What happened
On 27 September 2005, a Piper PA-34-200T Seneca II, registration N43GG, was performing a private flight to Humberside Airport. During the approach, the pilot deployed the landing gear, and the cockpit indicators confirmed that all three units were down and locked. The aircraft touched down on its main wheels with the nose raised. However, as the pilot lowered the nose to the runway, the nose landing gear collapsed.
The aircraft continued along the runway for approximately 120 metres before coming to a halt. The impact caused both propellers to strike the runway, resulting in severe damage, and also damaged the nose cone and nose landing gear doors. The pilot and passenger were able to exit the aircraft safely and sustained no injuries.
The investigation
An engineering examination of the nose landing gear was conducted at Humberside Airport. Investigators found that while the cockpit microswitch indicated a 'down and locked' status, the gear was actually in an unlocked, under-centre condition. The investigation focused on the drag link assembly and the downlock spring link.
Technical analysis revealed significant distortion to the central pivot pin that secures the spring lock. Additionally, the pin slot in the spring link showed ovality. These findings suggested that the mechanism had lost its ability to maintain the gear in a secure, over-centre position, allowing the gear to retract under the load of the landing.
Findings
- The nose landing gear failed to maintain a locked state despite the cockpit indicators showing it was secure.
- The collapse was caused by the geometric locking mechanism becoming ineffective.
- The distortion of the central pivot pin and the ovality of the spring link pin slot likely allowed the drag link assembly to move into an unlocked position.
- It is probable that a combination of in-service wear and a previous high-load event, such as a heavy landing, caused the mechanical degradation of the downlock components.