One Engine Inoperative (OEI) Performance (AMEL, AMES)

80 to 90 percent (AFH ch. 13). In some cases the ability to climb or even maintain altitude in a light twin simply does not exist after an engine failure.

The arithmetic behind it: climb rate comes from excess thrust horsepower, not total power. Losing half the power removes most of the surplus above what is needed for level flight, and the windmilling propeller, the sideslip, and the deflected control surfaces all add drag on top. This is the single most important number to teach a multiengine student, because it reframes the second engine from "a spare" into "an option that has to be earned."

• Single-engine service ceiling — the altitude at which the airplane can no longer maintain a 50 fpm rate of climb with one engine inoperative
• Single-engine absolute ceiling — where climb is no longer possible with OEI

For comparison, the all-engine service ceiling is where the airplane can no longer maintain 100 fpm with both engines operating (AFH ch. 13). Above the single-engine absolute ceiling, VYSE yields the minimum rate of sink — the drift-down speed (AFH ch. 13).

Under ideal conditions the accelerate-go distance only brings the airplane to a point 50 feet above the takeoff elevation — little more than one wingspan above level, unobstructed terrain. To get even that, the pilot had to instantly recognize and react, retract the gear, identify and feather the correct engine, all while holding precise airspeed and bank (AFH ch. 13).

AFH's illustration: at a 150 fpm climb at a 90-knot VYSE, it takes about 3 minutes to climb the additional 450 feet to 500 ft AGL, covering another 5 NM, at a climb gradient of about 1.6 percent. Any turn — such as back toward the airport — seriously degrades that already marginal performance.

• VMC — the calibrated airspeed at which, following the sudden critical loss of thrust, it is possible to maintain control of the airplane. Marked with a red radial line (AFH ch. 13, 14 CFR 23.2135(c)).
• VXSE — best angle of climb, OEI
• VYSE — best rate of climb, OEI. Marked with a blue radial line. Above the single-engine absolute ceiling it yields minimum sink.
• VSSE — safe, intentional one-engine-inoperative speed: the minimum speed at which to intentionally render the critical engine inoperative.

(AFH ch. 13.) The instructor discipline: no engine failure is ever introduced below VSSE; if no VSSE is published, use VYSE (AFH ch. 13).

VMC is a control speed; VS is an aerodynamic speed. Density altitude moves them in opposite directions relative to each other:

• With normally aspirated engines, VMC is highest at takeoff power at sea level and decreases with altitude, because the operating engine makes less power and therefore less asymmetric thrust (AFH ch. 13).
• Indicated stall speed does not change with altitude.

So at high density altitude, VMC can fall below VS — meaning the airplane will stall before it loses directional control, and the stall arrives with high asymmetric power and a large yaw. That is the recipe for a spin. AFH ch. 13 notes that with turbocharged engines, takeoff power and therefore VMC remain constant with altitude up to the engine's critical altitude, then decrease as with a normally aspirated engine.

VX and VXSE are often perilously close to VMC, leaving scant margin for error if an engine fails as VXSE is assumed. If flaps were used for takeoff, the situation is worse because of additional drag. AFH ch. 13 gives a hard planning rule: if VX is less than 5 knots higher than VMC, give strong consideration to reducing useful load or using another runway.

The critical engine is the engine whose failure has the most adverse effect on directional control. On twins where both engines rotate clockwise as viewed from the pilot's seat, that is the left engine (AFH ch. 13).

The reasoning is P-factor: at positive angles of attack the descending blade of each engine produces greater thrust than the ascending blade. The descending blade of the right engine is farther from the center of gravity and therefore has a longer moment arm. So losing the left engine leaves the right engine producing thrust through the longer arm — maximum asymmetric yaw (AFH ch. 13).

On a counter-rotating twin, asymmetric thrust is the same either way, neither engine is critical, and a VMC demonstration may be performed with either engine windmilling.

