn't exist for a normal-category light twin.

• A part 25 airplane is certified to lose an engine at V₁ and still either stop in the remaining runway or continue the takeoff and climb on one engine. That guaranteed performance is what makes a single decision speed meaningful.
• A light twin has no such guarantee. It may not be able to climb at all on one engine at that weight, altitude, and temperature.
• What you have instead is whatever performance data your AFM publishes - often accelerate-stop and accelerate-go distances, often only takeoff and single-engine climb charts - plus a decision point that you choose and brief before every takeoff.

So the honest answer to an examiner is that a light twin has no V₁ in the part 25 sense, and that the absence of the guarantee behind it is exactly why the takeoff briefing matters so much. If your AFM does publish a V₁ or V₂ - some part 23 commuter-category and turboprop airplanes do - fly the AFM's number. What that number lacks is the certified stop-or-go performance standing behind a part 25 V₁.

Legacy § 23.149 set the conditions, deliberately the most unfavorable realistic combination. What the rule itself says:

• Bank angle of not more than 5° toward the operating engine, holding straight flight at the same speed after the critical engine is suddenly made inoperative - (a).
• V_MC for takeoff may not exceed 1.2 V_S1, with V_S1 at maximum takeoff weight - (b).
• Most unfavorable weight and center of gravity, airborne with ground effect negligible - (b). For a light twin the most unfavorable CG is the aft limit, because it shortens the rudder arm.
• Maximum available takeoff power initially on each engine - (b)(1).
• Trimmed for takeoff - (b)(2).
• Flaps in the takeoff position - (b)(3).
• Landing gear retracted - (b)(4).
• All propeller controls in the recommended takeoff position throughout - (b)(5).
• Rudder pedal force not exceeding 150 lb, and no need to reduce power on the operating engine - (e).
• No dangerous attitude, and it must be possible to prevent a heading change of more than 20° - (e).

Two conditions people recite that the rule doesn't name explicitly. Both still come from it:

• Windmilling propeller - (b)(5) keeps the propeller controls in the recommended takeoff position, and on a twin without autofeather that leaves the failed propeller windmilling. An airplane certified with autofeather is a different case - know which one you fly.
• Cowl flaps set for takeoff - the AFH reads the (b)(3) takeoff flap condition as covering wing flaps and cowl flaps.

Paragraph (c) adds the landing configuration, but exempts reciprocating airplanes of 6,000 lb or less, which is every piston trainer.

No. An airplane's certification basis is fixed at the time of type certification. The 2017 rewrite of part 23 is not retroactive and changed nothing about any existing airplane's V_MC. The red line on a Seminole, Seneca, Duchess, or Baron was determined under the legacy rule, so the legacy conditions are the ones that literally describe the airplane you fly. The AFH and the ACS still teach them.

What actually changed:

• The 2017 rewrite replaced part 23's prescriptive standards with performance-based ones. § 23.149 no longer exists, which is why sources cite it by its last published edition.
• Its replacement, § 23.2135(c), still defines the speed: "V_MC is the calibrated airspeed at which, following the sudden critical loss of thrust, it is possible to maintain control of the airplane. For multiengine airplanes, the applicant must determine V_MC, if applicable, for the most critical configurations used in takeoff and landing operations."
• What it no longer does is state the numbers. No 5° bank, no 150 lb rudder force, no 20° heading change, no 1.2 V_S1 cap. Those now live in the accepted means of compliance an applicant uses, rather than in the CFR itself.

So quote the § 23.149 conditions with confidence, and be able to add that they come from the version of part 23 your airplane was certified under rather than from today's CFR.

No. The red line is one number determined under one specific set of certification conditions, and your actual V_MC moves with conditions.

• Most of the time your actual V_MC is lower than red line, because you are rarely at the most unfavorable weight, CG, and configuration all at once.
• But it can be higher than red line when you are outside what certification assumed. The big one is failing to bank into the operating engine - wings level, the real loss of control can come almost 20 kt above the published number.
• Other ways to get there: operating outside the approved envelope (aft of the CG limit), flying clean when certification used the takeoff flap setting, or a propeller that fails to feather when certification assumed an automatic feathering device.
• A related trap that isn't the same thing: certification allowed up to 150 lb of rudder force. Don't apply what's available and you lose control above the airplane's V_MC - which doesn't raise the aerodynamic V_MC, only the speed at which you run out of control.
• What does not belong on that list: a tired operating engine. Less power means less asymmetric thrust, so V_MC goes down, not up - a worn engine costs you climb, not directional control.
• Nor an approved aft CG, or a windmilling propeller on a twin whose red line was established with one. Those are the conditions § 23.149(b) already assumes, not departures from them. Know your own airplane, though: where certification assumed automatic feathering, a propeller that windmills instead is a departure.

Treating red line as a hard floor is the mistake. Being 5 kt above the mark is not the same as having control margin.

It is the largest single lever you have, and the only one you control directly in the moment.

• Banking toward the operating engine tilts the lift vector, and its horizontal component helps the rudder oppose the yaw from asymmetric thrust.
• Certification allows a bank of not more than 5°. Flying wings level instead of banked raises V_MC dramatically - the AFH says V_MC may increase more than 3 knots for each degree of bank reduction between 5° and wings level, which is why it also says loss of directional control can come almost 20 knots above the published number with the wings held level.
• Banking beyond about 5° keeps lowering V_MC but degrades climb performance and moves you away from zero sideslip, so it isn't free.

This is why "bank into the good engine" is the reflex being trained, not an optional refinement.

More power raises V_MC. It is the most direct relationship of any factor: the yaw you are fighting comes from thrust on one side, so more thrust means a larger yawing moment and a higher speed needed to generate the rudder force that opposes it.

• Certification uses maximum available takeoff power initially on each engine - § 23.149(b)(1) - because that is the worst case.
• The rule also requires that it not be necessary to reduce power on the operating engine to keep control at V_MC - (e). Throttling back is not an allowed part of the test.
• It follows that reducing power on the good engine removes the yaw at its source - which is why power comes off, not on, in a V_MC recovery.
• This is also the mechanism behind the altitude effect: a normally aspirated engine cannot make takeoff power up high, so the asymmetric thrust weakens and V_MC falls.

The corollary: less power means less asymmetric thrust, so a tired or partially failed operating engine leaves you with a lower V_MC, not a higher one.

An aft CG raises V_MC, which is why certification uses the most unfavorable (aft) CG.

• The rudder generates a yawing moment equal to force times arm, and that arm is the distance from the CG to the rudder.
• Moving the CG aft shortens the arm, so the same rudder deflection produces less corrective yawing moment.
• With less authority available to oppose the asymmetric thrust, you need more airflow over the rudder to do the job - a higher speed.

A forward CG has the opposite effect and lowers V_MC. It's one of the few cases where loading the airplane forward is a controllability benefit, not just a stability one.

Heavier is lower. This one is counterintuitive and gets asked constantly.

• When you bank into the operating engine, the horizontal component of lift is what helps the rudder fight the yaw.
• At a given bank angle, a heavier airplane is producing more total lift, so that horizontal component is larger and does more of the work.
• More help from the lift vector means you need less help from airflow over the rudder, so V_MC goes down.

That's why certification specifies the most unfavorable weight. Be careful not to confuse this with performance: the heavier airplane has a lower V_MC but worse single-engine climb.

