McDonnell Douglas MD-11FEDERAL EXPRESS CORP

The MD-11 airplane experienced structural damage to the left elevator during an abrupt maneuver while descending to land. The abrupt maneuver was initiated by the flight crew in response to a false ground proximity warning system (GPWS) alert that occurred as the airplane was encountering heavy precipitation at an altitude of about 9,800 feet above mean sea level. The GPWS warning subsided during the maneuver. The airplane landed uneventfully. Both flight crewmembers, the sole occupants, were not injured. Post-flight inspection of the airplane revealed that the outboard portion of the left elevator, including the balance weight, was partially separated. The flight crew stated that they had no problems with aircraft handling after the escape maneuver. The investigation revealed that the escape maneuver was aggressive and consistent with procedures that are published in Federal Express' airplane flight manual for "GPWS Pull Up Warning." The elevator damage occurred as a result of an excedence of the airplane's design aerodynamic stall buffet boundary, which led to a severe vibration of the elevator. The stall buffet boundary was exceeded as a result of the captain's initiation of the escape maneuver. The false reading of the no. 1 and no. 2 radio altimeters prompted the false GPWS warning and was most likely due to their signal return off of heavy precipitation. No post-accident mechanical deficiencies were found with the flight controls, avionics, or elevator structure.