What happened
On 28 February 2000, a Piper PA-3/4-200T, registration G-BOSD, was engaged in a training flight for an instrument rating examination at Exeter Airport. Following the successful completion of the flight, the aircraft was taxiing from the apron toward the runway holding point for a second flight detail. During this taxiing phase, the nose landing gear collapsed immediately after the nosewheel struck a taxiway light. The impact caused significant damage to the nose cone, gear doors, and the nose landing gear itself. Additionally, the engines were shock loaded, and both propellers sustained damage.
There were no injuries to the two crew members on board.
The investigation
Investigators noted that this was a recurring issue for this specific aircraft, which had suffered a nearly identical nose gear collapse at the same airport on 19 June 1999. Following that previous incident, the drag brace assembly had been replaced with new components sourced from the manufacturer. Testing of the new assembly showed that the over-centre measurement was within the manufacturer's allowable limits.
To understand the mechanism of the failure, investigators used a similar aircraft, a Piper Seneca III, on jacks. They discovered that while the drag brace could not be unlocked by hand alone, vigorous shaking of the nose gear—simulating the impact of a taxiway light—could move the brace by up to 1/8 inch. When the aircraft's weight was applied to the gear, even light hand pressure was sufficient to move the brace into the unlocked position. The investigation concluded that the geometry of the nose gear allows ground static loads to apply forces that tend to retract the gear.
Findings
- The collapse was triggered by a combination of vertical acceleration and fore-and-aft loading on the nose wheel, specifically when the aircraft bumped over a taxiway light.
- The drag brace moved from its locked position due to the application of specific loading patterns during taxiing.
- The down-lock spring link provided relatively low resistance, exerting only about 2 to 3 lb of force, which was insufficient to prevent movement under the identified loading conditions.
- The natural tendency of the nose gear to retract was able to overcome the hydraulic extension loads once the brace moved out of the over-centre position.