V_MC decreases with altitude in a normally aspirated twin.

• The operating engine loses power as density altitude rises, so the asymmetric thrust producing the yaw gets weaker.
• Less yaw to oppose means less rudder authority required, which means a lower speed will do.

Two important qualifiers:

• Indicated stall speed does not change with altitude, so the gap between the two closes and eventually reverses.
• A turbocharged twin holds full rated power up to its critical altitude, so its V_MC may stay high well into the climb - and can remain above the stall speed where a normally aspirated twin's would not.

Extending the landing gear lowers V_MC. The gear adds keel area and drag, increasing directional stability - the fuselage resists being yawed out of line, so less rudder is needed to balance the asymmetric thrust. Certification uses gear retracted because that's the more unfavorable case.

Extending flaps also lowers V_MC, slightly, for two reasons:

• Lower angle of attack. Flaps let the wing make the same lift at a lower AoA, and the asymmetry you're fighting is largely P-factor, which grows with angle of attack. Less AoA means a smaller yawing moment to balance, so less rudder, so a lower V_MC.
• Flap drag in the slipstream. The flap section behind the operating engine sits in that engine's accelerated slipstream and makes more drag than the same section on the dead side. That small asymmetry pulls the nose back toward the operating engine, opposing the yaw.

The flap effect is small and airplane-specific, which is why certification uses the takeoff position rather than clean. Note the AFH lists takeoff flaps as a condition without explaining the mechanism - the reasoning above is aerodynamic, not a quotable handbook passage.

Don't turn any of this into a technique. Lowering the gear to reduce V_MC trades a control benefit for a large drag penalty and destroys whatever single-engine climb you had - a good exam answer about aerodynamics, and a bad plan in the airplane.

• A windmilling propeller produces a large amount of drag well out on the wing, adding to the yawing moment the rudder must oppose. That raises V_MC.
• A feathered propeller has its blades edge-on to the airflow, producing minimal drag, which lowers V_MC and substantially improves climb.

Certification assumes the propeller is in the position it automatically assumes when the engine fails - for most training twins, windmilling. That's the conservative case, and it's why feathering promptly is worth so much: it improves both controllability and performance at the same time.

• In a normally aspirated twin, V_MC falls with density altitude as the operating engine loses power, while indicated stall speed stays essentially constant. A turbocharged twin holds full asymmetric thrust to critical altitude, so its V_MC need not fall this way.
• Low down, V_MC may be above the stall speed - so a slowing airplane loses directional control first.
• High up, V_MC drops below the stall speed - so the airplane stalls before it reaches V_MC. Both the ACS and the AFH say so for normally aspirated engines: at some altitude the two speeds are the same.

This matters in two directions:

• It's why the ACS has you recover a V_MC demonstration at the first indication of loss of directional control, stall warning, or buffet. At altitude, the stall arrives first, and a stall with asymmetric thrust can rapidly develop into a spin.
• It's why a demonstration at a safe altitude can never show you the low-altitude case, which is the one that actually kills people.

SMACFUM is the list of conditions your airplane's published V_MC was measured under. Every letter but U is set to make V_MC as high as possible - which is why the red line is a worst case rather than a number you will see in normal flight.

• Because every row but U is set against you, your actual V_MC is usually lower than the red line.
• It can sit above the red line too. Giving up the bank is the big one. So is anything outside what certification assumed - an aft CG beyond the approved envelope, or a propeller that windmills where the airplane was certified with autofeather.
• Density altitude assumes a normally aspirated engine. A turbocharged twin holds rated power to its critical altitude, so its V_MC stays high well into the climb - above that altitude it falls off like any other.
• This is a mnemonic for the factors that move V_MC - not the certification standards. § 23.149 also fixes trim and out of ground effect, and sets criteria the airplane had to meet: a 150 lb rudder pedal force limit, no more than 20° of heading change, and V_MC no greater than 1.2 V_S1. Those are pass/fail standards rather than things that move the speed.

The engine whose failure would most adversely affect the performance or handling qualities of the airplane.

• In a conventional twin with both propellers turning clockwise as seen from the cockpit, the critical engine is the left one.
• "Critical" is about the remaining engine's ability to yaw the airplane. Losing the left engine leaves the right engine producing the larger yawing moment, so more rudder is needed and V_MC is higher.
• If the airplane has counter-rotating propellers, there is no critical engine.

PAST is the usual mnemonic, not FAA language.

• P-factor - At a positive angle of attack the descending blade produces more thrust. On a conventional twin, both propellers turn clockwise, so that blade is on the right of each disc and both thrust lines shift right. On the left engine that shift is inboard, toward the fuselage; on the right engine it is outboard. The right engine ends up with the longer arm and produces a stronger yawing moment.
• Accelerated slipstream - Each propeller's high-velocity air adds lift on the wing behind it, centered on that same displaced thrust line. So it too sits farther out on the right engine, giving a longer rolling arm.
• Spiraling slipstream - The corkscrew off the left propeller wraps around the fuselage and strikes the left side of the vertical stabilizer, countering the yaw when the right engine fails. The right propeller's corkscrew passes outboard of the tail, so there is no matching help to lose.
• Torque - Due to Newton's third law, in a conventional twin with both propellers rotating clockwise, the aircraft rolls in the opposite direction (counter-clockwise), which produces a left roll. When you lose any engine, asymmetric thrust creates a rolling and yawing motion towards the dead engine. With the left engine out, torque adds to the existing roll toward the dead engine created by asymmetric thrust, and with the right engine out, torque opposes it.

All four point the same way: losing the left engine on a conventional twin with clockwise-rotating props is worse.

Think of it as thrust arms about the center of gravity.

• Because of P-factor, each engine's effective thrust line sits slightly to the right of its physical centerline.
• If the right engine fails, the operating left engine's thrust line has been shifted toward the fuselage - a shorter arm - so it produces a smaller yawing moment. Easier to control, lower V_MC.
• If the left engine fails, the operating right engine's thrust line has been shifted away from the fuselage - a longer arm - so it produces a larger yawing moment. Harder to control, higher V_MC.

Since losing the left engine leaves you fighting the bigger moment, the left engine is critical. Spiraling slipstream, accelerated slipstream, and torque all reinforce the same conclusion.

• The propellers turn in opposite directions, with the descending blade of each on the inboard side. That pulls each engine's thrust line toward the fuselage and makes the two moment arms equal.
• Both engines then produce the same yawing moment when the other fails, so there is no critical engine. A Seminole, a Duchess, and a Seneca are common examples.
• With both engines running, torque and spiraling slipstream effects also cancel between them.

Two things not to over-claim: it does not mean the airplane has no V_MC, and it does not mean an engine failure is benign. You still get a large yawing moment, still need rudder and bank, and still fly the full engine-failure flow. Nor do torque, P-factor, and slipstream disappear once an engine quits - the operating engine still produces all three. Counter-rotation equalizes the two failure cases; it doesn't remove the effects. It just means it doesn't matter which one quits.

The combination of bank and rudder that makes the airplane fly straight through the air with the fuselage aligned to the relative wind, producing the least possible drag with one engine inoperative.

• With asymmetric thrust, you need rudder to stop the yaw. Rudder alone leaves the airplane flying slightly sideways through the air, which is drag you cannot afford.
• Adding a small bank toward the operating engine lets the horizontal component of lift do part of the work, so less rudder is needed and the fuselage lines up with the airflow.
• It is the configuration in which published single-engine climb performance was actually measured. Fly it any other way and you will not see book numbers.

