National Transportation Safety Board
Office of Public Affairs
(Washington, DC) -- In one of its most comprehensive accident reports, the National Transportation Safety Board (NTSB) has determined that a series of failures by French and American aviation authorities and the maker of ATR-42 and ATR-72 aircraft led to the fatal crash of American Eagle Flight 4184 in 1994.
A twin turbo-prop ATR-72 nose-dived into a soybean field near Roselawn, Indiana, on Oct. 31, 1994, killing everyone on board: four crewmembers and 64 passengers.
The Safety Board attributed the aircraft's loss of control to a sudden and unexpected movement of an aileron -- a flight control on the wing -- that occurred after a ridge of ice formed behind the plane's deice boots -- mechanisms that shed in-flight ice buildup from the wings.
The NTSB said the probable cause of the control loss resulted from the failure of Avions de Transport Regional (ATR), the plane manufacturer, to completely disclose adequate information about previously known effects of freezing precipitation on the plane's stability and control characteristics, autopilot and operational procedures. This vital safety information, the Safety Board said, was not included in the ATR flight manual, flightcrew operating manual and flightcrew training programs.
The NTSB also pointed to inadequate oversight of ATR-42 and ATR-72 aircraft by the French aviation regulatory agency, the Directorate General for Civil Aviation, and its failure to take necessary corrective action to ensure continued airworthiness of the aircraft in icing conditions.
In its accident report, the Board said that French regulatory authorities failed to provide the Federal Aviation Administration (FAA) with timely airworthiness information developed from previous ATR incidents and accidents in icing conditions -- a breach of international aviation agreements.
Contributing to the Roselawn accident, the Safety Board determined, was FAA's failure to adequately oversee the continued airworthiness of ATR-42 and ATR-72 aircraft. Another contributing factor was FAA's failure to update aircraft certification requirements to reflect more hazardous freezing rain conditions. Current icing certification requirements are based on meteorological and technical research dating back to the 1940s and 1950s.
The NTSB also issued a series of 26 safety recommendations, mostly to the FAA, to vastly improve weather information and how it is transmitted among aircraft dispatchers, flightcews and air traffic controllers.
The Safety Board urged the FAA to make sweeping changes and expand its aircraft icing certification criteria and testing. These changes must be based on up-to-date weather research and require safe performance of aircraft in freezing drizzle, freezing rain, and mixed water and ice crystal conditions, the Board said.
If an aircraft maker cannot demonstrate safe operation in tougher icing certification requirements, operational limits must be imposed on the aircraft to prohibit flightcrews from flying in those conditions. Flightcrews must also be given the means to positively determine when icing conditions exceed an aircraft's certification limits, the Board said.
Another important recommendation, issued by the NTSB, would require aircraft manufacturers to provide information to the FAA and aircraft operators about undesirable flight characteristics that go beyond the protected flight regime.
The NTSB also urged the FAA to revamp the way its aircraft evaluation group does business, review and revise the way its monitors and verifies certification of aircraft by foreign countries, and require operators of transport aircraft to provide flightcrew training that addresses recovery from unusual aircraft events including extreme flight attitudes.
Additional NTSB recommendations urged AMR Eagle to require dispatchers to inform flightcrews of pertinent enroute weather information so flightcrews can use the information in their pre-fight and inflight decisions; encourage captains to observe the "sterile cockpit" environment when an airplane is holding, regardless of altitude, in icing conditions that have the potential to demand significant flightcrew attention; and to eliminate conflicts in flightcrew guidance in aircraft flight manuals, flight operations manuals and other published material.
The Safety Board also urged the National Oceanic and Atmospheric Administration (NOAA) to develop methods to define specific locations of atmospheric conditions -- including freezing drizzle and freezing rain -- and produce short range forecasts for specific geographic areas that are valid for two hours or less.
The NTSB's complete report, PB96-910401, may be purchased from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161. The telephone number is (703) 487-4650.
Media contact: NTSB Office of Public Affairs
The National Transportation Safety Board (NTSB) is an independent federal agency charged with determining the probable cause
of transportation accidents, promoting transportation safety, and assisting victims of transportation accidents and their families.