What happened
On May 27, 1999, a Beechcraft Bonanza A36, registration HB-EWU, was performing a private VFR flight returning to Zurich Airport from Gerona. During the downwind leg for runway 28, the pilot attempted to extend the landing gear at approximately 100 mph, but the cockpit indicator remained red, signaling that the gear had not locked down.
After a second unsuccessful attempt, the pilot entered the Embrach holding pattern. In an effort to resolve the issue, the pilot instructed a passenger to use the manual emergency extension system. The passenger attempted to turn the hand crank, but the mechanism eventually blocked. Uncertain of the gear's position, the passenger then rotated the crank in the opposite direction until another stop was reached. During this process, the pilot moved the gear selector to the 'RETRACT' position, which caused the gear to retract entirely, according to observations from the control tower.
With no further options and the gear retracted, the pilot prepared for a belly landing. The aircraft touched down on runway 28 at 11:37 local time. The landing was controlled, and although the aircraft sustained significant damage to the fuselage underside, flaps, and propeller, all six occupants escaped without injury.
The investigation
The investigation examined the aircraft's maintenance history and the mechanical state of the landing gear system. While recent inspections had found the gear system to be functional, investigators discovered that the manual hand crank was deformed from being turned in the direction of retraction.
Upon disassembly of the landing gear actuator, investigators found a broken internal spring in the sector gear stop assembly. This finding aligned with manufacturer guidance stating that improper rigging can cause the actuator to strike internal stops, potentially jamming the entire system. Additionally, a previous maintenance entry from October 1998 had noted intermittent issues with the gear warning light and blown fuses.
Findings
- The primary cause of the incident was a probable malfunction within the landing gear system, the specific trigger for which could not be definitively determined.
- The emergency manual extension was handled ineffectively; the pilot did not verify if the passenger's manual cranking was being performed according to the correct direction specified in the flight manual.
- The manual extension mechanism was not ergonomically designed, contributing to the difficulty of the emergency procedure.
- The landing gear was inadvertently retracted during the attempt to troubleshoot the malfunction, as the checklist explicitly prohibits manual retraction of the gear.