Beech 35 N6129V accident near Hilltown Township, Pennsylvania

Probable cause

The pilots’ exceedance of the airplane’s critical angle of attack while practicing maneuvers during an instructional flight, which resulted in an aerodynamic stall and and a loss of airplane control.

NTSB analysis

The flight instructor and the pilot receiving instruction were conducting a flight in an airplane that the pilot receiving instruction owned, and the purpose of the accident flight was to prepare him for the commercial pilot practical examination. About 30 minutes after takeoff, the airplane was maneuvering at an altitude of about 1,600 ft above ground level. The airplane then entered a left spin and descended toward the ground, impacting a residential street.

A witness stated that he heard a singleengine airplane overhead and thought the airplane’s loud engine sound did not match its slow airspeed, which meant to him that the airplane was most likely in a steep climb to practice a stall. The witness looked up again and saw the airplane diving almost straight down and twisting toward the ground.

Examination of the wreckage revealed no preimpact mechanical malfunctions. Review of automatic dependent surveillance-broadcast (ADS-B) data revealed that the airplane’s maneuvers during the final portion of flight were conducted below its flaps-up, idle power stall speed and were twice briefly below the flaps-down stall speed. During the final 30 seconds of flight, the airplane rolled rapidly to the left when engine noise was reduced. The airplane’s rapid left roll and loss of altitude were consistent with an aerodynamic stall. Thus, the pilot who was flying (which could not be determined based on the available evidence) allowed the airplane’s critical angle of attack to be exceeded, resulting in a loss of airplane control.

Toxicological testing detected ethanol and metoprolol in the flight instructor’s specimens. The most likely source of the ethanol was postmortem production; therefore, the identified ethanol did not contribute to the circumstances of the accident. Although direct effects from the flight instructor’s use of metoprolol likely did not contribute to the events, the available evidence precluded a determination of whether effects from the flight instructor’s recent heart attack and underlying heart disease contributed to the circumstances of the accident. In addition, if the flight instructor had experienced a medical event during the flight, should have been reasonable able to control the airplane.

Text from the NTSB. Open the NTSB docket for ERA22FA137 for the full record.