Historically under 14 CFR 23.149 (AFH ch. 13):

• Maximum available takeoff power initially on each engine — VMC increases as power increases
• Propeller controls in the recommended takeoff position — VMC is highest with the critical engine's propeller windmilling at low pitch, high rpm
• Most unfavorable weight and CG — VMC increases as CG moves aft (shorter rudder moment arm) and as weight is reduced
• Landing gear retracted — extended gear aids directional stability and lowers VMC
• Flaps in the takeoff position — for most twins, 0°
• Trimmed for takeoff
• Airborne, ground effect negligible
• Maximum 5° angle of bank

Historically, VMC is the sea level calibrated airspeed at which, with the critical engine suddenly made inoperative, control can be maintained and then straight flight held at the same speed with a bank of not more than 5°.

Enormously — VMC increases roughly 3 knots per degree of bank reduction between 5° and wings-level, so loss of directional control can be experienced at speeds almost 20 knots above published VMC with the wings held level (AFH ch. 13).

Mechanism: banking toward the operative engine produces a horizontal component of lift that balances the side force from the rudder. Without it, sideslip does that job, and sideslip requires more rudder deflection — which raises VMC.

No, and this is a favorite examiner question. The 5° maximum is a historical certification limit imposed on manufacturers; it does not inherently establish zero sideslip or best single-engine climb performance. Zero sideslip, and therefore best OEI climb, may occur at bank angles less than 5° (AFH ch. 13). Certification VMC is concerned only with the minimum speed for directional control under one specific set of conditions — not with the optimum attitude for climb.

The actual bank angle for zero sideslip varies among airplanes from about one and one-half to two and one-half degrees (AFH ch. 13).

Zero sideslip is the attitude that gives the airplane its smallest profile to the relative wind, minimizing drag. In a single, or a twin with both engines running, the centered ball indicates it — but with an engine inoperative, the centered ball no longer indicates zero sideslip, because asymmetric thrust means no flight deck instrument directly shows it (AFH ch. 13).

So the pilot flies a predetermined bank angle and ball position instead. AFM/POH single-engine performance charts were determined at zero sideslip, so this technique is what makes the charted numbers achievable.

Two forces can counter asymmetric thrust: yaw from the rudder, and the horizontal component of lift from bank. Used alone, neither is correct (AFH ch. 13):

1. Wings level, ball centered — requires large rudder toward the operative engine and produces a moderate sideslip toward the inoperative engine. Climb performance is reduced, and VMC is significantly higher than published because there is no horizontal lift component helping the rudder.
2. Ailerons alone — requires an 8–10° bank toward the operative engine with no rudder input, ball well displaced toward the operative engine, and climb performance greatly reduced by a large sideslip toward the operative engine.
3. Both, in the correct combination — zero sideslip, maximum climb performance (AFH ch. 13). Without specific manufacturer guidance, a bank of about 2° with one-third to one-half ball deflection toward the operative engine is suggested; VYSE is maintained with pitch (AFH ch. 13).

Best OEI climb performance requires VYSE, maximum available power, and minimum drag — flaps and gear retracted, failed propeller feathered, sideslip minimized.

The in-flight demonstration resembles static VMC determination in certification, not the dynamic version (AFH ch. 13). Setup and sequence:

1. Altitude that allows the maneuver at least 3,000 ft AGL, clearing turns complete.
2. Landing gear retracted, flaps in the takeoff position, slow to approximately 10 knots above VSSE or VYSE, whichever is higher, and trim for takeoff — the trim setting is not altered for the remainder of the maneuver.
3. Select an entry heading; high rpm on both propellers. Throttle the left (critical) engine to idle as the right engine is advanced to takeoff power.
4. Counteract the left yaw and roll primarily with right rudder; establish a bank of up to 5° toward the operating engine as appropriate for the make and model.
5. Holding the entry heading, slowly increase pitch to decelerate at 1 knot per second — no faster. Add rudder as control effectiveness decays; aileron displacement increases to hold the bank.
6. Recovery at the first of either loss of directional control or the first indication of a stall.

(AFH ch. 13.) The gear warning horn sounds throughout because a throttle is retarded — teach the student to listen through it for the stall warning horn and watch for the stall warning light.

