French investigators have determined that fatigue cracking in the undercarriage of an ACT Airlines Airbus A300B4 freighter caused the left main landing-gear to collapse after touchdown in Afghanistan.

The aircraft (TC-ACB) had been arriving at Bagram after a cargo service from Bahrain on 1 March 2010.

Its crew had already been alerted to a possible problem during the visual approach to runway 21 because cockpit indications showed the left main gear was not locked, and an absence of pressure in the green hydraulic system.

The A300 carried out two passes of the airport in order for air traffic controllers to observe the state of the undercarriage. It appeared normal but the pilots opted for a minimum-speed approach at 160kt.

About 18s after touchdown, during braking, the left gear collapsed, says French investigation authority BEA. The A300 departed the runway and came to rest 2,000m beyond the threshold. All five crew evacuated without injury.

BEA says the articulating arm, located at the top of the main gear leg, fractured as a result of fatigue cracking – adding that this fracture “probably” occurred as the gear retracted after take-off, when forces on the component were maximal.

The left gear subsequently deployed under gravity when the undercarriage was extended for landing, leading to a hydraulic leak.

BEA’s inquiry determined that some maintenance tasks on the gear, during its last overhaul at Turkish Technic, were “not completed in the prescribed manner”, but points out that the process layout of the maintenance manual could lead to “misunderstanding” or “omissions” when preparing job cards. Pitting and corrosion in the landing-gear assembly went undetected.

Turkish Technic and landing-gear manufacturer Messier-Bugatti-Dowty subsequently undertook a review of procedures, with Messier and Airbus emphasising the need to apply corrosion protection promptly to parts awaiting plating treatment.

Source: Cirium Dashboard