History of the Flight
On 11 November 2020, at 07:00 LT, pilots reported to G. V. Bibescu Aerodrome (LRPW) for a briefing regarding a national fox vaccination campaign involving dropping vaccine baits from aircraft. After the briefing, the pilot of aircraft YU-DZZ, together with the vaccine bait launch equipment operator, proceeded to the aircraft. The pilot performed pre-flight checks, started the engine, and verified operating parameters. Takeoff occurred at 08:37 LT.
During climb, the pilot attempted to retract the landing gear but noticed that the three green landing gear position indicator lights were off and the automatic fuse (circuit breaker) for the landing gear electrical control circuit had tripped. Attempts to reset the fuse were unsuccessful.
The pilot contacted the flight coordinator and reported the non-compliant landing gear signaling: the indicator lights were off and the control lever was in the extended position. The pilot then performed a low-level pass by the control tower to visually confirm the landing gear was extended. After visual confirmation from the flight coordinator, the pilot decided to land on runway 08.
After touchdown, the landing gear began to retract slightly until the aircraft's fuselage made direct contact with the runway surface. From the moment of fuselage contact, the aircraft travelled approximately 250 meters before coming to rest at the end of the runway. The two occupants—the pilot and the vaccine bait equipment operator—were not injured.
Aircraft Information
The aircraft was a Piper PA-28RT-201T, serial number 28R-7931159, manufactured in 1992, registered in Serbia as YU-DZZ. The owner was GAS AVIATION d.o.o., and the operator was STS AVIACIJA d.o.o. The aircraft had a valid airworthiness certificate. It was equipped with a retractable tricycle landing gear, hydraulically actuated by an electric reversible pump controlled by a selector on the instrument panel.
The aircraft's interior configuration had been modified in 2015 by installing a vaccine baiting system for fox rabies vaccination campaigns. The modification project, approved by an EASA Part-21 organization, specified removal of the last row of seats, installation of the bait spreading machine in the baggage hold, and seating the operator on the right pilot's seat rotated backward with seat belts. However, the investigation found that the actual configuration differed: the right pilot's seat was removed and replaced with vaccine bait boxes, the equipment was installed in the rear baggage hold, and the operator sat on the floor behind the pilot without seat belts.
Analysis and Cause
The investigation determined that after takeoff, during climb, the pilot found the three green landing gear lights off and the circuit breaker tripped. Despite visual confirmation that the gear was extended, the main landing gear retracted without command during the landing roll. Examination revealed a failure in the electrical control circuit of the landing gear, which caused uncontrolled unlocking of the gear in the extended position. This failure was confirmed by the inability to re-lock the gear safely. The aircraft sustained no important damage due to low-speed fuselage contact. The electrical defect was repaired immediately after the incident, and the aircraft resumed its aerial work missions.
Conclusions
The cause of the serious incident was the failure of the electrical control circuit of the landing gear.