• Bank approximately 2° toward the operating engine. The precise angle varies by model from 1.5° to 2.5° - the 5° certification limit is not a zero-sideslip figure and does not establish it.
• Hold enough rudder toward the operating engine to stop the yaw.
• The inclinometer ball ends up one-third to one-half of a ball width displaced toward the operating engine - not centered.

So the picture is: slight bank into the good engine, ball split toward the good engine, heading steady. A yaw string will show you directly whether the fuselage is aligned with the airflow - the AFH recommends one for exactly this - but it won't hand you the bank-and-rudder combination or your airplane's performance optimum. The ball alone certainly won't; the combination is what matters.

Raise the dead: the dead engine's wing comes up.

Although it feels correct, it worsens your climb rate.

• With wings level and the ball centered, the rudder is doing all the work of opposing the yaw, and the airplane ends up slipping through the air toward the inoperative engine.
• The fuselage is presented at an angle to the relative wind, which adds substantial parasite drag at exactly the moment you have no surplus power.
• Zero sideslip is what produces the best rate of climb - or the least rate of descent. In a light twin that margin is thin enough that giving up part of it can be the entire difference between climbing and not.
• It also raises V_MC, because you have given up the help of the lift vector's horizontal component.

Wings level is the single most common way trained pilots quietly throw away their single-engine performance.

• Holding heading on ailerons alone takes 8-10° of bank toward the operating engine (AFH Fig 13-16).
• With no rudder input, the ball is displaced well toward the operating engine - far more than the third to half a ball of zero sideslip.
• The airplane is left in a large sideslip toward the operating engine, and climb performance is greatly reduced.
• The risk of losing directional control is high enough that instructors should not normally demonstrate it.

Wings level and excessive bank bracket zero sideslip from either side: one slips toward the dead engine, the other toward the good one. Wings level is the moderate error; excessive bank is the severe one.

Why bank and rudder together produce zero sideslip

• Left engine out: the right engine's thrust yaws the nose toward the dead engine. Right rudder stops the yaw.
• But the rudder is a lifting surface. The side force it produces on the tail acts toward the dead engine, and with the wings level nothing opposes it - so the airplane slips through the air, fuselage skewed to the relative wind.
• Bank ~2° toward the operating engine. The lift vector tilts, and its horizontal component acts toward the good engine, opposing the rudder's side force.
• With the two in balance, the airplane no longer has to slip to make up the difference. The fuselage aligns with the relative wind: zero sideslip.

Why that leaves the ball off center

• The horizontal component of lift is what normally turns an airplane. Here it is fully committed to opposing the rudder, so the net sideways force is zero - the flight path stays straight and the heading holds.
• In a normal coordinated turn the ball centers because the bank produces a turn, and the turn's inertia pushes the ball outboard by exactly as much as gravity pulls it toward the low wing.
• In zero sideslip there is no turn, so nothing offsets gravity. The ball responds to gravity alone and settles toward the low wing - one-third to one-half a ball width toward the operating engine. Its displacement is really just reading your bank angle.

Why this contradicts the single

• In a single, a slip (ball toward the low wing) and a skid (ball toward the high wing) are the same thing in opposite directions - both are sideslip, and both show on the ball.
• What a single doesn't have is a standing sideways force. The rudder can certainly make one - a forward slip is exactly that - but it is a force you are choosing to hold, and releasing it removes the force and the sideslip together. Centering the ball and zeroing the sideslip normally coincide, which is why "step on the ball" works in either direction.
• With an engine out, the rudder you hold is opposing a yawing moment from thrust, not from the relative wind. It stays there whether or not the fuselage is aligned, and the ball - which only sees the sum of the forces - cannot tell the two sources apart.
• So "balanced" now has two solutions: let the air balance the rudder, which takes a sideslip, or let the horizontal component of lift balance it, which does not. Only the second is zero sideslip.

In a single, a centered ball means no sideslip. In a twin with an engine inoperative, it means no bank - and with rudder held in, no bank means you are slipping. Chasing the ball back to center from a correct 2° of bank takes still more rudder, restores the sideslip, and turns you instead of holding heading.

• Apply rudder immediately and firmly. The initial input is large - stopping the yaw is the first priority, before anything else.
• Once the airplane is stabilized in zero sideslip, trim the rudder to relieve the pressure. Holding a heavy leg load for a long single-engine approach is how mistakes creep in.
• Retrim as airspeed and power change, since the required rudder varies with both.
• Be ready to remove that trim during recovery or a change in configuration; rudder trim held into a power reduction can produce yaw in the opposite direction.

The workload argument matters: an untrimmed leg gets tired, and a tired leg relaxes at exactly the wrong moment on short final.

They are separate questions, and confusing them is dangerous.

• Controllability - Can you keep the airplane pointed where you want? This is the V_MC question. Its answer is airspeed, bank, and rudder.
• Performance - Can you climb, hold altitude, or only slow the descent? This is the single-engine climb question. Its answer is weight, density altitude, configuration, and drag.

Being above V_MC tells you only that you can steer. Many light twins are perfectly controllable while descending steadily into terrain.

The practical consequence: after the failure you solve control first (pitch for V_YSE, bank into the good engine, stop the yaw), then solve performance (clean up the drag, feather), then decide where the airplane can actually go.

• Published single-engine climb assumes the best case: critical engine feathered, gear and flaps up, zero sideslip, V_YSE, maximum power on the good engine, and a new airplane flown by a test pilot.
• Real numbers in a light twin at gross on a warm day are commonly 100-200 fpm, and can be zero or negative.
• Every departure from that ideal costs you: a windmilling prop, gear down, flaps out, or a sideslip can each individually consume all of it.

The planning discipline is to look up single-engine climb for today's weight, pressure altitude, and temperature before you take off, and to know your single-engine service ceiling. If the chart says you can't climb, the airplane will not surprise you by climbing.

Roughly in order of magnitude for a typical light twin:

1. Windmilling propeller - The single largest item, and the reason feathering is the highest-value action available to you.
2. Extended landing gear - Large parasite drag, and usually the easiest thing to fix.
3. Extended flaps - Significant beyond the takeoff setting.
4. Sideslip - Flying wings level or with the ball forced center.
5. Open cowl flaps - Small individually, and not a free cleanup: cowl flaps are engine-temperature control, and the operating engine at climb power may need them open. Set them as the AFM directs, not reflexively closed.

The order is why the OEI flow is about drag reduction before it's about troubleshooting. You buy back climb in the order above, then worry about why the engine quit.

Control first, then drag, then diagnosis - the order the AFH says most AFM/POH checklists use. Your airplane's checklist is the authority; some retract the gear before the flaps.

Control

• Pitch for V_YSE (blue line)
• Rudder to stop the yaw, bank ~2° into the operating engine (zero sideslip)

Configure / reduce drag

• Mixtures forward
• Props forward
• Throttles forward
• Flaps up
• Gear up
• Cowl flaps as required

Identify, verify, feather

• Identify - "Dead foot, dead engine," from the control inputs, not the gauges
• Verify - Slowly retard the suspect throttle. No change in performance is the verification
• Feather - Corresponding propeller control fully aft

Then secure the engine, declare as appropriate, and fly the airplane to a landing. Finish with the printed checklist, deliberately - other than closing the failed engine's cowl flap, none of the remaining items affects climb performance.

