UK investigators believe bearing overheat led to a nose-wheel being shed from an ATR 72-500 on departure from Edinburgh in October 2023, but the reason behind the failure could not be determined.
The Emerald Airlines aircraft – with 55 passengers and a crew of four – continued to Belfast City, where it landed safely, with the pilots unaware that the right-hand wheel had detached.
According to the UK Air Accidents Investigation Branch, the missing wheel was located off the left side of Edinburgh’s runway 06.
Examination of the aircraft (G-CMJM) showed the nose-gear axle had sheared off and showed signs of heat damage.
The turboprop’s nose-gear wheels had been changed during line maintenance 20 days beforehand, on 11 October 2023.
But the inquiry says “no issues” were reported in relation to the nose-gear in the sectors before the 31 October occurrence. Emerald operates regional services on behalf of Aer Lingus.
Investigators discovered the right-hand wheel had no balancing weights in the half-wheel sections, a fracture in the hub, and had evidence of over-greased bearings.
The inquiry also found an “interposition product” between the half-wheel faces – pointing out that this product was “not allowed” because it could lead to tie-bolt loosening. All the tie-bolts on the wheel assembly were loose.
Similar issues were found on the remaining left-hand nose-wheel.
Investigators believe the axle fractured as a result of overheating of the bearing in the wheel, causing a combination of thermal shock and liquid cadmium embrittlement.
The inquiry could not positively determine the reason for the overheat, but inspection of the components indicated several possible contributors – including over-greasing of inner and outer bearings, lack of balancing weights, and the use of the interposition product.
It adds that the nose-gear manufacturer has highlighted the importance of adhering to instructions in aircraft and component maintenance manuals.
