NTSB Identification: ENG08IA001
Scheduled 14 CFR Part 121: Air Carrier operation of US AIRWAYS INC (D.B.A. US Airways)
Incident occurred Sunday, October 28, 2007 in Charlotte (CLT), NC
Probable Cause Approval Date: 04/12/2011
Aircraft: BOEING 757-225, registration: N919UW
Injuries: Unavailable

NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft incident report.

On October 28, 2007, a US Airways Boeing 757-200, N919UW, experienced a fracture of the truck beam on the left hand (LH) main landing gear (MLG) while preparing for departure from Charlotte/Douglas International Airport (CLT). The airplane was loaded with flight crew, cabin crew, passengers and cargo at the time of the truck beam failure. There was no other damage to the airplane and there were no injuries to any of the occupants or the ground personnel. The truck beam had accumulated 24,025 cycles since new and 2,707 cycles since its last overhaul which occurred in May, 2005.

The truck beam fracture initiated by fatigue and stress corrosion cracking from pits that were present on the ID surface of the truck beam, under the protective finishes. Crack propagation occurred by alternating modes of stress corrosion cracking and fatigue until final fracture occurred by ultimate ductile separation. The condition of the surface finishes and base metal at the fracture initiation area indicated that the pitting was present before the last application of cadmium plating and primer, rather than the result of corrosion since the last overhaul. The observed pitting appeared to be remnants of incomplete corrosion removal during the last overhaul. Residual stress analysis of the ID surface in the fracture initiation region suggested that the blended area did not receive adequate peening to restore typical residual compressive stresses. The observed reduction in residual compressive stresses likely contributed to the fracture initiation. The wall thickness at the area of fracture initiation measured 0.29” and was within drawing dimensional tolerances. Chemical analysis and hardness testing verified that the truck beam was fabricated from the required material in the specified heat treated condition. Evaluation of the protective finishes on the truck beam indicated that the cadmium plating on the ID surface did not meet the minimum thickness requirements.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The truck beam fracture initiated by fatigue and stress corrosion cracking from pits that were present on the ID surface of the truck beam, under the protective finishes. Crack propagation occurred by alternating modes of stress corrosion cracking and fatigue until final fracture occurred by ultimate ductile separation. The condition of the surface finishes and base metal at the fracture initiation area indicated that the pitting was present before the last application of cadmium plating and primer, rather than the result of corrosion since the last overhaul. The observed pitting appeared to be remnants of incomplete corrosion removal during the last overhaul.

Full narrative available

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