ERA21LA322 · Diamond DA42 L360

The flight instructor and private pilot working towards a multiengine rating reported that during a practice single-engine emergency descent, they received a primary flight display data failure. The student attempted to recover from the rapid descent and despite both of their efforts to apply back pressure on the flight controls, they could not arrest the descent. The flight instructor took over the flight controls and restored power to the engine that had been intentionally shut down; however, he believed that neither engine was producing full power. The descent continued despite their efforts to pull back on the flight controls. An off-airport landing was made in an open field. Postaccident examination and tests of the airplane’s flight control system revealed no evidence of preimpact mechanical malfunctions or failures. Flight control continuity and elevator trim continuity was confirmed, and the full range of movement was observed for all controls. The variable elevator stop system was observed to function without abnormalities when tested. A National Transportation Safety Board (NTSB) airplane performance study found that a rapid descent was entered. However, the data revealed that throughout the loss of altitude in the final minutes of the flight, the rate of descent was arrested, and pitch attitude increased in the final minute of flight before decreasing again. The airspeed throughout the descent likely remained above the aerodynamic stall speed. The investigation was unable to determine any reason why the pilots were unable to recover from the emergency descent. Although the airplane sustained substantial damage to the right wing, the airplane’s nose section, cockpit, fuselage, and empennage sustained minimal damage. The lack of damage to the airplane and an NTSB airplane performance study indicated that the airplane’s pitch likely remained somewhat controllable throughout the descent. The elevator trim position was found slightly nose forward, and neither pilot adjusted the trim wheel to relieve control pressure during their attempts to arrest their descent. It is possible that their lack of action in adjusting the trim wheel contributed to the sensation that they could not increase the pitch of the airplane. The autopilot circuit breaker had been pulled and collared prior to the flight, which also deactivated the electric elevator trim, thus the electric trim did not contribute to the accident.

Verbatim NTSB analysis and probable cause from the NTSB dataset