The flow includes flaps and gear even when they're already up. A memory item either initiates an action or confirms a condition, and the same flow has to work for a failure during a go-around.

• It tells you the highest altitude the airplane can still climb at 50 fpm with one engine feathered - in practice, the highest altitude you can count on holding. Above it the airplane still climbs, just at less than 50 fpm, up to the single-engine absolute ceiling where climb is no longer possible. Above that, a failure means a drift down.
• Over terrain, that turns into a screening question: is the single-engine service ceiling above the highest terrain and obstacles along your route, with margin? Treat it as a screen, not a clearance calculation - the real answer comes from the AFM single-engine climb data at the weight, temperature, and altitude you'll actually be flying.
• If it isn't, you need a different route, a lower weight, a cooler time of day, or an honest acceptance that an engine failure means an off-airport landing.
• It also shapes your escape plan - knowing which direction leads to lower terrain matters far more in a twin that can only descend slowly than in one that can climb.

This is the planning item that separates flying a twin from simply having two engines.

It moves both problems in dangerous directions at once:

• Performance gets worse. Single-engine climb drops sharply and the single-engine service ceiling falls, often below the surrounding terrain. You may have no positive single-engine climb at all.
• V_MC gets lower in a normally aspirated twin, which sounds helpful but means V_MC and the stall speed converge - so the failure mode shifts from a controllability problem toward a stall/spin problem.

The result is a takeoff where an engine failure after liftoff may simply not be survivable as a climb-out, and where the correct plan is to treat the twin like a single: land more or less straight ahead.

The mitigations are the ordinary ones - reduce weight, go early in the morning, use the longest runway, and brief a decision point honestly.

• The operating engine keeps burning from its own side, so over a long single-engine leg the airplane becomes laterally unbalanced, which adds to the rolling moment you are already holding.
• Crossfeed exists to let the operating engine draw from the tank on the failed side, both to use that fuel and to keep the airplane in lateral balance.
• Crossfeed is normally used in level cruise, not during takeoff or landing, and most AFMs prohibit it for takeoff and landing.
• Procedures are airplane-specific and getting them wrong can starve the running engine, so this is a checklist item, not a memory item.

Plan for it: on a long diversion, you want the fuel you can actually reach, and the tank on the dead side is not automatically available.

Abort. Close both throttles, maintain directional control, brake as required, and stop on the runway.

• Below V_MC you have no assurance of directional control airborne, so continuing is not a real option.
• Directional control on the ground with asymmetric thrust is itself a handful - closing both throttles removes the asymmetry immediately.
• Use maximum braking as needed, and be prepared to steer with rudder and differential braking.

This is the easy case, and it is only easy if you briefed it. The decision has to already be made before the takeoff roll starts.

If there is usable runway ahead, land on it. Reduce power on the operating engine to reduce the yawing moment, lower the nose, and put the airplane back down.

• Below V_YSE with the gear down and a windmilling propeller, a light twin usually cannot climb. Attempting to continue trades a landing you can make for a crash you cannot avoid.
• Retracting the gear to climb commits you before you know whether the airplane will climb at all.
• If you are airborne with no runway remaining and cannot climb, the decision becomes a controlled off-airport landing. Close the throttles first - with the asymmetry gone you can fly the airplane wings level - then land roughly straight ahead in the best area available. Slowing toward minimum speed while still carrying power on one side is how a forced landing turns into a V_MC rollover.

This is precisely why the takeoff briefing exists. The decision is made on the ground, not in three seconds at 50 feet.

• Gear down is a large drag penalty at the moment you have the least surplus power, and it is usually enough by itself to remove any single-engine climb.
• Gear down also signals that you are still in the phase where landing is a realistic option - the airplane is configured for it and you are close to the runway.
• Once the gear is up and you're climbing at V_YSE, you have committed to flying the airplane somewhere, and the problem becomes managing the pattern rather than stopping.

A widely used rule of thumb: if the gear is still down and there is runway ahead, land. It's a reasonable rule precisely because it removes the hesitation that kills people.

• Pitch for V_YSE immediately - the airplane will decelerate quickly with the yaw and drag.
• Rudder to stop the yaw, bank into the operating engine for zero sideslip.
• Clean up: mixtures, props, throttles forward; flaps up; gear up; cowl flaps as needed.
• Identify, verify, feather the failed engine.
• Secure the engine per the checklist.
• Assess: what climb do you actually have? Level off if that's all the airplane will do.
• Tell ATC, declare an emergency if appropriate, and get vectors to the nearest suitable airport.

The judgment item is honestly evaluating performance. If the airplane is only holding altitude, an approach you have to go around from is not available to you.

Better in every way that matters, which is why it's the phase used for training.

• You have altitude and airspeed, so there is time to work methodically rather than reflexively.
• You are already clean, so the drag reduction step is mostly just feathering.
• You can trade altitude for time while you run the checklist.

The process is the same - control, configure, identify, verify, feather, secure - but done deliberately and backed up with the printed checklist.

The new problem is where to go. Above the single-engine absolute ceiling the airplane slowly loses altitude until it settles there; below it, level flight is available but climb is little or none. Plan on the service ceiling either way, because the AFH warns that wear, turbulence, and pilot technique mean you may not hold altitude even at the published single-engine ceiling. Pick an airport you can reach from a descending profile, consider terrain, and start the diversion early rather than troubleshooting for ten minutes first.

• Let performance drive configuration. If the airplane is performing, the AFH's normal schedule still applies - gear down on downwind, confirmed abeam the intended landing point. If speed decays or the sink rate builds, hold off the remaining flaps until closer in. A partial-flap landing is fine.
• Fly V_YSE until you are certain of the landing, then slow only as required.
• Fly a normal 3° glidepath. Slightly steeper is acceptable; the long, flat, low final is the one the AFH tells you to avoid, because it leaves you leaning on power you don't have.
• Assume you cannot go around. With one engine inoperative and the airplane configured for landing, a go-around may be impossible. Make the first approach the one you land from.
• Brief and fly a stabilized profile, and don't accept a slam-dunk or a short-approach request from ATC.

The mental shift is that the landing becomes committed much earlier than usual.

It combines every adverse factor at once:

• Low airspeed, near or below V_YSE and closer to V_MC
• Full configuration - gear down, flaps out, maximum drag
• Low altitude, with no room to trade for speed
• A sudden power application on one side, producing a large yawing moment exactly when control authority is at its weakest
• Nose-up trim from the approach, encouraging a pitch-up toward the stall

That's a textbook V_MC rollover or a stall/spin entry, and the altitude available makes recovery unlikely.

The mitigation is procedural: with an engine out, treat the approach as committed to land. Configure late, stay at V_YSE until landing is assured, and don't put yourself in a position where a go-around is the only remaining option.

It is essentially a normal approach and landing - same pattern, same altitudes, same key positions. What changes is that there is less power and it's asymmetric, so the operating engine carries a higher-than-normal setting.

