Incident
On 26 November 2005 at 10:20 p.m., an Airbus A320-231 with registration VT-ESF was departing from Singapore Changi Airport to Chennai. While taxiing on Taxiway EP, the left hand main landing gear (MLG) bogie beam fractured. The aircraft came to a stop on the taxiway between Taxiways B2 and B3. There were no injuries.
Aircraft Details
The aircraft was an Airbus A320-231, serial number MSN 432, equipped with two V2500-A1 engines. The flight was a scheduled passenger service. The left hand MLG had part number 201174079-010 and serial number DLG-0015. The bogie beam and dressings had part number 201216015 and serial number B34. The MLG had accumulated 21,170 cycles since new and 4,438 cycles since its last overhaul.
Damage
The left hand MLG bogie beam fractured into two parts at the pivot pin attachment hole. The left MLG oleo strut attachment lugs suffered scuffing from being dragged on the ground for about 50 metres. The lugs were found dug into the asphalt due to the weight of the aircraft. The taxiway surface sustained gouges over a distance of about 50 metres, with depths between 1 and 2 cm.
Investigation Findings
Examination of the fractured bogie beam revealed corrosion pits underneath the cadmium plating at the radius intersection of the bogie pivot pin bore and the cross bolt hole. At two locations, fatigue cracks initiated and propagated from these corrosion pits. Stress corrosion cracking ultimately led to the fracture.
The overhaul carried out in July 2003 for the bogie beam did not achieve the required cadmium plating minimum thickness at the cross bolt hole. However, the cadmium thickness was not a factor in the corrosion development or crack initiation. The visual inspections performed during the overhaul were unlikely to detect corrosion pitting underneath the protective coating and plating. The grease around the grease nipples on the left hand MLG bogie was found dried up and black, and analysis showed a high chromium level in the grease from the inboard pivot pin bushing, indicating considerable wear.
Conclusion
The cause of the bogie beam fracture was the corrosion pits that developed at the radius intersection of the bogie beam pivot pin bore and cross bolt hole. Fatigue cracks initiated and propagated from these corrosion pits, and stress corrosion cracking led to the fracture.