CEN21LA035 · Piper PA28 140

The flight instructor and his student were departing on an instructional flight from a private grass airstrip. The pilots completed a before-takeoff engine runup with no anomalies or malfunctions reported. The flight instructor reported that his student performed the soft-field takeoff. After the airplane became airborne, the student reduced airplane pitch to remain within ground effect, and allowed the airspeed to increase to 80 knots. The flight instructor reported that during the initial climb there was a drop in engine speed (rpm). The flight instructor confirmed the throttle control was full forward, but there was “no significant engine performance.” The flight instructor took control of the airplane from his student, reduced pitch, and banked to avoid the highway and powerlines located at the end of the airstrip. The flight instructor stated that a lack of engine performance resulted in a forced landing before the airplane completed 90° of turn from the takeoff heading. The airplane landed on the northside of the highway, collided with a power pole, and came to a stop. The airplane’s left wing and engine mount were substantially damaged during the accident.

According to the flight instructor, the airplane’s flaps were extended 10° for the soft-field takeoff based on a laminated checklist in the cockpit. The airplane’s owner’s handbook requires the flaps to be extended 25° for a soft-field takeoff. However, according to the flight instructor, the airplane became airborne and accelerated to a safe airspeed before it climbed out of ground effect. As such, the incorrect flap extension likely did not contribute to the accident.

Postaccident engine examination revealed low cylinder compression and an oil-fouled lower spark plug for the No. 1 cylinder. Otherwise, the examination did not reveal any anomalies. The engine was subsequently started and run several times without any issues; however, the engine was not accelerated to maximum static rpm during the examination due to a damaged engine mount and the airplane being supported on jack-stands.

The flight instructor reported a decrease in engine rpm during initial climb out of ground effect. Although engine performance would be diminished by a low cylinder compression and an oil-fouled lower spark plug for the No. 1 cylinder, those discrepancies would not result in a sudden loss of engine rpm during flight. As such, the low cylinder compression and/or oil-fouled spark plug likely did not result in the reported decrease in engine rpm as described by the flight instructor.

The temperature and dewpoint at the time of the accident were in the range of susceptibility for the formation of serious carburetor icing at glide power. Although a formation of carburetor ice before takeoff could have resulted in a sudden decrease in engine rpm, the pilots completed a before-takeoff engine runup with no anomalies or malfunctions reported.

The reason for the partial loss of engine power could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset