What happened
On May 21, 2016, a single-engine F177RG, registration LN-ALK, was conducting a flight training session at Rakkestad Airport, Åstorp. The flight, operated by Flyklubben Øst, involved an instructor and a student pilot performing various maneuvers, including landing approaches and simulated engine failure drills.
During the third landing attempt of the session, the aircraft approached the runway with the nose gear retracted. As the aircraft touched down, the nose gear failed to extend sufficiently, causing the propeller, nose gear doors, and exhaust pipe to strike the runway surface. The impact caused significant damage to the propeller and airframe components. The aircraft subsequently drifted off the runway onto the grass. Both occupants evacuated the aircraft without injury.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined video footage from airport cameras, which showed the main landing gear extended while the nose gear remained retracted during the final approach. Post-accident testing of the aircraft's landing gear on jacks revealed that while the system functioned correctly under static conditions, a specific sequence could be replicated: if the gear lever is moved upward after the gear is locked, the nose gear retracts before the main gear, leaving the main gear partially unlatched. Furthermore, the investigation identified a malfunction in the landing gear audio warning system, which was found to trigger incorrectly during high manifold pressure settings.
Findings
- The investigation found that the nose gear was not fully extended at the time of touchdown.
- A likely scenario involves an accidental, momentary upward movement of the landing gear lever during the high-workload phase of the final approach, followed by the lever being moved back to the down position.
- The hydraulic system did not show any leaks or mechanical failures during testing.
- A malfunction in the audio warning system prevented the crew from detecting the gear status, as the alert was operating in reverse of its intended logic.
- The crew's ability to notice the error was further hindered by the fact that the warning signal could be easily masked by engine noise when using headsets.