VMC Demonstration (AMEL, AMES)

This maneuver teaches recognition of and recovery from the loss of directional control that occurs below VMC — it is not a performance maneuver. State it to a student in one sentence, exactly like that.

The AFH frames OEI operations as two separate problems: pilots "learn to operate the airplane for maximum rate of climb performance at the blue radial indicated airspeed by training to fly without sideslip," and they "learn to recognize and recover from loss of directional control associated with the red radial indicated airspeed by performing a VMC demonstration. Since the object of a VMC demonstration is not performance, sideslip occurs during the maneuver" (AFH 13-23).

Follow it with the consequence: "Maintaining altitude is not a criterion in accomplishing this maneuver. This is a demonstration of controllability, not performance" (AFH 13-26).

Current (14 CFR part 23 section 23.2135(c)): the calibrated airspeed at which, following the sudden critical loss of thrust, it is possible to maintain control of the airplane.

Historical (section 23.149): the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control with that engine still inoperative and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5°. "This definition still applies to airplanes certified under that regulation" — which is most of the training fleet (AFH 13-1 to 13-2).

Neither promises climb: there is no requirement under either determination that the airplane be capable of climbing at this airspeed — VMC only addresses directional control (AFH 13-2).

Historical dynamic VMC was determined under 14 CFR part 23 section 23.149 with (AFH 13-24 to 13-25):

• Maximum available takeoff power initially on each engine — 23.149(b)(1)
• Propeller controls in the recommended takeoff position throughout, so the critical engine propeller is windmilling unless autofeather is installed — 23.149(b)(5)
• Most unfavorable weight and CG — 23.149(b)
• Landing gear retracted — 23.149(b)(4)
• Flaps in the takeoff position (wing and cowl; for most twins, 0°) — 23.149(b)(3)
• Trimmed for takeoff — 23.149(b)(2)
• Airborne, ground effect negligible — 23.149(b)
• Maximum of 5° angle of bank toward the operating engine — 23.149(a)

Teaching point: the demonstration setup in AI.XIII.B.S1 is a deliberate re-creation of that list.

VMC increases with (AFH 13-24 to 13-25):

• More power on the operating engine. Normally aspirated: VMC highest at takeoff power and sea level, decreasing with altitude. Turbocharged: takeoff power and therefore VMC stay constant up to the engine's critical altitude, then decrease.
• More drag on the inoperative engine — highest with the propeller windmilling at low pitch, high rpm.
• Aft CG — the rudder's moment arm and therefore its effectivity are reduced.
• Reduced weight — "VMC increases as weight is reduced."
• Landing gear retracted — extended gear aids directional stability, decreasing VMC.
• Less bank toward the operating engine — the big one.

Teach it as a memory list, then make the student explain the why behind each. Rote is not understanding.

More than any other factor. "VMC may increase more than 3 knots for each degree of bank reduction between 5° and wings-level," so with the wings held level "loss of directional control may be experienced at speeds almost 20 knots above published VMC" (AFH 13-25).

The mechanism: "The horizontal component of lift generated by the bank balances the side force from the rudder, rather than using sideslip to do so. Sideslip requires more rudder deflection, which in turn increases VMC" (AFH 13-25).

And the caution your student must hear: the 5° limit is "a historical limit imposed upon manufacturers," and it "does not inherently establish zero sideslip or best single-engine climb performance." Zero sideslip may occur at bank angles less than 5° (AFH 13-25).

• VMC (red line) — minimum control speed. Directional control only, no climb promise (AFH 13-2).
• VSSE — safe, intentional one-engine-inoperative speed: "the minimum speed to intentionally render the critical engine inoperative" (AFH 13-1). This is your training floor, not a performance speed.
• VYSE (blue line) — best rate of climb with OEI; above the single-engine absolute ceiling it yields minimum rate of sink (AFH 13-1).
• VS — stall speed, which is an AOA limit, not a control limit.

The relationship that matters: with normally aspirated engines VMC decreases with altitude while VS stays the same. "At sea level there is usually a margin of several knots between VMC and VS, but the margin decreases with altitude, and at some altitude, VMC and VS are the same" (AFH 13-26).

Run the force balance for them. The operating engine's thrust acts out on the wing, producing a yawing moment about the CG. The rudder produces an opposing side force, and that force is proportional to dynamic pressure — it falls off with the square of airspeed.

