Incident Overview
Shortly after takeoff from Anchorage, the airplane flew into an area of severe turbulence while climbing through an altitude of about 2000 feet. During the encounter, the number 2 engine and its pylon separated from the airplane. The flightcrew declared an emergency and returned to Anchorage, where an uneventful landing was accomplished.
Investigation Findings
The investigation revealed that a strong easterly wind interacted with mountains east of Anchorage, producing mountain wave activity. This resulted in the aircraft encountering severe or possibly extreme turbulence. There was evidence that this turbulence produced dynamic multi-axis lateral loadings that exceeded the ultimate lateral load-carrying capability of the number 2 engine pylon. The pylon's load-carrying capability had already been reduced by the presence of a fatigue crack near the forward end of the pylon's forward firewall web.