Accident Summary
On 22 February 2003, a Piper PA-34-200T Seneca II, registration G-BNEN, was departing on a passenger flight from White Waltham Airfield to Cambridge. During the takeoff roll on the grass runway, at approximately 50 kt, the nose began to drop. The pilot could not counteract the pitch with elevator and realized the nose landing gear had retracted. Throttles were closed, but both propellers had already struck the runway. The aircraft slid to a halt supported by the main gear and the underside of the nose and engine cowlings. The pilot reported no unusual noises prior to the incident. No injuries occurred among the one crew and one passenger.
Investigation Findings
Examination revealed the nose landing gear had collapsed. The threaded stem of the upper eye-end of the sprung downlock link had bent and fractured. The slot in the downlock link was crushed and distorted by the cross-pin, indicating a high compressive load. Considerable wear was found in the upper and centre pivot joints of the drag brace. The upper joint, attaching the drag link to the landing gear leg, was the most severely worn. The steel sleeve and bronze bush at this joint showed bell-mouthed and oval wear, with clearances exceeding specified limits for the sleeve. The centre joint also exhibited moderate wear on the bronze bush of the upper link element, primarily on the left side. The lower joint showed little wear. The over-centre dimension of the drag link assembly measured 0.310 inch, greater than the specified minimum.
Maintenance History
Ten days before the accident, the aircraft underwent a 50-hour check. A fault had been reported: during emergency (free-fall) extension, the nose gear did not indicate down and locked, though normal hydraulic extension worked. Maintenance confirmed the downlock link was slightly too long, preventing the retraction spring from pulling the retraction link onto the downlock stop. After lubricating the mechanism, the downlock link was shortened by a small amount, enabling free-fall extension. Free play at the drag link centre stops was not considered excessive. An FAA Airworthiness Directive (93-24-12) requiring renewal of the upper drag link forward pivot bolt every 500 flight hours had been complied with about 200 flight hours earlier. The aircraft had 6,950 total hours and was used regularly for charter work, including six recent grass operations at White Waltham without issue.
Probable Cause
The nose landing gear collapse is strongly linked to the recent adjustment of the downlock link, combined with the failure of its upper eye-end, and the significant wear in the upper and centre pivot joints of the drag brace. The adjustment was made to correct an inability to lower the gear by free fall, but no procedure for such adjustment was available in the aircraft maintenance manual.