The airplane was in a holding pattern and was descending to a newly assigned
altitude of 8,000 feet when it experienced an uncommanded roll excursion and
crashed during a rapid descent. The loss of ccontrol was attributed to a sudden
and unexpected aileron hinge moment reversal that occurred after a ridge of ice
accreted beyond the deice boots. The manufacturer failed to disseminate adequate
warnings and guidance to operators about the adverse characteristics of, and
techniques to recover from, ice-induced aileron hinge moment reversal events;
and failed to develop additional airplane modifications, which led directly to
this accident. The DGAC failed to require the manufacturer to take additional
corrective actions, such as performing additional icing tests, issuing more
specific warnings regarding the aileron hinge moment reversal phenomenon,
developing additional airplane modifications, and providing specific guidance on
the recovery from a hinge moment reversal, which led directly to this accident.
The ability of the FAA to to monitor, on a real-time basis, the continued
airworthiness of the ATR airplanes was hampered by the inadequately defined
lines of communication, the inadequate means for the FAA to retrieve pertinent
information, and the DGAC's failure to provide the FAA with critical
airworthiness information., because of the DGAC's apparent belief that the
information was not required to be provided under the terms of the Bilateral
Airworthiness Agreement.
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
because: 1) ATR failed to completely disclose to operators, and incorporate in
the ATR 72 airplane flight manual, flightcrew operating manual and flightcrew
training programs, adequate information concerning previously known effects of
freezing precipitation on the stability and control characteristics, autopilot
and related operational procedures when the ATR 72 was operated in such
conditions; 2) 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 3)
the DGAC's failure to provide the FAA with timely airworthiness information
developed from previous ATR incidents and accidents in icing conditions, as
specified under the Bilateral Airworthiness Agreement and Annex 8 of the
International Civil Aviation Organization. Contributing to the accident were: 1)
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 and other icing
conditions not specified in 14 Code of Federal Regulations (CFR) Part 25,
Appendix C; and 2) the FAA's inadequate oversight of the ATR 42 and 72 to ensure
continued airworthiness in icing conditions. (NTSB Report AAR-96/01)