What happened
On the date of the accident, an Atlantic Southeast Airlines, Inc. flight, operating as flight 4509, was performing a landing on runway 26R at Atlanta Hartsfield International Airport in Atlanta, Georgia. The flight crew reported that the approach to landing was uneventful. However, upon touchdown and following the deployment of the thrust reversers, the left main landing gear of the Bombardier CL6002B-19, registration N849AS, collapsed.
The investigation
The investigation focused on the structural integrity of the landing gear assembly. Examination revealed a fracture in the main fitting for the left main landing gear. This fracture was caused by a fatigue crack that originated from multiple points on the external surface of the wall at the shock strut radius run out area. Investigators found no evidence of material anomalies, such as corrosion or gouging, at the site where the fatigue crack began. Because the specific stresses that led to this fatigue cracking could not be clearly identified, the underlying root cause remained undetermined.
Following the event, Atlantic Southeast Airlines performed a fleet-wide inspection of all their Bombardier CL600-2B19 landing gear assemblies using visual and eddy current methods; no additional cracks were discovered. Regulatory bodies also took action: Transport Canada revised an existing Airworthiness Directive (AD) to prevent the escalation of inspection intervals, and the FAA issued a Notice of Proposed Rulemaking (NPRM). This proposal required repetitive detailed visual and eddy current inspections of the main landing gear main fittings, as well as specific servicing requirements for the shock struts, including checks for nitrogen pressure, chrome dimensions, and oil leakage.