What happened
On July 21, 2025, an Aero Vodochody L-39C jet trainer, registration N339L, was conducting an instructional flight from Watertown Regional Airport to Oshkosh when it experienced an engine failure. The flight was being conducted by a flight instructor in the front seat and a pilot receiving instruction in the rear seat.
During the climb through flight level 200, the crew reported an odor inside their oxygen masks followed by smoke entering the cockpit. The instructor depressurized the aircraft, which cleared the smoke, but the engine could not be restarted using the auxiliary power unit. The aircraft began a descent, and the instructor initially attempted to reach Southwest Minnesota Regional Airport before deciding to divert to Granite Falls Municipal Airport.
While performing a right descending turn toward the runway, the instructor determined the aircraft would not reach the pavement and instructed the student to eject. The instructor successfully ejected from the front seat and landed via parachute, sustaining serious injuries. The student pilot, seated in the rear, did not eject and was fatly injured when the aircraft impacted a berm near railroad tracks. The upper portion of the aircraft's vertical stabilizer struck a power line prior to the impact.
The investigation
Investigators examined the Ivchenko AI-25TL turbofan engine and found that a stick was wedged between the inlet guide vanes and the first-stage compressor blades. The compressor/low-pressure spool was seized and could not be rotated manually. Additionally, the low-pressure turbine rotor blades and nozzle vanes exhibited thermal damage, with some components partially consumed.
At the crash site, a strong smell of Jet-A fuel was present, and fuel was observed leaking from the wing tip tanks and fractured fuselage lines. The aircraft's nose and cockpit sustained heavy crushing deformation. Due to the damage to the rear ejection seat and its firing mechanism, bomb squad personnel were required to use a controlled detonation of C4 explosive to safely separate the student pilot from the seat.