What happened
On May 15, 2023, a Learjet 35A operated by a German aviation company crashed at the Hohn military airfield during a training flight. The flight was intended to serve as a proficiency check for the pilot in command, involving simulated instrument approach procedures to Wunstorf.
Shortly after takeoff from runway 26, the crew initiated a simulated failure of the right engine. While the aircraft initially maintained its climb, the pilot was unable to sufficiently counteract the resulting asymmetric thrust. The aircraft began to yaw and roll heavily to the right, losing altitude and airspeed. Witnesses observed the aircraft performing a broken roll before plunging steeply at the end of the runway, where the impact resulted in an explosion. Both pilots on board were killed, and the aircraft was destroyed.
The investigation
The BFU examined the flight data recorder (FDR) and cockpit voice recorder (CVR) to reconstruct the sequence of events. The investigation focused on the lateral control of the aircraft during the engine failure simulation. Investigators analyzed the rudder control mechanics and the physical environment of the cockpit.
Notably, the investigation looked into the possibility of physical obstructions in the cockpit. Previous reports from the same operator indicated that air conditioning wiring in the left footwell could interfere with full rudder pedal travel if the pilot's foot was positioned incorrectly. The BFU also reviewed the aircraft's aerodynamic characteristics, noting that this specific aircraft lacked Avcon Fins, which are used to enhance directional stability.
Findings
- The primary cause of the accident was insufficient rudder pedal input to compensate for the asymmetric thrust following the simulated engine failure.
- This lack of corrective rudder caused a large sideslip angle, leading to a stall of the vertical stabilizer and the wing, which induced the uncontrolled roll.
- The investigation could not definitively determine why the rudder input was insufficient, though the physical possibility of footwell obstructions was noted.
- High cockpit workload contributed to the event, as the tower frequency was heavily congested with other aircraft, leading to fragmented communication during critical checklist items.