What happened
On 19 March 2008, a Challenger CL-600-2A12, registration C-FURG, was performing an instrument flight rules mission from Bonaventure Airport, Quebec, to Québec/Jean Les to transport medical patients. During the approach to Québec, the flight crew observed that the nose gear failed to extend. After a low fly-pass confirmed the anomaly to the tower and maintenance personnel, the crew attempted to cycle the gear and activate the manual release handle twice, but the gear remained retracted. The crew prepared the six passengers for a landing with the nose gear up, and at 0643 EDT, the aircraft landed on its nose. There were no injuries to the passengers or crew.
The investigation
The investigation focused on why the nose gear failed to deploy despite manual intervention. Upon recovery, the nose wheel oleo pneumatic shock absorber was found to be flat. The investigation established that the right gravel deflector, part of a specialized kit for unpaved runway operations, had become stuck in the nose landing gear well. This blockage prevented the gear from extending.
Technicians examined the oleo strut and found that while the hydraulic oil level was correct, there had been a complete loss of nitrogen pressure. While the exact cause of the nitrogen leak could not be replicated, evidence suggested the leak likely occurred through the second filler valve nut. The investigation also noted that the aircraft's configuration, including the gravel deflectors, significantly reduced the clearance within the gear well.
Findings
- The loss of nitrogen pressure in the oleo pneumatic shock absorber caused the strut to compress.
- This compression allowed the nose landing gear to shift out of the uplock latch, causing the wheel assembly to pivot.
- The resulting movement caused the right gravel deflector to become jammed within the nose landing gear well, physically preventing the gear from extending.
- The design of the landing gear latch and pin allows the gear to drop into the well if the strut compresses, creating a risk of the deflector obstructing the deployment sequence.
- The narrow clearance between the gravel deflectors and the well structure makes the aircraft vulnerable to similar failures if the oleo strut loses pressure.