What happened
During cruise flight at 12,000 feet mean sea level, the crew of the aircraft received a fire indication from the number two engine. In response to the alert, the crew shut down the engine while still in flight. The aircraft subsequently landed uneventfully.
The investigation
The investigation focused on the number two engine and identified a cracked left fuel manifold segment. A metallurgical analysis of the component revealed that the crack was characterized by fatigue striations. The failure occurred at a specific location on the manifold where there was an abrupt change in material thickness.
It was noted that the operator had reported two previous occurrences of cracked manifolds, which had been investigated by the NTSB. Before this specific incident, the manufacturer had implemented three measures to address fuel manifold cracking: introducing a redesign of the manifold segments, agreeing to replace all operator manifold assemblies with the improved design, and implementing an eddy current inspection procedure for crack detection.
Findings
Following the investigation of this incident, the FAA mandated more frequent inspection intervals and required the adoption of the new eddy-current inspection process for any manifolds that had not yet been upgraded to the improved design.