Accident Sequence
During takeoff for a retardant drop mission, shortly after the landing gear was retracted, a ball of fire was observed emanating from the left jet engine. The airplane then rolled steeply to the left and descended into the terrain.
Before takeoff, the captain stated he would make the takeoff and provided a briefing regarding the runway and emergency intentions. However, shortly thereafter, the captain informed the co-pilot that the co-pilot would perform the takeoff. On the cockpit voice recorder, the co-pilot responded, "Same briefing (sound of laughter)." No additional takeoff briefing was given by the co-pilot, and the captain did not request one.
During the initial climb, the captain stated he detected a fire on the left side of the airplane. The co-pilot responded that he was holding full right aileron. At no point did either pilot call for jettisoning the retardant load as required by company standard operating procedures, nor did they verbally enunciate the jet engine fire emergency checklist. Recorded data showed that airspeed decayed below the minimum control speed (Vmca), resulting in an increased roll rate to the left and impact with terrain.
Findings
Metallurgical examination revealed that the 11th stage compressor disc of the left jet engine failed in fatigue, causing catastrophic failure of the compressor section and initiating the engine fire. The fracture originated at several points from scratches in the surface finish of the disc. These scratches were too small to be detected by the approved inspection procedures used by the company. A review of the FAA-sanctioned Approved Aircraft Inspection Program found no shortcomings or anomalies in its performance or documentation. Post-accident examination of the airframe and the three remaining engines revealed no anomalies that would have precluded normal operations.
Probable Cause and Contributing Factors
The official probable cause was the failure of the flight crew to maintain airspeed above in-flight minimum control speed (Vmca) after losing power in the left jet engine during initial climb after takeoff. Contributing factors were the crew's inadequate cockpit resource management procedures, the captain's failure to assume command during the emergency, the flight crew's failure to execute the jet engine fire emergency procedure, and the failure to jettison the retardant load.