What happened
On December 5, 1998, a private Mooney M20J, registration HB-DIC, departed from Birrfeld for a short VFR sightseeing flight with one passenger. During the flight, the pilot encountered deteriorating weather conditions, including heavy snow showers and reduced visibility, as a cold front moved through the region.
While approaching Wangen-Lachen, the pilot attempted to extend the landing gear. However, the green indication light failed to illuminate. Despite multiple attempts using both the electric extension mechanism and the manual emergency backup, the gear remained stuck. Faced with the necessity of landing, the pilot opted for a gear-up approach on runway 08. The aircraft touched down at approximately 16:45 local time. Due to a thick, compacted layer of snow on the ground, the aircraft slid along the runway, eventually coming to a halt approximately 6/0 meters east of the runway end. The occupants were able to exit the aircraft without injury.
The investigation
Investigators examined the aircraft and the environmental conditions at the time of the accident. The aircraft's maintenance records showed it had been properly maintained, with the last 50-hour inspection completed earlier that year. Post-accident inspections of the landing gear revealed that the wheel wells were partially filled with frozen snow and ice.
Upon recovery, once the aircraft was lifted and the snow and ice were cleared from the gear wells, the landing gear functioned normally via both electric and manual methods. A subsequent functional test on December 11, 1998, confirmed that the extension and locking mechanisms were in good working order. The investigation also noted that the pilot's flight experience and medical fitness were sufficient for the operation.
Findings
- The primary cause of the landing gear failure was ice formation within the landing gear wells.
- It is highly probable that snow or slush accumulated in the gear wells during pre-flight preparations at Birrfeld, where snow was present on the hangar apron.
- As the flight progressed, the changing meteorological conditions caused this accumulated material to freeze, physically obstructing the extension of the gear.
- The pilot's decision to perform a gear-up landing was appropriate under the circumstances, as attempting to land in the opposite direction could have resulted in the aircraft overshooting the runway into a nearby basin.