Vmc is an important speed in a twin engine aircraft. It is marked on the airspeed indicator by a red radial line. In the Seneca (III and IV), this speed is 66 knots. Vmc is the minimum speed at which directional control can be maintained under given conditions. See the Factors Affecting Vmc handout for details. In reality, this speed may be higher or lower than 66 knots. For this reason, immediately close both throttles if directional control cannot be maintained, no matter what the airspeed.

For the Vmc demonstration, begin by completing the pre-maneuver checks. The FAA requires the aircraft to maintain 3,000 feet AGL for multiengine maneuvers. Piper recommends at least 4,000 feet AGL for the Seneca. Set the throttles initially to 20” each to help slow the plane. Then fail one engine by closing the throttle. Bring the other engine up to takeoff power.

Smoothly pitch back to decrease the airspeed at a rate of approximately one knot per second. Keep 3-5 degrees of bank into the good engine. As the airspeed decreases, you will need to increase rudder pressure and aileron pressure to maintain directional and roll control.

Recover immediately when any of the following happen:
Loss of directional control (rudder at the stop)
Stall warning horn
Stall buffet
Reaching Vmc (66 kts)
Initiate the recovery by closing both throttles and pitching down to gain airspeed. Upon reaching Vsse (85 knots), increase the throttle of the operating engine to takeoff power, maintain directional control, and climb out at 92 knots. Match the throttles at cruise setting and resume normal cruise flight.

Caution: Do not stall the aircraft in a single engine condition! Since stall speed and Vmc are very close, it is likely that the aircraft will stall in an uncoordinated condition, possibly leading to a spin.