Aircraft Accident/Incident Report

Shemya, Alaska 00000
Tuesady, April 6, 1993 2:30 AST

FLIGHT 583 WAS LEVEL AT 33,000 FEET WHEN THE LEADING EDGE SLATS DEPLOYED INADVERTENTLY. THE AUTOPILOT DISCONNECTED AND THE CAPTAIN WAS MANUALLY CONTROLLING THE AIRPLANE WHEN IT PROGRESSED THROUGH SEVERAL VIOLENT PITCH OSCILLATIONS AND LOST 5,000 FEET. THE SAFETY BOARD DETERMINED THAT THE INADVERTENT DEPLOYMENT OF THE SLATS WAS THE RESULT OD AN INADEQUATELY DESIGNED FLAP/SLAT HANDLE THAT ALLOWED THE HANDLED TO BE EASILY AND INADVERTENLY DISLODGED FROM THE UP/RET POSITION, THEREBY CAUSING SLAT EXTENSION.

THE NATIONAL TRANSPORTATION SAFETY BOARD DETERMINES THAT THE PROBABLE CAUSE OF THIS ACCIDENT WAS THE INADEQUATE DESIGN OF THE FLAP/SLAT ACTUATION HANDLE BY THE DOUGLAS AIRCRAFT COMPANY THAT ALLOWED THE HANDLE TO BE EASILY AND INADVERTENTLY DISLODGED FROM THE UP/RET POSITION, THEREBY CAUSING EXTENSION OF THE LEADING EDGE SLATS DURING CRUISE FLIGHT. THE CAPTAIN'S ATTEMPT TO RECOVER FROM THE SLAT EXTENSION, GIVEN THE REDUCED LONGITUDINAL STABILITY AND THE ASSOCIATED LIGHT CONTROL FORCE CHARACTERISTICS OF THE MD-11 IN CRUISE FLIGHT, LED TO SEVERAL VIOLENT PITCH OSCILLATIONS. CONTRIBUTING TO THE VIOLENCE OF THE PITCH OSCILLATIONS WAS THE LACK OF SPECIFIC MD-11 PILOT TRAINING IN RECOVERY FROM HIGH ALTITUDE UPSETS, AND THE INFLUENCE OF THE STALL WARNING SYSTEM ON THE CAPTAIN'S CONTROL RESPONSES. CONTRIBUTING TO THE SEVERITY OF THE INJURIES WAS THE LACK OF SEAT RESTRAINT USAGE BY THE OCCUPANTS.