Primary finding
Probable cause
The lateral separation of the no. 2 engine pylon due to an encounter with severe or possibly extreme turbulence that resulted in dynamic multi-axis lateral loadings that exceeded the ultimate lateral load-carrying capability of the pylon, which was already reduced by the presence of the fatigue crack near the forward end of the pylon's forward firewall web.
Investigator assessment
Analysis narrative
Shortly after takeoff from anchorage, the airplane flew into an area of severe turbulence, while climbing through an altitude of about 2000 feet. The number 2 engine and engine pylon separated from the airplane. The flightcrew declared an emergency and the flight return to anchorage, where an uneventful landing was accomplished. The investigation revealed that a strong easterly wind interacted with mountains east of anchorage, which produced mountain wave activity. The aircraft encountered severe or possibly extreme turbulence. There was evidence that this resulted in dynamic multi-axis lateral loadings that exceeded the ultimate lateral load-carrying capability of the number 2 engine pylon, which had already been reduced by the presence of a fatigue crack near the forward end of the pylon's forward firewall web.
Source record
Factual narrative
See NTSB blue cover aviation accident report aar-93-06 for further information. -