Recovery is to straight flight on the entry heading at VSSE or VYSE, then power is increased on the operating engine (AFH ch. 13). Your non-negotiables as the instructor:

• Never introduce an engine failure below VSSE; if none is published, use VYSE (AFH ch. 13).
• Never demonstrate VMC from a high pitch attitude with both engines operating and then reduce power on one — that sequence markedly raises loss-of-control risk (AFH ch. 13).
• Recover at the first sign of an impending stall, not at loss of directional control, if the stall indication comes first.
• Slow flight is not the place for engine cuts: the airplane is well below VSSE and very close to VMC, with degraded stability and stall warning (AFH ch. 13).

AFH ch. 13 states that spin awareness should be at its greatest during VMC demonstrations, stall practice, slow flight, or any condition of high asymmetric power.

At some density altitudes, or in airplanes whose VMC is equal to or less than VS, a true demonstration is unsafe. As a training technique, VMC may be demonstrated by artificially limiting rudder travel to simulate maximum available rudder, using a speed well above VS — approximately 20 knots above is recommended (AFH ch. 13). The rudder-limiting technique avoids the hazard of stalling with high asymmetric power while still demonstrating the loss of directional control.

• Decelerating too fast. The standard is 1 knot per second (AFH ch. 13); faster hides the progressive control degradation that is the entire teaching point.
• Fixating on directional control. AFH ch. 13 warns specifically that the learner may be so focused on heading that impending stall indications go unnoticed. Assign the stall warning to yourself out loud during the first few.
• Retrimming during the maneuver. Trim stays at the takeoff setting.
• Letting bank creep past 5° to make the heading easier — which flatters VMC and teaches the wrong sight picture.
• Recovering with pitch alone and leaving the yaw uncorrected.

The decision must be made before the takeoff roll, not during it. AFH ch. 13 puts it as the last item of the before-takeoff checklist: review, in advance, what you will do if an engine fails at any point.

The speeds, in sequence:

• Below VMC on the ground — reject. Directional control is maintained only by promptly closing both throttles and using rudder and brakes (AFH ch. 13).
• Below VMC airborne — the airplane should never have been airborne below VMC. Use the manufacturer's VR or VLOF; if none is published, use VMC plus 5 knots for VR (AFH ch. 13).
• After liftoff — AFH ch. 13's general recommendation: if the landing gear has not been selected up, reject the takeoff, even if airborne. Raise the gear not later than VYSE, and once it is up, treat it as a GO commitment if climb performance exists.

Teach the student to say the decision out loud before every takeoff. A decision made at 200 feet with a yawing airplane is not a decision.

By making the student compute it, which is exactly what AI.II.P.S1 asks. Before every training flight, pull the AFM/POH single-engine climb chart and work the actual conditions: weight, pressure altitude, temperature. Compare the answer to the terrain and to the single-engine service ceiling.

AFH ch. 13's framing: if single-engine climb performance is adequate and the airplane has been promptly and correctly configured, the climb may be continued; if climb is unlikely or impossible, a landing has to be made in the most suitable area, even off-airport. Above all, avoid attempting to continue flight beyond the airplane's performance capability.

Note also that accelerate-stop distance is published in most AFM/POHs only as advisory data — it becomes a limitation only when it appears in the limitations section (AFH ch. 13). Experienced multiengine pilots insist on runway lengths of at least accelerate-stop distance as a matter of practice.

It converts an engine failure from a climb problem into a drift-down problem. Above the single-engine absolute ceiling the airplane slowly loses altitude; hold VYSE to minimize the rate of altitude loss, and expect the drift-down rate to be greatest immediately following the failure (AFH ch. 13).

Planning consequence: know your single-engine service ceiling for today's weight and temperature before you launch over a ridge, and pick a route with an escape valley rather than a route that assumes the second engine.

Because both directly move the numbers you just computed. Weight above gross and CG aft of limits both degrade single-engine climb and raise VMC — VMC increases as CG moves aft (AFH ch. 13). And in a twin, fuel mismanagement is the most common way to create a genuine engine failure at the least convenient moment: crossfeed configuration, tank selection during the climb, and unporting in a slip are all instructor-supervised items on early flights.

Teach the student to verify the performance assumptions rather than inherit them: charts are determined under ideal flight-testing conditions and it is unlikely that performance is duplicated in service conditions (AFH ch. 13).