UK Air Accidents Investigation Branch (AAIB) says the likely origin of the main landing gear (MLG) failure of the Boeing 737-400 Freighter at East Midlands Airport in 2014, was an area of intense localised heating.
The branch released a report on Thursday 8 April into the Air Contractors aircraft incident, which caused the closure of the airport on 29 April after the failure at 01.28h. The incident led to 16 cargo flights being diverted to London Stansted Airport or cancelled that day.
The freighter departed Paris Charles de Gaulle Airport for East Midlands at 00.40h, loaded with 10 tonnes of cargo. Once landed at East Midlands, when it was slowing down to exit the runway, part of the MLG failed. Damage was caused to the left main landing gear, left portion of the wing and engine (see AAIB picture).
The AAIB says in the report: “The failure was a result of stress corrosion cracking and fatigue weakening the high strength steel substrate, about 75 millimetres above the MLG axle.”
It adds it is likely heat damage was sustained by the inner cylinder during the overhaul process, as indicated by, “chicken wire cracking within the chrome plating over the majority of its surface”.
However, the AAIB says this was not severe enough to have damaged the steel substrate and may have been, “coincidental”. The AAIB adds the risk of heat damage occurring during complex landing gear plating and refinishing processes is, “well understood,” and mitigated by manufacturers and overhaul agencies, so damage during the refinishing process cannot be discounted.
Despite the scepticism about the heating’s role, the AAIB concludes: “The origin of the failure was an area of intense, but very localised heating, which damaged the chrome protection and changed the metallurgy.” This, it adds, resulted in a surface corrosion pit, which led to stress corrosion cracking, fatigue propagation and failure of the inner cylinder under normal loading. The AAIB says the aircraft landed normally and there were no adverse weather conditions. There was two crew onboard and no injuries.