• V_YSE is the minimum airspeed all the way around. Hold it until the landing is assured, then slow to 1.3 V_S0 or the AFM speed. Don't add speed of your own; it only lengthens the roll.
• Gear down on downwind if performance allows, confirmed no later than abeam the intended landing point. Flaps typically 10° downwind, 25° on base.
• Let performance delay the flaps, not a rule. If speed decays or the sink rate builds, wait until closer in. A partial-flap landing is fine.
• Fly a normal 3° glidepath. Slightly steeper is acceptable; the long, flat, low approach is the one to avoid.
• Keep zero sideslip until you transition to land, and make power changes smoothly - a large, sudden application at low speed is a V_MC problem.
• Treat it as committed. A single-engine go-around is a risk to manage, not a plan.
• Pattern direction doesn't matter: the AFH calls turns toward the failed engine of no consequence for controllability and performance.

Late in the flare, as power comes off, the asymmetric yaw goes away, so be ready to release the rudder pressure you have been holding or the airplane will yaw the other way.

Dead foot, dead engine.

• The airplane yaws toward the failed engine, so you push the rudder on the operating side to stop it. The foot that is doing nothing is on the side of the dead engine.
• This works because it keys off a control input you are already making, not off an instrument you have to find and interpret.

Why not just read the gauges? On a sudden failure, engine instruments can be ambiguous or slow - a partial power loss may show near-normal indications, and manifold pressure can read high on a failed engine. The rudder never lies about which way the airplane is yawing.

Confirm with instruments once the airplane is under control, but identify with your feet first.

Because feathering the operating engine is unrecoverable at low altitude, and misidentification under stress is common.

To verify: slowly retard the throttle of the engine you believe has failed.

• If nothing changes - no change in yaw, sound, or performance - your identification was correct.
• If the airplane's behavior worsens, you had the wrong engine. Restore that throttle immediately.

Do it slowly and deliberately. The whole point is a reversible test before an irreversible action.

The step is skipped only where the AFM says so, and never as a time-saver.

Yes, in a few cases:

• Below the AFM's minimum altitude or airspeed for the procedure, where the manufacturer specifies flying the airplane first.
• When you are about to land anyway - Very low, with the runway made, securing the engine is less important than flying the landing.
• During training, where instructors commonly simulate a failure with zero thrust rather than actually feathering, to keep a restart from being necessary.
• When you have not verified which engine failed. Feathering the wrong one is worse than the drag of a windmilling propeller.

Also relevant: the ACS requires that Tasks involving actual feathering or shutdown be done only at a position and altitude where a safe landing on an established airport is possible if the propeller won't unfeather or the engine won't restart.

It depends on altitude, workload, and whether you have any idea what happened.

• Secure it if you are low, busy, close to an airport, or the cause is obvious and serious - fire, severe vibration, oil loss, mechanical noise. Never restart an engine that may be damaged or burning.
• Consider a restart only with plenty of altitude, the airplane stabilized and cleaned up, and a plausible cause you can address: fuel selector on an empty tank, a switched-off boost pump, carburetor ice, a magneto problem.

Order of operations matters. Fly the airplane, clean up the drag, get to a stable single-engine condition and on the way to an airport first. Troubleshoot only with whatever attention is genuinely left over, and always with the checklist.

• Accelerate-stop distance - The runway required to accelerate to a given speed, lose an engine, recognize it, and bring the airplane to a full stop.
• Accelerate-go distance - The runway (and air distance) required to accelerate to that speed, lose an engine, and continue the takeoff to a specified height, usually 50 ft.

Both are ACS knowledge items, but normal-category light twins don't all publish them - check your AFM, and where the data isn't there, brief from the takeoff and single-engine performance data you do have.

The critical point: unlike a transport-category airplane, a light twin has no requirement that these distances fit the runway, and no guarantee accelerate-go is even achievable. It's routine for accelerate-go to exceed the runway available, or for the chart to simply not extend to today's conditions - which is itself the answer.

How runway length enters the go/no-go decision: compare accelerate-stop against the runway available and accelerate-go against runway plus clearway. Check normal takeoff distance too - it's the easy number most people compute and then stop thinking. Runway in a twin buys you the ability to stop, which is usually your best option when an engine quits early, so a longer runway widens the window in which aborting is viable - exactly the window where a light twin's continue option is weakest.

Compute both before takeoff where the AFM publishes them. They are what turn a vague plan into a briefed decision point.

The point is to make every decision before you need it. A workable structure:

• Runway and performance - Runway length available, accelerate-stop distance if your AFM publishes it, and whether single-engine climb is positive at today's weight, altitude, and temperature.
• Speeds - Rotation speed, V_MC (red line), V_YSE (blue line), V_XSE if obstacles matter.
• The decision point - The specific condition that separates abort from continue. For example: any failure on the runway, abort; after liftoff with runway remaining and gear down, land; after liftoff, clean, and climbing at blue line, continue.
• The plan if you continue - Initial heading, altitude, obstacles or terrain, which airport you'll return to.
• The plan if you can't climb - Where you'll put it.

Say it out loud. The purpose is to convert a three-second reaction into the execution of a decision you already made.

To let you recognize the onset of loss of directional control with an engine inoperative, and to practice recovering from it promptly.

• It is a demonstration of a flight characteristic, not a maneuver you would ever perform operationally.
• It teaches the cues - the rudder running out of travel, the airplane starting to yaw despite full rudder, the buffet or stall warning.
• It also shows, concretely, that V_MC is not a fixed number: the speed at which you lose control in the demo will usually be well below red line, and at altitude the stall may arrive first.

It's Task X.B in both the Private and Commercial ACS.

Set up to approximate the certification conditions, which is what makes the demonstration meaningful:

• Landing gear up
• Flaps in the takeoff position
• Cowl flaps as required
• Trimmed for takeoff
• Both engines set to a safe starting power, then the critical engine reduced to idle (or simulated) and maximum power on the operating engine
• Propeller of the simulated failed engine windmilling (not feathered)
• Bank up to 5° toward the operating engine

Do it at an altitude that allows recovery no lower than 3,000 ft AGL, and clear the area thoroughly first.

• Enter high enough to complete the recovery no lower than 3,000 ft AGL.
• The reason is the realistic failure mode. If the demonstration goes wrong, it goes wrong as a stall with asymmetric thrust, which can rapidly develop into a spin - and a light twin has no approved spin recovery and can lose a great deal of altitude.

There's a second, subtler reason worth understanding: because V_MC decreases with density altitude while stall speed doesn't, a demonstration at altitude is inherently more likely to produce a stall than a genuine loss of directional control. The altitude that makes the maneuver safe is the same thing that makes it show you the stall case rather than the V_MC case.

• Clear the area and set up so the whole maneuver happens at least 3,000 ft AGL.
• Configure per the manufacturer; absent that, the ACS spells it out: gear up, flaps takeoff, cowl flaps takeoff, trim takeoff, props high rpm.
• Critical engine to idle with its propeller windmilling - not the zero-thrust setting used for the engine-failure Tasks - and the operating engine to takeoff power.
• Establish a climb attitude about 10 kt above V_SSE and a bank of up to 5° toward the operating engine.
• Increase pitch slowly to decelerate at about 1 knot per second, adding rudder as needed to hold heading.
• Continue to the first indication of loss of directional control, stall warning, or buffet.
• Recover immediately: reduce power on the operating engine enough to stop the yaw, lower the angle of attack, add no power on the failed engine, and recover within 20° of entry heading.

