What happened
On May 7, 2016, a student pilot and an instructor were conducting a series of training flights for UACP qualification near the Aleksandrowice airport (EPBA). The weather conditions were favorable, characterized by good visibility, light turbulence, and a cloud base of 5,000 ft AMSL. During the second series of flights, while the aircraft was on its fourth circuit, the crew was climbing at an indicated airspeed of approximately 150 km/ and an altitude of about 300 m AGL.
At this moment, the left cabin door suddenly opened and the majority of the door structure detached from the aircraft, leaving only a small portion of the frame and hinges attached to the fuselage. The incident occurred over a residential area. Immediately following the separation, the instructor took control of the aircraft and performed a safe emergency landing at the airfield. No injuries were reported.
The investigation
The PKBWL examined cockpit video recordings from the flight, which revealed that while the left door handle was in the closed position, it had not been properly secured. The investigation focused on the door locking mechanism of the Pipstrel Virus 912, specifically the interaction between the handle, the three locking bolts, and the "dead point" required to secure the door.
Investigators found that the mechanism allowed the door to be closed but not locked into a secure state. The study also reviewed the Flight Manual and Maintenance Manual (IUwLiOT) for the aircraft, registration SP-SWWW, to determine if procedures for door security were adequately documented.
Findings
- The primary cause of the incident was performing the second series of flight circuits with the left cabin door closed but not secured.
- The door handle was in a position where the bolts were engaged with the fuselage, but the handle had not been rotated past the "dead point" to prevent accidental unlocking.
- The aircraft's Flight Manual and Maintenance Manual lacked a detailed description of the door locking and securing mechanism.
- There was no warning in the documentation regarding the risk of the handle being accidentally bumped by a pilot's knee during taxiing or flight maneuvers, which could inadvertently unlock the door.
Safety action
- The manufacturer is recommended to update the Flight Manual (Chapter 7) to include a description of the door locking and securing mechanism.
- The Maintenance Manual (Chapter 8) should be updated to include specific checks of the door locking mechanism during cabin inspections.
- The pre-flight checklist should be amended to explicitly require verifying that the doors are "CLOSED-SECURED" rather than simply "CLOSED".