Engine Fire Warning During Climb Leads to Cowling Separation (N619US)

Incident Details

During the climb phase of flight, the crew heard a loud bang and felt the aircraft shudder. Immediately afterward, the oil pressure and oil quantity indicators for the number three engine showed low readings. The fire warning light illuminated and the associated warning bell sounded. In response, the crew shut down the affected engine and continued to a landing without any further issues.

Postflight Inspection

After landing, a postflight inspection revealed that the outboard cowling of the number three engine had separated from the aircraft. The cowling was later located in a suburban area ten miles southwest of the departure airport.

Engine Teardown Findings

A teardown of the number three engine was conducted to determine the cause of the event. The investigation found a crack in a vent line strut located in the diffuser area. This crack allowed bleed air to escape and ignite oil in the area of the number three bearing. The resulting fire created pressure that forced the flames through the compartment breather air tube. This pressure disintegrated the main bearing breather tube elbow. The force of the explosion at the disintegrating elbow then blew the outboard cowling off the engine.