What happened
On 3 March 2011, a DHC-8-402 Dash 8, registration G-JEDR, was performing a commercial passenger flight departing from Exeter Airport. During the takeoff roll on Runway 08, a single audio signal was noted between 80 kt and V1/VR. As the landing gear was retracted following a positive rate of climb, the inboard wheel of the right main landing gear separated from its axle and fell to the ground near the airport boundary.
Passengers on the right side of the aircraft observed sparks and the subsequent loss of the wheel. The flight crew entered a holding pattern east of the airport to evaluate the situation. An onboard engineer assisted the crew in assessing the gear, noting that while the gear appeared locked, parts of the mechanism were protruding. The crew decided to use a left-wing-down landing technique, ensuring the left mainwheel touched down first to mitigate the risk of the right gear collapsing. The aircraft landed safely, though it veered to the left upon touchdown, requiring significant rudder input to maintain the centerline.
The investigation
The AAIB examined the detached wheel, the axle, and the remains of the failed bearings. The investigation found that the wheel nut remained correctly installed with its locking devices intact. Examination of the right main landing gear door revealed damage caused by contact with the rotating wheel assembly.
Investigators also reviewed the flight data recorder and cockpit voice recorder. While the cockpit voice recordings confirmed the crew's account of the emergency, the latter portion of the recording was lost because the aircraft's electrical power was not isolated immediately after the incident, allowing the CVR to be overwritten.
Findings
- The investigation established that the outer wheel bearing suffered a trapped cage, which led to a catastrophic failure.
- This failure caused the outer bearing cone to deform, which subsequently allowed the inboard wheel to detach from the axle during the landing gear retraction sequence.
- The specific trigger for the cage becoming trapped—whether due to wear, improper torque, or external shocks—could not be definitively determined.
Safety action
Following the incident, several safety measures were initiated:
- The operator's engineers will receive updated training on bearing inspection and maintenance techniques.
- The bearing manufacturer has instructed its production departments to ensure that the cage clearance on these specific bearings remains close to the low end of the manufacturing tolerance.
- The operator has reminded flight crews of the necessity to pull the CVR/FDR circuit breakers following an incident to prevent the loss of critical flight data.