What happened
On 30 September 2010, a Bombardier DHC8-311 (Q300) operating a scheduled service from Wellington to Nelson diverted to Woodbourne Aerodrome due to adverse weather conditions. The aircraft was carrying 43 passengers and a crew of three.
During the flight, the crew attempted to deploy the landing gear. While the main landing gear legs extended as expected, the nose landing gear failed to reach its fully extended position. This malfunction was likely caused by debris within the hydraulic fluid obstructing a small orifice in the nose gear actuator.
Initial cockpit indications correctly signaled that the gear was "unsafe," noting that the nose gear was not locked and the forward doors were open. However, when the crew consulted an independent verification system, it displayed three green lights, falsely suggesting all gear was locked. Believing a sensor was simply malfunctioning, the pilots proceeded with the approach. During the final approach, both the landing gear warning horn and the ground proximity warning system alerted the crew to the unsafe gear status. The crew dismissed these aural alerts, maintaining their belief that the sensors were faulty. Upon touchdown, the nose gear was forced into the wheel well, causing the aircraft to skid on the nose gear doors. The 46 people on board escaped with no injuries, and the aircraft sustained only minimal damage.
The investigation
The investigation examined the mechanical failure of the nose gear and the reliability of the aircraft's monitoring systems. Investigators determined that the primary landing gear indication system had functioned correctly by reporting the unsafe status. However, the secondary verification system provided misleading information that led the crew to believe the gear was secure. The inquiry also looked into previous incidents involving the same nose gear in the weeks prior, which were likely caused by the same hydraulic debris issue but had not been properly diagnosed.
Findings
- The nose landing gear failed to extend fully because debris in the hydraulic fluid blocked an orifice in the actuator.
- The independent landing gear verification system was unreliable and provided false positive indications.
- The pilots failed to heed the landing gear warning horn and the ground proximity warning system during the final approach.
- The crew's decision to continue the landing was based on an incorrect assumption that the primary system was faulty rather than the verification system.
Safety action
While the operator and the manufacturer implemented several safety measures, the Commission identified a persistent safety issue regarding the reliability of the verification system. Consequently, a recommendation was made to the Director of the New Zealand Civil Aviation Authority to coordinate with Canadian authorities to ensure the manufacturer improves the reliability of the landing gear verification system.