Incident Overview
On 3 January 2020 at 12:22 UTC, a Mooney M22 Mustang, registration HB-DVY, landed with its landing gear retracted at Portorož Airport, Slovenia. The aircraft slid approximately 300 meters along the runway and came to a stop 400 meters before the runway end. Both pilots exited the aircraft, which was subsequently secured by airport fire services and Portorož Airport staff. The cabin was sealed by police, and the aircraft was moved to a hangar for examination. No injuries were reported. Damage included the propeller, engine, fuselage, and runway surface.
Flight History
The aircraft departed Switzerland for a 1-hour 43-minute VFR flight. It entered Slovenian airspace at point UMBEK at 4,500 feet and descended to 1,000 feet AGL in coordination with air traffic control. Weather at the time was: light west wind, visibility 8,000 meters, no cloud (METAR LJPZ 031230Z 28003KT 8000 NSC 10/7 Q1026). The pilot reported visibility over sea between 5 and 10 kilometers with slight haze. The approach was high and fast, with a steeper-than-normal descent. The pilot extended flaps to 30 degrees, moved the landing gear lever to DOWN before final, and continued flap extension to landing position. Speed was approximately 125 mph with throttle idle. The aircraft stabilized on final approach to runway 33.
Investigation Findings
Interviews with both pilots revealed that they had performed a landing gear check (called a "Fance check") before touchdown, including verifying the gear indicator lights and lever position. After landing, they heard the gear warning horn and saw an orange gear unsafe light. The passenger (also a pilot and aircraft owner) found the 10-amp LANDING GEAR CONTROLS fuse pulled in the fuse panel. The fuse box has a cover; the fuses are not visible when closed. The pilots had inspected fuses during flight but had not observed any issue at that time.
Examination of the electrical system showed three fuses: LANDING GEAR ACTUATOR, LANDING GEAR CONTROLS, and LANDING GEAR WARNING. The LANDING GEAR CONTROLS fuse was found pulled; its removal requires considerable force, making involuntary ejection unlikely. The pilot noted that the gear lever force felt heavier than normal. Both pilots used active noise-cancelling headphones (BOSE A20). The warning horn is activated when throttle is reduced below 15 inches manifold pressure. The pilots did not distinguish the warning sound from other noise due to engine operation and headphone characteristics.
Conclusions
The investigation concluded that a fault on the worn-out 10-amp landing gear control fuse caused it to trip, leaving the gear retracted after the lever was moved down. The green landing gear indicator light was likely misread due to sunlight behind the aircraft, causing both pilots to interpret it as lit. The indicator light intensity is manually adjustable, but even at maximum, daytime visibility is poor. Weather conditions were not a significant factor but may have contributed due to limited visibility at an unfamiliar airport. ATC audio recordings captured the warning sound, but there was no time for controller intervention. After repairs and testing, the aircraft was returned to service with properly functioning landing gear.
No safety recommendations were issued. The report was to be presented at safety conferences and published in the safety bulletin to highlight hidden technical issues, adverse effects of active noise-cancelling headphones, and proper gear indication awareness.