The deceleration rate is part of the standard. Going faster takes a steeper pitch attitude, which drives the angle of attack up and can carry you past the first cue before you recognize it - and a V_MC demo that degrades into a stall with high asymmetric thrust "may result in an unrecoverable loss of control and a fatal accident."

The first indication of any of three things:

• Loss of directional control - Full rudder is in and the airplane still begins to yaw
• Stall warning - Horn or light
• Aerodynamic buffet

Whichever comes first is your cue. You are not trying to find the "real" V_MC, and you never continue past the first indication to see what happens.

At altitude in a normally aspirated twin, the stall warning or buffet very often arrives before the loss of directional control, because V_MC has fallen below the stall speed. Recognizing that is part of the lesson.

Simultaneously:

• Reduce power sufficiently on the operating engine - This removes the asymmetric thrust causing the yaw
• Decrease the angle of attack as necessary to regain airspeed and directional control
• Do not add power on the simulated failed engine

Then recover to V_SSE/V_YSE as appropriate and advance power smoothly.

ACS standards:

• Recover within 20° of the entry heading
• Maintain V_SSE/V_YSE during recovery within ±5 kt (commercial) or +10/-5 kt (private)

The instinct to fix a yaw with more power on the good engine is exactly backwards here - it makes the yaw worse. Power comes off.

Because a stall with asymmetric thrust can rapidly develop into a spin, and light twins are not certified for spins or required to demonstrate spin recovery.

The ACS is explicit on the related hazard: do not perform this maneuver by increasing pitch attitude to a high angle with both engines operating and then reducing power on the critical engine. That technique is hazardous and may result in loss of airplane control - it sets up a yaw at high angle of attack, which is precisely how a spin starts.

The correct method establishes the asymmetric condition first, at a safe speed, then decelerates slowly toward it. And you stop at the first indication, every time.

Both. It is Task X.B in the Private ACS and Task X.B in the Commercial ACS, with the same knowledge elements, risk management elements, and procedure.

The only difference is the airspeed tolerance during recovery:

• Private - maintain V_SSE/V_YSE +10/-5 kt
• Commercial - maintain V_SSE/V_YSE ±5 kt

Both require recovery within 20° of the entry heading, and both require recovery at the first indication of loss of directional control, stall warning, or buffet.

This one catches people out, because the maneuver's reputation makes it sound like an advanced, commercial-only item.

They meter cooling air through the engine compartment. Open buys cooling and costs drag, so the schedule tracks where cooling demand is high and airspeed is low.

• Ground operations: fully open, unless the AFM/POH directs otherwise.
• Takeoff and climb: open. High power at low airspeed is the worst cooling case there is.
• Level off: closed, once cylinder head and oil temperatures are in their normal ranges. Lean the mixtures after the temperatures stabilize.
• Engine out, failed engine: closed. Of everything on the securing checklist, this is the only item that costs climb performance if you leave it undone.
• Engine out, operating engine: whatever the temperatures require. It is at high power and low airspeed with a long way to go, and cowl flaps are temperature control before they are a cleanup item.

That last pair is the same asymmetry as the rest of single-engine flight: clean up everything on the dead side, and keep the live engine alive even when it costs you drag.

• A governor senses engine RPM through flyweights and meters engine oil pressure to a piston in the propeller hub to change blade pitch. You select the RPM; the governor holds it as airspeed and power change.
• On speed - pilot valve centered, oil trapped in the hub, blade angle steady. Underspeed - the valve ports oil into the hub for a finer blade angle, unloading the engine. Overspeed - the valve ports oil out of the hub for a coarser angle, loading the engine down.
• Power setting order: RPM before manifold pressure when increasing, manifold pressure before RPM when reducing. That avoids unapproved high-MP/low-RPM combinations - approved ones in the AFM power charts are fine.

Which way oil pushes the blades is usually reversed on a twin. Most light piston twins use a full-feathering, counterweighted, oil-pressure-to-decrease-pitch propeller: governor oil drives the blades toward low pitch, while counterweights plus a spring or air charge drive them toward high pitch and ultimately feather. That is the opposite of the oil-pressure-to-increase-pitch arrangement on almost all singles, and it is why losing governor oil pressure moves a twin's propeller toward feather.

The oil path out and back

1. The engine-driven oil pump pressurizes the engine galleries, which feed the governor on its engine pad.
2. The governor's own gear pump boosts that supply to the much higher pressure needed to move the blades against the counterweights, spring, and centrifugal twisting moment. A relief valve returns the excess to the pump inlet.
3. Boosted oil leaves the pilot valve through passages in the engine and propeller shaft to the hub piston, driving the blades toward low pitch.
4. To coarsen pitch, the governor ports that oil to drain. The counterweights push the piston back, forcing hub oil back down the shaft, through the governor, and into the accessory case, where it drains to the sump for the engine pump to pick up again.

Two consequences follow. It is a closed loop on engine oil - the propeller has no separate supply, so a failed dome or transfer seal is an engine oil leak. And pulling the prop control into the feather detent simply ports hub oil to drain - feathering needs oil to leave the propeller, not arrive, which is why what stops you feathering a spun-down engine is the anti-feathering lock pins rather than any loss of oil pressure.

On a typical light twin with counterweighted, feathering propellers, the propeller moves toward feather.

• Oil pressure is what holds the blades out of feather. Lose it, and the counterweights and spring take over.
• This is the opposite of most single-engine airplanes, where oil pressure drives the blades toward high pitch and a loss of pressure sends the propeller to low pitch (high RPM).

The design choice makes sense for a twin: a failed engine that automatically feathers is a far better outcome than one that windmills flat and produces maximum drag.

• Synchronization matches the RPM of both propellers, eliminating the slow "beat" you hear when they are slightly different.
• Synchrophasing goes further and controls the relative blade position between the two propellers, so blades don't pass the fuselage at the same instant. That cuts cabin noise and vibration beyond what matching RPM alone achieves.

Both are comfort systems, not safety systems.

The operational point: turn them off before an engine failure situation and for takeoff and landing, per the AFM. A synchronizer chasing a failing engine can drive the good engine's RPM in an unhelpful direction, and it masks the RPM split that would otherwise be a useful cue.

Feathering turns the propeller blades edge-on to the relative wind (roughly 80-90° blade angle) so the propeller stops windmilling and produces minimal drag.

• On a typical light twin, oil pressure holds the blades out of feather. Counterweights and an internal spring drive them toward feather.
• Pulling the propeller control fully aft dumps governor oil pressure, and the counterweights and spring feather the blade.
• That design is deliberate: if the engine fails and oil pressure is lost, the propeller moves toward feather rather than toward flat pitch.

It's the highest-value action after an engine failure because it fixes controllability and performance together - it lowers V_MC and removes the single largest drag source.

Most light twins have antifeathering latches (spring-loaded pins) that engage below roughly 800-1,000 RPM.

• Their purpose is to keep the propeller from feathering every time you shut down on the ramp, which would make the next start difficult and put a large load on the starter.
• The consequence is that once a failed engine has spun down below that RPM, the latches engage and you can no longer feather it.

The practical rule: feather promptly. If you spend a long time troubleshooting while the propeller winds down, you may lose the option entirely and be stuck with a windmilling propeller for the rest of the flight. Exact RPM figures are airplane-specific - know your AFM's number.