Asymmetric thrust does not decrease as you slow down; in fact it grows, because the pitch attitude is rising and P-factor loads the descending blade of the operating engine harder (AFH 13-23). So one moment is constant or growing while the other is shrinking.

"An airspeed is soon reached where full right rudder travel and up to a 5° right bank can no longer counteract the asymmetrical thrust, and the airplane will begin to yaw uncontrollably toward the dead engine" (AFH 13-26).

The critical engine is "the engine whose failure had the most adverse effect on directional control" (AFH 13-23).

On twins with both engines rotating conventionally (clockwise from the pilot's seat), the left engine is critical. Both engines are subject to P-factor: at positive AOA under power, the descending blade produces greater thrust. The descending blade of the right engine is farther from the CG, so it has the longer moment arm. Failure of the left engine therefore leaves the more powerful yawing moment (AFH 13-23).

With a counter-rotating right engine, "the degree of asymmetrical thrust is the same with either engine inoperative. No engine is more critical than the other, and a VMC demonstration may be performed with either engine windmilling" (AFH 13-23).

Per the manufacturer; absent that, at VSSE or VYSE as appropriate, with (AI.XIII.B.S1a–g):

• Landing gear retracted
• Flaps set for takeoff
• Cowl flaps set for takeoff
• Trim set for takeoff — and the trim setting remains unaltered for the rest of the maneuver (AFH 13-26)
• Propellers set for high rpm
• Power on the critical engine reduced to idle, propeller windmilling
• Power on the operating engine set to takeoff or maximum available

Then establish a single-engine climb attitude with airspeed approximately 10 knots above VSSE (AI.XIII.B.S2) and a bank of not more than 5° toward the operating engine (AI.XIII.B.S3).

Slow and deliberate, one knot per second (AI.XIII.B.S4, AFH 13-26):

1. "Entry heading is 090, and we finish above 3,000 AGL."
2. "High rpm both. Left throttle to idle, right throttle to takeoff power — smoothly."
3. "The gear horn will sound the whole time. Listen past it for the stall warning."
4. "Right rudder holding heading. Up to five degrees of right bank."
5. "I'm raising the nose slowly — one knot per second, no faster. Feel the rudder pressure build."
6. "Aileron is going in too, just to hold the bank."
7. "Watch the ball, watch the heading, and listen."

The rudder force can be substantial: certification permitted 150 pounds of force under 23.149(e), and "most twins will run out of rudder travel long before 150 pounds of pressure is required" (AFH 13-26).

Recover at the first indication of loss of directional control, stall warning, or buffet (AI.XIII.B.S5) — by simultaneously:

• Reducing power sufficiently on the operating engine to stop the yaw, and
• Decreasing the angle of attack as necessary to regain airspeed and directional control,
• without adding power on the simulated failed engine (AI.XIII.B.S6).

The universal student error is more rudder. There is no more rudder — running out of it is the definition of the event. The AFH is explicit: "the pilot simultaneously retards the throttle for the operating engine to stop the yaw and lowers the pitch attitude to regain speed" (AFH 13-26). Teach the hand and the yoke as one motion, and rehearse it on the ground before you ever fly it.

Recover within 20° of entry heading (AI.XIII.B.S7), then advance power smoothly on the operating engine and accelerate to VSSE/VYSE, as appropriate, ±5 knots during recovery (AI.XIII.B.S8).

The 20° is not arbitrary — dynamic VMC in certification was "the minimum speed at which directional control could be maintained within 20° of the original entry heading when a cut of the critical engine was made" (AFH 13-25).

Then: "Recovery is made to straight flight on the entry heading at VSSE or VYSE. The pilot increases power to the operating engine, and demonstrates controlled flight before restoring symmetrical power" (AFH 13-26). Do not shove both throttles up while the airplane is still yawing.

That the demonstration degrades into a single-engine stall. "A VMC demonstration that is allowed to degrade into a single-engine stall with high asymmetrical thrust may result in an unrecoverable loss of control and a fatal accident" (AFH 13-26).

Why it's unrecoverable: at the stall under asymmetric power, "a spin entry is likely. The yawing moment induced from asymmetrical thrust is little different from that induced by full rudder in an intentional spin" — and the airplane departs in the direction of the idle engine, not the direction of applied rudder. No multiengine airplane is approved for spins, and their spin recovery characteristics "are generally very poor" (AFH 13-26, 13-18).

Terminate the maneuver on any stall symptom: warning light or horn, airframe or elevator buffet, or sudden loss of control effectiveness (AFH 13-26).

