NTSB Probable Cause

THE FAILURE OF THE FLIGHTCREW TO DETECT AND REMOVE ICE CONTAMINATION ON THE AIRPLANE'S WINGS, WHICH WAS LARGELY A RESULT OF A LACK OF APPROPRIATE RESPONSE BY THE FEDERAL AVIATION ADMINISTRATION, DOUGLAS AIRCRAFT COMPANY, AND RYAN INTERNATIONAL AIRLINES TO THE KNOWN CRITICAL EFFECT THAT A MINUTE AMOUNT OF CONTAMINATION HAS ON THE STALL CHARACTERISTICS OF THE DC-9 SERIES 10 AIRPLANE. THE ICE CONTAMINATION LED TO WING STALL AND LOSS OF CONTROL DURING THE ATTEMPTED TAKEOFF. (NTSB REPORT AAR-91/09)