What happened
On August 29, 2019, a PA-2able-28RT-201T, registration SP-GME, was conducting a commercial pilot license (CPL) examination flight. The crew, consisting of a flight instructor acting as an examiner and a student pilot, departed from Mielec for a flight involving maneuvers at Krosno Airport (EPKR).
During the third circuit at Krosno, the instructor simulated an engine failure by reducing power to idle. As the student pilot managed the simulated emergency, the landing gear lever was moved to the down position. The crew believed the landing gear was properly extended because the green indicator lights were illuminated. However, during the approach to runway 11R, the crew felt slight vibrations, which they initially interpreted as shimmy. Upon realizing the issue, the instructor took control, increased power, and executed a go-around.
During the climb, the pilot noticed a blown fuse for the landing gear lights. After returning to Mielec, a post-flight inspection revealed that the tips of three propeller blades had been bent and scraped by approximately 12 centimeters. No injuries were reported, and the engine remained undamaged.
The investigation
The PKBWL investigation focused on why the landing gear failed to extend despite the visual indication of success. Technical examination of the aircraft's electrical system revealed a loose wire end near the flap microswitch. This loose wire was contacting the airframe, creating a short circuit in the landing gear warning system signaling circuit.
This short circuit occurred specifically when the throttle was set to idle, which triggered the microswitch. The resulting short circuit blew the 5A "Landing gear/lights" fuse and simultaneously cut power to the three green landing gear indicator lights. Consequently, the crew was misled into believing the gear was down when it had not actually locked into place.
Findings
- A loose electrical wire caused a short circuit that prevented the landing gear lights from providing accurate status information and blew the relevant fuse.
- The instructor failed to properly monitor the student pilot's actions during the simulated engine failure, specifically failing to verify the landing gear extension.
- The student pilot was likely focused on managing the simulated emergency, which, combined with the misleading cockpit indications, led to the undetected gear malfunction.