What happened
On 25 January 2010, a Cessna 421C Golden Eagle, registration N1FY, was performing a private visual circuit at Kemble Airfield in Gloucestershire. During the landing sequence, the aircraft's nose gear collapsed immediately upon touchdown. This caused the aircraft to slide along the runway on its nose, coming to a stop just left of the centre line. The impact resulted in damage to both propellers and the underside of the aircraft's nose. The two occupants of the aircraft were uninjured and were able to exit via the rear door. A Flight Information Service Officer monitoring the approach via binoculars observed the landing gear in the down position prior to the incident.
The investigation
Investigators examined the aircraft's landing gear system and its maintenance history. The Cessna 421C utilizes a hydraulic system to extend and retract its tricycle gear. Under normal conditions, the nose gear locks into place after the main gear. However, the investigation established that the nose gear downlock microswitch had failed in the closed position. This failure meant that the cockpit's three green 'down-and-locked' lights remained illuminated even though the nose gear was not mechanically secured.
Engineering analysis of the nose gear actuator revealed that the downlock microswitch was stuck in the closed position due to corrosion. While the aircraft's maintenance programme included annual inspections and biennial sealant replacement to prevent moisture ingress, it was determined that any disturbance to the sealant could have allowed moisture to penetrate the switch.
Findings
- The nose gear failure occurred because the nose gear downlock was not engaged.
- A corroded downlock microswitch on the nose gear actuator provided a false 'down-and-locked' indication to the pilot.
- The failure of the microswitch caused the hydraulic pressure to the gear actuators to be cut off prematurely, preventing the nose gear from locking down.
- The direction of the nose gear leg's travel during the landing sequence likely hindered the gear from locking under its own weight.