Atlantic Southeast Airlines Flight 4509

A Bombardier CL6002B-19, N849AS, operated by Atlantic Southeast Airlines, Inc., as flight 4509, experienced a left main landing gear failure during landing on runway 26R, at the Atlanta Hartsfield International Airport, in Atlanta, Georgia. According to the flight crew, and confirmed by the FDR, the approach to landing was uneventful. Upon landing the pilot deployed the thrust reversers and the left main landing gear collapsed. Fracture of the main fitting for the left main landing gear was caused by a fatigue crack that emanated from multiple origins at the external surface of the wall at the shock strut radius run out area. No evidence of material anomalies, such as corrosion or gouge damage, was found at the fatigue origin area. Because the stresses leading to the fatigue crack of the main fitting have not clearly been identified, the root cause of the fatigue cracking has not been determined. During the investigation, Atlantic Southeast Airlines did a Fleet Wide inspection of all their Bombardier Inc., Model CL600-2B19 aircraft landing gear assemblies, which included visual and eddy current inspections. Their inspections found no additional cracked landing gear. Additionally, Transport Canada issued a revised AD, which eliminated the escalation of the eddy current inspection intervals as allowed in their previous AD. Also, the FAA issued an NPRM in response to Transport Canada AD, which requires repetitive detailed visual and eddy current inspection of the main landing gear main fitting. The NPRM if adopted would produce another AD that is applicable to certain Bombardier Model CL600-2B19 (Regional Jet Series 100 & 440) airplanes. The proposal would require repetitive detailed and eddy current inspections on the main fittings of the main landing gears (MLG) to detect discrepancies, and related investigative/corrective actions if necessary. The proposal also requires servicing of the shock strut of the MLGs; inspection the shock strut of the MLGs for nitrogen pressure, visible chrome dimension, and oil leakage; and servicing any discrepant strut. Transport Canada has also accepted Messier-Dowty’s redesign of the main fitting, on condition that the testing of the new design would be completed successfully. The testing is scheduled to commence in July 2004. Once the testing is completed Transport Canada will mandate the installation of the new design of the main fitting as the terminating action for the AD's.

Verbatim NTSB analysis and probable cause from the NTSB dataset