What happened
On July 29, 2016, a private flight involving a DG-1000M glider, registration HB-2481, was conducting a series of self-launching operations at Buochs Airfield (LSZC). The flight plan involved a self-launch, a landing, and an immediate subsequent self-launch. The purpose of the landing was to demonstrate the engine-extension procedure to a passenger, who was a local air traffic controller.
During the approach, the pilot observed a green light on the instrument panel. However, this was the upper green light, which indicates that the landing gear is retracted and locked. After deploying the air brakes during the final approach, the pilot's attention was focused outward on the runway, and no further verification of the gear position was performed. The aircraft touched down with the tailwheel first, followed immediately by the underside of the fuselage. The impact was only slightly more forceful than a standard landing, but the aircraft slid along the runway on its fuselage until it came to a halt. The landing resulted in light injuries to the passenger and light damage to the aircraft's fuselage.
The investigation
The investigation focused on the cockpit instrumentation and the pilot's monitoring procedures. It was established that the aircraft's landing gear indicator system utilizes two identical green lights. The lower light illuminates when the gear is extended, while the upper light illuminates when the gear is retracted and locked. The investigation also noted that the pilot had set the navigation computer's volume to a low setting due to frequent warnings, which meant no audible alerts were heard during the flight.
Findings
- The pilot misidentified the landing gear status by observing the upper green light (indicating retracted gear) as the indicator for extended gear.
- The pilot failed to perform a positive verification of the landing gear position during the final approach after deploying the air brakes.
- The aircraft's landing gear was not extended at the time of touchdown.
- The pilot's attention was diverted from the cockpit instruments to the runway environment during the final stages of the approach.