• Decelerating too fast. Anything quicker than 1 knot per second blows past the first indication (AI.XIII.B.S4). Correction: "pitch for one knot per second and let the airplane come to you."
• Wings level or too much bank. Level wings raise VMC substantially (AFH 13-25); more than 5° understates it and adds sideslip.
• Recovering with rudder. Cover it in the brief and again in the debrief.
• Missing the first indication — usually because the gear warning horn masks the stall warning. "Noise within the flight deck may mask the sound of the stall warning horn" (AFH 13-26).
• Adding power on the failed engine during recovery (AI.XIII.B.S6).
• Retrimming during the maneuver — the trim stays where it was set for takeoff (AFH 13-26).
• Heading loss beyond 20° during recovery.

• Altitude. Select an entry that keeps the whole maneuver at or above 3,000 feet AGL — "remaining at or above a minimum of 3,000 feet AGL throughout the maneuver is considered to be effective risk mitigation of certain hazards" (AFH 13-26). The evaluator selects entry altitude on this basis too (ACS Appendix 2).
• Stall symptom — take it, reduce AOA as the throttle comes back, return to entry airspeed. Do not wait to see whether the student catches it. "The learner may be highly focused on the directional control aspect of the maneuver to the extent that impending stall indications go unnoticed" (AFH 13-18).
• Never enter from a high pitch attitude with both engines running and then reduce power on one (AFH 13-27).
• Clear the area and keep a scan going — collision avoidance is yours while the student is inside the flight deck.

Two determinations, and if they differ, the higher of the two is published (AFH 13-23).

Dynamic: test pilots made mixture cuts of the critical engine at progressively lower speeds; VMC is the minimum speed at which control could be maintained within 20° of the original entry heading (AFH 13-25). "This technique is only used by highly experienced test pilots during aircraft certification. It is unsafe to be attempted outside of these circumstances" (AFH 13-23).

Static: simply the ability to maintain straight flight at VMC with a bank angle of not more than 5°. "This more closely resembles the VMC demonstration task in the practical test" (AFH 13-23).

Say the corollary to your student explicitly: attempting to demonstrate VMC with an engine cut from high power, or intentionally failing an engine below VSSE, "creates a high likelihood for loss of control and an accident" (AFH 13-25).

Use the rudder-blocking technique. "An actual demonstration of VMC may not be possible under certain conditions of density altitude, or with airplanes whose VMC is equal to or less than VS. Under those circumstances, as a training technique, a demonstration of VMC may safely be conducted by artificially limiting rudder travel to simulate maximum available rudder. A speed well above VS (approximately 20 knots) is recommended when limiting rudder travel" (AFH 13-27).

"The rudder limiting technique avoids the hazards of spinning as a result of stalling with high asymmetrical power, yet is effective in demonstrating the loss of directional control" (AFH 13-27). The AFH names it specifically as an instructor tool for VMC demonstrations (AFH 13-18).

Brief the block before you fly it — the student must know the pedal will stop early and that stopping is the point.

This is the explanation phase, done on the ground, before the airplane moves (AIH 9-5):

• Objective — recognize and recover from loss of directional control; this is a controllability demonstration, not a performance maneuver.
• Elements — clearing, configuration checklist, entry, deceleration rate, the three first-indications, the recovery.
• Completion standards — recover at the first indication, within 20° of entry heading, accelerate to VSSE/VYSE ±5 knots.
• What it will feel like — very heavy rudder, increasing aileron to hold the bank, a nose-high attitude, the gear horn blaring the whole time.
• Safety — the 3,000-foot floor, who is watching for traffic, the three-step exchange of controls, and the sentence you will say if you take it.

The AFH's own multiengine training rules start here: brief "the objectives, maneuvers, expected learner actions, and completion standards before the flight begins," and establish "a clear understanding... as to how simulated emergencies will be introduced" (AFH 13-35).

Two misconceptions get planted here, and the law of primacy says whatever they learn first is nearly unshakable. The first: "red line is a speed I can fly." It is not — VMC is where control ends, not a target; every real engine-out speed you teach is blue line or above. The second: "if I run out of rudder, I need more rudder." The correction is power off the good engine and nose down.

The countermeasure is a debrief that names both explicitly, plus contrast flying: run the VMC demonstration and then immediately fly the zero-sideslip climb from Task XIII.A at blue line. Same airplane, same day, one maneuver about control and one about performance — the two problems the AFH says define OEI flight (AFH 13-23).