Multi-Engine Guide
Chair flying / Vmc Demonstration

Vmc Demonstration

Show the onset of a loss of directional control under asymmetric thrust and recover at the first indication — power back on the good engine and nose down, never more rudder.

Guided rehearsal is Premium

Pre-Takeoff Engine-Failure Briefing

  1. Runway, wind, and performance — takeoff distance, accelerate-stop, and single-engine climb for today's density altitude and weight
    Light twins are not required to have a positive single-engine rate of climb at any altitude. Know before you roll whether today's airplane will climb on one.
  2. Speeds: Vr, Vyse (blue line), Vmc (red line), Vsse
  3. Failure before rotation: throttles closed, brakes, stop straight ahead
  4. Failure after liftoff with runway remaining and gear down: close the throttles and land straight ahead
    The landing gear stays selected DOWN as long as there is usable runway or overrun to land on. Gear down means continued takeoff and climb is not recommended.
  5. Failure after liftoff with the gear up and no runway remaining: pitch Vyse, mixtures/props/throttles forward, flaps up, gear up, identify, verify, feather
  6. Climb straight ahead or with shallow turns to at least 400 ft AGL before turning back; obstacles and terrain off the departure end
  7. Who flies, who touches what, and the tolerance for any simulated failure — never below Vsse
    AFH: no engine failure should ever be introduced below Vsse; if none is published, use Vyse.

Setup

  1. Choose an altitude that allows the entire maneuver to be flown at or above 3,000 ft AGL“Altitude — three thousand AGL minimum”
    This is a demonstration of controllability, not performance — the airplane may lose several hundred feet. Altitude is the mitigation for the real hazard here, which is a spin entry under asymmetric power that twins are not required to demonstrate recovery from and generally recover from poorly.
  2. Clearing turns, then configure: gear up, flaps at the takeoff setting ({n:takeoffFlapSetting})
  3. Slow to approximately 10 kt above Vsse or Vyse, whichever is higher, and trim for takeoff
    The trim setting stays untouched for the rest of the maneuver — the rising control forces are part of what the demonstration is showing you.
  4. Pick an entry heading; propeller controls to high RPM on both engines

Execution

  1. Throttle the critical engine back to idle as the operating engine is advanced to the takeoff setting“Simulated failure — critical engine idle”
    In a twin without counter-rotating props the left engine is critical. If your airplane has a counter-rotating right engine, no engine is more critical than the other and the demonstration may be flown with either engine at idle — confirm the configuration in your AFM/POH. The gear warning horn will sound the whole time a throttle is retarded — do not let it mask the stall warning.
  2. Hold heading with rudder toward the operating engine; establish up to 5° of bank toward the operating engine“Heading held, five degrees of bank”
    Rudder does most of the work; the bank supplies a horizontal component of lift that helps it. Wings level makes Vmc significantly higher than published because that help is absent.
  3. Slowly raise the pitch attitude to decelerate at 1 kt per second — no faster“One knot per second”
  4. As control effectiveness decays, add rudder pressure and aileron to hold heading and bank
    Rudder force can be considerable — certification permitted up to 150 lb of force, though most twins run out of rudder travel long before that.
  5. First indication: an uncontrollable yaw toward the idle engine — OR any stall symptom“Loss of directional control”
    Stall symptoms count as the first indication just as much as the yaw does: stall warning horn or light, airframe or elevator buffet, or a sudden loss of control effectiveness. Whichever comes first ends the maneuver.

Recovery

  1. Simultaneously reduce power on the OPERATING engine and lower the nose to accelerate“Power back, nose down”
    Reducing the asymmetric thrust stops the yaw; lowering the pitch attitude regains flying speed and control authority. More rudder is not the recovery — you are already out of rudder, and holding it into a stall under asymmetric power is the classic fatal outcome. The airplane would depart toward the idle engine, not toward the applied rudder.
  2. Recover to straight flight on the entry heading at Vsse or Vyse
  3. Increase power on the operating engine and demonstrate controlled flight before restoring symmetrical power
  4. Level off, clean up, and note the altitude lost

ACS tolerances

  • Entry heading held to ±10° until the first indication
  • Deceleration no faster than 1 kt per second
  • Bank no more than 5° toward the operating engine
  • Entire maneuver at or above 3,000 ft AGL
  • Recovery initiated at the first indication — never allowed to reach a stall

Common errors

  • Recovering with more rudder instead of reducing power on the operating engine
  • Decelerating faster than 1 kt/sec, which reaches loss of control before the picture develops
  • Ignoring a stall warning because the yaw has not started yet — either one ends the maneuver
  • Entering from a high pitch attitude with both engines making power
  • Re-trimming during the maneuver and masking the rising control forces
  • Attempting the demonstration where density altitude puts Vmc at or below Vs — use the rudder-limiting technique instead