On March 31, 1993, the No. 2 engine and engine pylon separated from Japan Airlines, Inc. flight 46E, a Boeing 747-121, that had been wet-leased from Evergreen International Airlines, Inc., shortly after departure from Anchorage International Airport, Anchorage, Alaska. The accident occurred about 1234 Alaska standard time. The flight was a scheduled cargo flight from Anchorage to Chicago-O'Hare International Airport, Chicago, Illinois. On board the airplane were the flightcrew, consisting of the captain, the first officer, and the second officer, and two nonrevenue company employees. The airplane was substantially damaged during the separation of the engine. No one on board the airplane or on the ground was injured.
Flight 46E departed Anchorage about 1224 local time. The flight release/weather package provided to the pilots by Evergreen operations contained a forecast for severe turbulence and indicated that severe turbulence was reported by other large airplanes. As flight 46E taxied onto the runway to await its takeoff clearance, the local controller informed the flightcrew that the pilot of another Evergreen B-747 reported severe turbulence at 2,500 feet while climbing out from runway 6R.
After takeoff, at an altitude of about 2,000 feet, the airplane experienced an uncommanded left bank of approximately 50 degrees. While the desired air speed was 183 knots, the air speed fluctuated about 75 knots from a high of 245 knots to a low of 170 knots. Shortly thereafter, the flightcrew reported a "huge" yaw, the No. 2 throttle slammed to its aft stop, the No. 2 reverser indication showed thrust reverser deployment, and the No. 2 engine electrical bus failed. Several witnesses on the ground reported that the airplane experienced several severe pitch and roll oscillations before the engine separated.
Shortly after the engine separated from the airplane, the flightcrew declared an emergency, and the captain initiated a large radius turn to the left to return and land on runway 6R. The No. I engine was maintained at emergency/maximum power. While on the downwind portion of the landing pattern, bank angles momentarily exceeded 40 degrees, alternating with wings level. About 1245, flight 46E advised the tower that they were on the runway.
The National Transportation Safety Board determines that the probable cause of this accident was 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.
As a result of its investigation of this accident, the National Transportation Safety Board made seven recommendations to the Federal Aviation Administration, including the inspection of B-747 engine pylons, the potential meteorological hazards to aircraft,,, an increase in the lateral load capability of engine pylon structures, and the modification of the aircraft departure routes at Anchorage International Airport during periods of moderate or severe turbulence. The Safety Board recommended that the National Weather Service use the WSR-88D Doppler weather radar system at Anchorage, Alaska, to document mountain-generated wind fields in the Anchorage area and to develop detailed low altitude turbulence forecasts. Additionally, the Safety Board reiterated to the Federal Aviation Administration Safety Recommendation A-92-58, which urged the development of a meteorological aircraft hazard program to include other airports in or near mountainous terrain. Legend: