NTSB Factual Report

On Monday, October 31, 1994, about 1600 CST, an Avions de Transport Regional ATR-72, N401AM, operated by Simmons Airlines as American Eagle flight 4184, struck the ground after the flightcrew lost control of the airplane during an adverse roll event at 9,200 feet. The captain, first officer, two flight attendants and 64 passengers received fatal injuries and the airplane was destroyed by impact forces. The instrument meteorological conditions (IMC) prevailed, both en-route and at the accident site; and an instrument flight rules flight plan had been filed. Flight 4184 was being operated under 14 CFR Part 121 at the time of the accident.

American Eagle flight 4184 was scheduled passenger service between Indianapolis, Indiana and Chicago, Illinois. The flight had proceeded uneventfully until it arrived in the Chicago area, where the flightcrew was instructed to "hold" for sequencing into Chicago's O'Hare Airport (ORD). Flight 4184 had been holding for approximately 32 minutes at 10,000 when the crew received a clearance to descend to 8,000 feet. During the descent to 8,000 feet and in a right turn in the holding pattern, the airplane rolled to approximately 70 degrees right wing down. The flightcrew attempted to recover, however, the airplane rolled to the right a second time and continued to roll to an inverted position.

NTSB Probable Cause

the loss of control, attributed to a sudden and unexpected aileron hinge moment reversal that occurred after a ridge of ice accreted beyond the deice boots while the airplane was in a holding pattern during which it intermittently encountered supercooled cloud and drizzle/rain drops, the size and water content of which exceeded those described in the icing certification envelope. The airplane was susceptible to this loss of control, and the crew was unable to recover. Contributing to the accident were: 1) the French Directorate General for Civil Aviation's (DGAC's) inadequate oversight of the ATR 42 and 72, and its failure to take the necessary corrective action to ensure continued airworthiness in icing conditions; and 2) the DGAC's failure to provide the FAA with timely airworthiness information developed from previous ATR incidents and accidents in icing conditions,3) the Federal Aviation Administration's (FAA's) failure to ensure that aircraft icing certification requirements, operational requirements for flight into icing conditions, and FAA published aircraft icing information adequately accounted for the hazards that can result from flight in freezing rain, 4) the FAA's inadequate oversight of the ATR 42 and 72 to ensure continued airworthiness in icing conditions; and 5) ATR's inadequate response to the continued occurrence of ATR 42 icing/roll upsets which, in conjunction with information learned about aileron control difficulties during the certification and development of the ATR 42 and 72, should have prompted additional research, and the creation of updated airplane flight manuals, flightcrew operating manuals and training programs related to operation of the ATR 42 and 72 in such icing conditions.