NTSB Identification: CHI96IA173.
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Scheduled 14 CFR operation of AIR WISCONSIN (D.B.A. UNITED EXPRESS )
Incident occurred Sunday, May 26, 1996 in DES MOINES, IA
Probable Cause Approval Date: 02/28/1997
Aircraft: British Aerospace BAE 146, registration: N608AW
Injuries: 58 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

While operating in clouds at flight level 290, in an area with thunderstorms and turbulence, the airplane experienced a loss of power in all four engines. Information from the flight data recorder indicated that during descent from flight level 290, an elevator oscillation occurred. The #1 and #2 engines were shut down due to high turbine gas temperatures. The #2 engine was restarted before making an emergency landing at the Des Moines Airport. The captain reported that the airplane had been flown into severe icing conditions. The aircraft flight manual (AFM) prohibited flight in icing conditions above 26,000 feet (except when necessary for descent). Also, the AFM stipulated the minimum engine speeds which needed to be maintained while operating in icing conditions; it also required that the thrust management system (TMS) be disconnected in icing conditions. There were indications that the TMS was disconnected about 230 seconds after engine roll-back began. Additionally, the AFM did not provide accurate information concerning 'in cloud' correction factor for the outside temperature thermometer.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

failure of the flight crew to follow proper procedures, which resulted in an accumulation of ice and subsequent loss of engine power. Factors relating to the incident were: thunderstorms, turbulence, icing conditions, and the inaccurate method that was provided by the manufacturer for determining 'in cloud' air temperature and icing conditions.

Full narrative available

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