Beech 95B55 N180GA accident near Plattsburgh, New York

Probable cause

The pilot's failure to maintain the proper airspeed and his exceedance of the airplane's critical angle-of-attack during a single-engine approach, which resulted in an aerodynamic stall at an altitude too low for the flight instructor to recover.

NTSB analysis

The flight instructor of the multi-engine airplane reported that during a full-feathered, single-engine practice instrument approach in visual meteorological conditions, the pilot extended the flaps and the airspeed dropped about 20-30 knots. He further reported that the pilot added power to the operating engine and the airplane "veered" to the left and "lost more altitude resulting in a stalled condition". The flight instructor took control of the airplane, reduced power to idle on the operating engine, attempted to level the wings, and the airplane impacted the airport ramp area with "excessive vertical speed".

The airplane sustained substantial damage to both wings, both ailerons, and fuselage.

The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation.

The Federal Aviation Administration has published the Airplane Flying Handbook FAA-H-8083-3B (2016). This handbook discusses multi-engine landings and spin awareness and states in part:

Landings

The final approach should be made with power and at a speed recommended by the manufacturer; if a recommended speed is not furnished, the speed should be no slower than the single-engine best rate-of-climb speed (VYSE) until short final with the landing assured, but in no case less than critical engine-out minimum control speed (VMC). Some multiengine pilots prefer to delay full flap extension to short final with the landing assured. This is an acceptable technique with appropriate experience and familiarity with the airplane.

Spin Awareness

In order to spin any airplane, it must first be stalled. At the stall, a yawing moment must be introduced. In a multiengine airplane, the yawing moment may be generated by rudder input or asymmetrical thrust. It follows, then, that spin awareness be at its greatest during VMC demonstrations, stall practice, slow flight, or any condition of high asymmetrical thrust, particularly at low speed/high AOA (angle of attack). Single-engine stalls are not part of any multiengine training curriculum.

For spin avoidance when practicing engine failures, the flight instructor should pay strict attention to the maintenance of proper airspeed and bank angle as the student executes the appropriate procedure. The instructor should also be particularly alert during stall and slow flight practice. Forward center-of-gravity positions result in favorable stall and spin avoidance characteristics, but do not eliminate the hazard.

Text from the NTSB. Open the NTSB docket for GAA17CA061 for the full record.