• The normal method is to restart the engine. Move the propeller control forward, engage the starter, and as the engine turns, the governor restores oil pressure and drives the blades out of feather.
• Many training twins have an unfeathering accumulator - a small reservoir holding pressurized engine oil. Moving the propeller control forward releases that stored oil to the hub, kicking the blades out of feather so the engine windmills and starts without prolonged cranking.
• Expect noticeable vibration and a cold engine. Warm it before applying significant power.

This is why the ACS requires actual feathering or shutdown only where a safe landing at an established airport is possible if the propeller won't unfeather or the engine won't restart.

• A system that automatically feathers a propeller when it senses a large loss of power on that engine, typically via a torque or manifold-pressure sensor.
• Arming logic is AFM-specific. Many systems arm only for takeoff and landing; others cover initial climb and approach as well. The common thread is the phases where the delay of a manual identify-and-feather would be most costly - but never assume the system is live without checking your airplane's arming conditions and indication.
• It usually includes a lockout so that both propellers cannot feather at once, protecting against a false trigger on both sides.
• Common on turboprops, uncommon on piston trainers.

If your airplane has one, know how to arm it, how to tell it is armed, and what indication you get when it fires. If it doesn't, the point stands that you are the autofeather system, and your speed at identifying and feathering is the performance you actually have.

It lets an operating engine draw fuel from the tank on the opposite side.

• On most twins it's an emergency procedure: extend range and endurance in single-engine flight, and keep the airplane laterally balanced on a long OEI leg. A few models permit it as a normal fuel-balancing technique - your AFM says which kind you have.
• If a suitable airport is close by, there's no need to consider it at all.
• Never for takeoff, or for a normal landing with both engines running. The one exception: a single-engine landing on crossfeed, when returning the operating engine to its normal source would starve it.
• Otherwise terminate crossfeed before landing and return the operating engine to its main tank.
• Procedures are highly airplane-specific - which selector, which boost pump, in what order. Getting it wrong can starve the running engine.

Treat it as a checklist item, never a memory item. It also isn't urgent: get the airplane cleaned up, stabilized, and headed somewhere before reconfiguring fuel.

• Twins usually have more tanks - mains, auxiliaries, and sometimes tip tanks - each with its own rules about when it may be used.
• Many AFMs restrict auxiliary tanks to level cruise only, and require takeoff and landing on the mains.
• Some aux systems return unused fuel to a main tank, so running a main tank full and then selecting aux can vent fuel overboard.
• Unequal burn creates lateral imbalance, which matters more in a twin because you may already be holding a rolling moment.
• Each engine normally feeds from its own side, so "total fuel on board" overstates what a single operating engine can actually reach without crossfeed.

The habit worth building: know which tank feeds which engine, and track the burn on each side rather than in aggregate.

• Two engines means two alternators (or generators) feeding a common bus, usually through separate voltage regulators and with individual field switches and circuit breakers.
• Normal operation shares the load. Lose one alternator and the remaining one typically carries the entire load, though possibly with reduced margin.
• Many twins have a split bus or tie relay so that a fault on one side can be isolated.
• There may be two batteries, or one battery with a more complex bus structure.

For the oral, be ready to explain what indication you'd get for a single alternator failure, what load shedding you'd do, and whether your airplane can support the full electrical load - including known-ice and avionics - on one alternator.

Every retractable has an emergency extension method, and the type varies:

• Hydraulic systems typically have a hand pump, or a valve that dumps pressure and lets the gear free-fall into place, sometimes assisted by airspeed and gravity.
• Electric systems typically have a hand crank. Some AFMs have you pull the gear motor circuit breaker first so the motor doesn't fight the crank; others don't, and on some airplanes that breaker also feeds the position indication. Follow your AFM's sequence exactly rather than a generic one.

For your airplane:

• Most emergency extensions are one-way - once you've used it, you cannot retract the gear in flight.
• Slowing down often helps the gear fall and lock.
• Confirm three green and check the mechanical indicator if fitted.

Know the specific procedure and the airspeed limits from the AFM, and know where the crank or handle physically is.

• Anti-ice systems prevent ice forming and go on before you enter icing - heated pitot tube, heated stall warning vane, heated or alcohol-sprayed windshield, a propeller alcohol slinger ring, carburetor heat, engine inlet heat.
• Deice systems remove ice after a measurable amount has built up - most commonly pneumatic boots on the wing and tail leading edges, and electrically heated propeller boots that cycle through the blades to shed it.
• Sometimes the label follows the operation, not the hardware: cycled electrothermal propeller boots shed accumulated ice (de-ice) while continuous heating prevents it (anti-ice), and carburetor heat both prevents carb ice and clears it once formed. Read the placard.
• Alternate air is not ice protection. It's an alternate induction path for a blocked inlet or filter, and on many injected engines it opens automatically.
• Almost every airplane has some of this equipment, and a piece or two does not make an airplane approved for icing. Note also that § 91.205(d) does not itself require pitot heat for IFR - that comes from the AFM and the conditions you're operating in.

Known ice / FIKI approval

• FIKI means the airplane was certified with a complete, tested ice protection package and the AFM authorizes flight into known icing. It is an airplane-level certification, not a collection of parts - plenty of airplanes carry boots or a heated windshield without it.
• In a non-FIKI airplane, icing is an emergency in the making and the only plan is to leave: change altitude, reverse course, or land.
• Even with FIKI, the approval is a tool for leaving icing safely, not a license to loiter. No airplane is approved for severe icing, and ice raises stall speed while killing climb performance - your margins shrink exactly when you need them.

• A turbocharger uses exhaust gas to spin a turbine driving a compressor, which raises induction air pressure so the engine can make sea-level manifold pressure well above sea level.
• A wastegate controls how much exhaust bypasses the turbine. An automatic one holds target manifold pressure for you; a fixed or manual one puts overboost protection on the pilot.
• Critical altitude is the highest altitude at which the system can still maintain rated manifold pressure. Above it the wastegate is fully closed and power falls off like a normally aspirated engine.
• Turbonormalized systems only restore roughly sea-level manifold pressure (~29-30 inHg). A true turbocharged installation may be ground boosted above sea-level values, which makes overboost limits and cylinder pressures a bigger deal.

Operating concerns

• Overboost - move the throttle smoothly, especially with a fixed or manual wastegate.
• Heat - turbine inlet and exhaust temperatures run high. Watch TIT/EGT and CHT, and observe any cooldown at idle before shutdown so hot oil isn't left sitting in the bearings with no flow.
• Shock cooling - plan descents early rather than chopping power.
• Oil - the turbo is lubricated by engine oil, so an oil problem is now a turbocharger problem too.
• The airplane still has limits - a turbo extends engine performance, not the airframe's ceiling or the wing. Induction icing, § 91.211 oxygen requirements, and your own hypoxia tolerance all arrive before the engine runs out of manifold pressure.

In a single, the payoff is climb rate at altitude, higher cruise TAS, and topping weather or terrain - and the trap is being at oxygen altitudes in an unpressurized airplane.

In a twin, you get a much better single-engine ceiling and climb, but V_MC stays high: a normally aspirated twin's V_MC falls with altitude as the operating engine loses power, while a turbocharged twin holds full asymmetric thrust to critical altitude, so V_MC can remain above stall speed much higher up.

Specific numbers, wastegate type, and cooldown procedure are all AFM-dependent.

