N906ER

On August 9, 2021, about 1335 eastern daylight time, a Diamond Aircraft DA-42-L360 airplane, N906ER, was substantially damaged when it was involved in an accident near Hiddenite, North Carolina. The flight instructor and private pilot were not injured. The airplane was operated by Academy of Aviation as a Title 14 Code of Federal Regulations Part 91 instructional flight.

The flight instructor and private pilot had completed several maneuvers and simulated emergency procedures during the multiengine instructional flight. Following a simulated single-engine approach and landing into Wilkes County Airport (UKF), North Wilkesboro, North Carolina, the instructor attempted to simulate a right-engine failure during the takeoff roll; however, the engine lost power. The instructor restarted the right engine and performed a “quick run up” on the runway in which “everything was functioning normally.” The student continued the takeoff and climb.

Upon reaching 5,000 ft mean sea level (msl), the student performed an emergency descent maneuver while also simulating a left engine fire. As part of the simulated left engine fire, the left engine was shut down with the full reduction of the throttle, propeller, and mixture. During the maneuver after descending about 500 – 1000 ft, the Attitude and Heading Reference System (AHRS) failed, and the flight instructor directed the student to recover “gradually and easily” at 3,500 ft msl and maintain 90 knots. The AHRS displayed a message that it was aligning/ calibrating and to keep the wings level.

The flight instructor subsequently noticed that airspeed had increased through 100 knots and altitude had decreased to about 3,000 ft, and about this time, the student stated, “I can’t pitch up” and then the sole operating right engine began to sputter.

The flight instructor took the flight controls and, on both engines, applied full-forward mixture, propeller, throttle, and ensured the landing gear and flaps were up; however, he was unable to increase the pitch and stop the descent as well. The flight instructor noticed that the manual elevator trim was near the takeoff position. Neither the flight instructor, nor student, adjusted the elevator trim in the descent.

The flight instructor reported that “it felt as if we were unable to fully pull the control stick back, as if it were restricted preventing full movement.” He added that both engines regained power, however, it felt as if they “were not producing normal operation power.” He reported that the airspeed increased to over 100 knots during the descent, so he reduced power, and turned toward an open field.

Throughout the descent, the flight instructor reported that “We both were pulling back as hard as we could but could not get the nose to come up.” About 500 ft above ground level, the flight instructor kept his hands on the control stick and the student moved the landing gear down and added full flaps for landing. Subsequently, the airplane touched down in an open soybean field, impacted a ditch, and skidded to a stop. During the landing, the nose gear collapsed, and the right main landing gear partially collapsed, which resulted in substantial damage to the right wing.

Postaccident examination of the airplane and engines revealed no evidence of preimpact mechanical malfunctions or failures.

Flight control continuity was established from the flight controls to each control surface, which moved freely and correctly through the full range of motion.

The manual elevator trim wheel indicated a slight nose down setting. The autopilot circuit breaker was found pulled and collared. When electrical power was turned on, the electric elevator trim switch did not move the elevator trim as expected.

According to the airplane flight and maintenance manual, the airplane was equipped with a variable elevator stop system which is an electrically operated actuator that limits the elevator up travel depending upon engine and flap settings. This system was evaluated according to the operational test in the maintenance manual and no abnormalities were observed with the flight controls.

An NTSB airplane performance study was performed utilizing automatic dependent surveillance-broadcast (ADS-B) data and weather modelling. Review of the data in the final few minutes of the flight found that a rapid descent was initiated from about 5,000 ft msl. Within the initial phase of the descent, the airplane pitched down 30° and banked right to about 45°. A maximum of about 155 knots indicated airspeed and a 6,000 foot per minute descent was obtained before a momentary leveling off was observed. The descent then continued but at a lower rate.

Within the final minute of data, the pitch increased to about a positive 5° angle, which was followed by a pitch down of about 10°. Subsequently, airspeed increased from about 80 knots to about 140 knots and the descent rate reached 4,000 feet per minute (fpm). Within the final 20 seconds of data, airspeed decreased rapidly from about 140 knots to a minimum observed 70 knots, the rate of climb increased momentarily to 1,000 fpm, and pitch increased to positive 10° before decreasing to negative 5° near the end of data. The airspeed throughout the descent likely remained above the aerodynamic stall speed.

A weight and balance calculation performed by the operator found that the airplane was within the normal envelope range.

An attempt was made to download flight data from the Garmin G1000 SD cards installed, however, no data had logged to the cards.