What happened
On 31 October 2023, an ATR 72-212 A, registration G-CMJM, was performing a commercial passenger flight departing from Edinburgh Airport. During the takeoff roll on Runway 06, the right nose landing gear wheel detached from the aircraft. The loss of the wheel was not immediately detected by the flight crew, nor was it noticed by the airfield operations department, as the component moved off the side of the runway surface.
The flight continued to Belfast City Airport without any abnormal performance or indications of a mechanical issue. The crew only became aware of the missing equipment after the aircraft had parked at its stand and ground personnel notified the commander. Following the discovery, inspections were conducted at both Edinburgh and Belfast; the detached components were located near the runway at Edinburgh.
There were no fatalities and no injuries among the 4 crew members or 5 and 55 passengers on board.
The investigation
The AAIB investigation focused on the fractured nose landing gear axle and the condition of the wheel assemblies. Examination of the right nosewheel revealed that the assembly had been put together with all tie bolts loose. Investigators found an unauthorized interposition product between the mating faces of the two half-wheels, which is prohibited for this component type as it can cause the tie bolts to loosen. Additionally, the bearings showed evidence of being over-greased, and no balancing weights were fitted to the assembly.
Similar issues were noted on the left nosewheel, including loose tie bolts, the use of the incorrect interposition product, and over-greasing of the bearings. Metallurgical analysis of the failed axle indicated that the fracture was caused by a combination of thermal shock and cadmium liquid metal embrittlement, both resulting from extreme heat.
Findings
- The right nosewheel detached because the axle fractured due to bearing overheat.
- The overheating was driven by several contributing maintenance non-conformances, including the use of an unauthorized interposition product, over-greasing of the bearings, and the absence of wheel balancing weights.
- The failure of the axle was specifically attributed to the thermal shock and liquid metal embrittlement caused by the intense heat generated during the bearing failure.