• A compressor feeds air into the cabin faster than it leaks out, and an outflow valve meters the escape. That balance sets cabin altitude - the pressure altitude the occupants actually feel.
• The source depends on the powerplant: bleed air from a turbine or turboprop, bleed air from a turbocharger on a piston airplane, or an engine-driven supercharger.
• Differential pressure is the cabin-to-ambient difference, limited by the structure. Max differential is what sets the lowest cabin altitude you can hold at a given flight level. Cabin rate of climb is how fast that cabin altitude is moving, controlled for comfort.
• Safety devices: a pressure relief valve (caps maximum differential), a negative pressure relief valve (keeps ambient from exceeding cabin pressure), and a dump valve to depressurize deliberately.

Losing the pressurization source. The cabin climbs toward ambient - gradually if it's a loss of source air, explosively if it's structural. The shape of the response is oxygen on, then descend, though the AFM procedure governs and a smoke or fire event can reorder the priorities. § 91.211 comes back into play the moment the cabin can no longer be held low. A rapid decompression adds fogging, noise, debris, cold, and a much shorter time of useful consciousness than the cabin altitude alone suggests.

In a twin, losing an engine may cost half your bleed air, so the system may not hold the differential even though the airplane flies fine - another reason a high-altitude engine failure means descending. In a pressurized single there is no second source at all, which is why those airplanes carry oxygen and treat the emergency descent as a memory item.

• Both engines, obviously - but specifically oil levels on each, and the cowl flaps on each.
• Propellers - Blade condition, and check for oil or grease at the hub, which can indicate a seal leak that would eventually prevent feathering.
• Fuel - More tanks, more sumps, more drains. Sump every one, and confirm the quantity in each rather than a total.
• Nacelles and gear - Hydraulic leaks, brake lines, gear doors and linkages, squat switch.
• Crossfeed and fuel selector - Check for freedom of movement and correct detents.
• Deice and anti-ice - Boot condition, prop boots, alcohol quantity, heated stall warning and pitot.
• Nose baggage - Loaded and secured within limits, because it affects CG meaningfully.

The mindset difference: you are inspecting two of most things, and a discrepancy on the side you overlook is the one that quits.

• Multiengine airplanes usually have more loading stations - nose baggage, aft baggage, multiple rows, and several fuel tanks - so there are more ways to get it wrong.
• The nose baggage compartment is a feature singles usually lack, and it's the main tool for pulling the CG forward.
• Fuel burn moves the CG measurably, so you check both takeoff and landing CG, not just takeoff.
• Useful load is often less generous than the airplane's size suggests. Full fuel and full seats is frequently not possible.
• Zero fuel weight may be a published limit, which singles rarely have.
• CG position changes V_MC, not just stability and elevator authority. An aft CG shortens the rudder arm and raises V_MC, so how you load the airplane sets your controllability margin with an engine out.

Because in a twin the CG position directly affects your control authority in an engine-out situation, not just handling qualities.

• The rudder's yawing moment is force times the arm from the CG to the rudder. An aft CG shortens that arm, so the same deflection produces less corrective moment, and V_MC rises.
• Certification determines V_MC at the most unfavorable (aft) CG, so a normally loaded airplane usually has margin - but a heavy aft load erodes it.
• An aft CG also reduces longitudinal stability and raises the risk of a stall at the worst moment.

Practical consequence: on a flight where single-engine performance is already marginal, loading forward buys you both a lower V_MC and better stall behavior.

• Enter with pressure altitude, temperature, weight, wind, and often runway slope and surface condition, and read out the distance to accelerate to the specified speed, lose an engine, react, and stop.
• Compare that to the runway available. If accelerate-stop exceeds it, an engine failure near that speed means going off the end.

What to do about it:

• Reduce weight, wait for cooler temperatures, or use a longer runway.
• Adjust the briefed decision point - if accelerate-stop doesn't fit, the honest brief is that above a certain speed you are going flying regardless.

Remember that chart figures assume a prompt reaction, a dry runway, and a new airplane. Add margin. And note the chart may not extend to today's conditions, which is itself a result worth respecting.

• Enter with weight, pressure altitude, and temperature to get single-engine rate of climb, assuming the critical engine feathered, gear and flaps up, zero sideslip, and V_YSE.
• A negative or zero result is a legitimate answer, not a chart-reading error. A light twin at gross on a hot day at a high field frequently cannot climb on one engine.

If it's negative, your options are to reduce weight, wait for cooler air, or accept that an engine failure after liftoff means a controlled off-airport landing - and brief it that way.

The discipline is to actually look. Part 91 doesn't require positive single-engine climb to take off, so the only thing standing between you and an unpleasant surprise is having run the numbers.

Follow the AFM, but the general shape is:

• Shut down and secure the burning engine - Mixture idle cutoff, fuel selector off, fuel pump off, and feather the propeller. Removing the fuel supply is the priority.
• Turn off that side's electrical items as directed - alternator field, and other nonessential loads.
• Do not attempt a restart on an engine that has been on fire.
• Fly the airplane on one engine using the normal OEI flow.
• Land as soon as possible - Not "as soon as practical." An extinguished fire can reignite, and structure may be compromised.
• Declare an emergency and tell ATC what you need.

Some AFMs suggest increasing airspeed to help extinguish the fire; know whether yours does rather than improvising.

• Situations: depressurization, smoke, or an engine fire.
• Airspeed and configuration come from the POH/AFM, not from a generic technique. Some call for idle power, gear down, flaps or speedbrakes; others don't use the gear at all, and extending it can be wrong for the airplane or the emergency. Fly the checklist.
• The bank angle is what the ACS fixes: 30-45°, to hold a positive load factor and keep the nose from rising as speed builds.
• Standards: clear the area first, airspeed +0/-10 kt, level off ±100 ft.
• Don't exceed V_LE with the gear down or V_LO in transit. In rough air use the AFM's turbulent-air penetration speed - and remember V_A decreases with weight.
• Level off at a safe altitude - minimum safe altitude for terrain, or a cabin-safe level after a depressurization.

The bank is the part people forget, and it's the one element that's the same in every airplane.

• Asymmetric flaps produce a strong rolling moment toward the retracted side. The response is to stop moving the flaps immediately - leave them where they are - and use aileron and rudder to hold the wings level.
  • Do not try to fix it by cycling the flaps.
  • Expect a higher approach speed and a longer landing, and plan a long, stable final. Consider that roll authority may run out at low airspeed, which sets a hard floor on approach speed.
• Asymmetric gear is primarily a landing problem - the airplane will want to swerve toward the extended side at touchdown. Try the emergency extension procedure, and if one main won't lock, plan the landing accordingly.

Both cases share a theme: stop making it worse, fly the airplane, and land somewhere long and into the wind.

Better off than a single, but not a non-event.

• Identify it - a low-voltage light, a zero or negative reading on that side's ammeter, or a split between the two.
• Attempt a reset of the alternator field per the checklist; a tripped field breaker sometimes resets.
• If it won't come back, the remaining alternator normally carries the whole load, but check the load against its rating. Known-ice equipment, pitot heat, landing lights, and a full avionics stack can exceed what one alternator will supply.
• Shed nonessential load proactively rather than waiting to discover the battery is discharging.
• Consider whether to continue. In IMC or at night, a single remaining alternator is a single point of failure, and landing at a suitable airport is usually the right call.

Losing both is a battery-endurance problem: shed everything but essentials, and land soon.