History of the Flight
On 27 September 2005 at 1438 hrs, a Piper PA-34-200T Seneca II, registration N43GG, was on approach to Humberside Airport, Ulceby, South Humberside. The pilot selected the landing gear down and observed three green lights on the position indicator, indicating all units were down and locked. After a normal approach, the aircraft landed on its main wheels with the nose raised. As the pilot lowered the nose, it continued to fall smoothly until the nose landing gear (NLG) collapsed. The aircraft continued along the runway on its main landing gear and nose fairing for approximately 120 m before coming to a halt. Both pilot and passenger were unhurt and exited the aircraft prior to the arrival of the airport fire service. The propellers contacted the runway and were severely damaged; the nose cone and nose landing gear doors were also damaged.
Aircraft and Pilot Information
The aircraft was a 1976 Piper PA-34-200T Seneca II, powered by two Continental TSIO-360-EB piston engines. The flight was private, with one pilot and one passenger on board. The pilot held a UK Private Pilot's Licence and had 470 hours total flying experience, including 119 hours on type. The aircraft had previously suffered an NLG collapse on 8 May 2003, when registered as G-ROLA, and was repaired per New Piper Aircraft Inc recommendations, including replacement of the downlock spring link. After functional checks, it was declared serviceable. The aircraft was sold and transferred to the US register on 25 June 2004, with no reported landing gear issues from acquisition to the accident.
Nose Landing Gear Mechanism
The NLG is a forward-retracting type, held in the down position by a geometric downlock mechanism. When extended and under load, the drag link assembly prevents collapse. The downlock spring link maintains the drag links in the over-centre locked position. Small dimensional changes in the spring link can allow the drag link assembly to remain unlocked while the cockpit indicator shows a locked condition.
Examination and Analysis
Examination of the aircraft at Humberside Airport, with the NLG secured in the down position, revealed the extension link was in the down and locked position, and the microswitch had activated. However, the drag link assembly was in an unlocked, under-centre condition. The downlock spring link showed ovality in its pin slot, and the central pivot pin was severely distorted. The retraction jack appeared in good condition. Analysis indicated that the NLG had not achieved a locked condition despite the indication, leading to collapse as weight was applied. The distortion of the centre pivot pin and ovality likely resulted from a high load event, such as a nose wheel landing or rough surface takeoff, though no such event was identified in records.
Conclusions
The NLG failed to maintain a locked condition despite indicating it was down and locked. A change in geometry of the drag link spring lock, probably due to a combination of a high load event and in-service wear, prevented the drag link assembly from achieving or sustaining a safe over-centre condition, allowing the NLG to collapse under load.