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Casualties unknown

Power Rollback on Four Engines During Thunderstorm Encounter (CFBAO)

Denver, CO, US

On May 1, 2000, a British Aerospace BAE 146-200 (registration CFBAO) operated by Air Bc, Ltd. was involved in an aviation accident near Denver, CO. Investigators recorded the probable cause as: In certain temperature and moisture conditions, the engines become susceptible to ice accumulation on the supercharger exit guide vanes. This reduces core engine airflow, resulting in a loss of power. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-06-10Data APIEditorial standards

While in IMC at FL 290, the number 1 engine power rolled back to flight idle. During descent to FL 260, two more engines also rolled back. Power returned below 12,500 feet; the flight landed safely.

Event Description

While operating in instrument meteorological conditions (IMC) at flight level 290 (FL 290), the power on the number 1 engine rolled back, dropping to flight idle. The operator reported considerable convective cloud and thunderstorm activity in the area, with cloud tops reaching FL 500.

As the flight descended to FL 260, the power on the number 2 and number 4 engines also rolled back. When the airplane passed 12,500 feet mean sea level (MSL), power returned to the three idling engines. The flight continued and landed without further incident.

Aircraft and Engine Details

The airplane was equipped with four unmodified Honeywell ALF502R engines. The source notes that in certain temperature and moisture conditions, these engines become susceptible to ice accumulation on the supercharger exit guide vanes. This ice accumulation reduces core engine airflow, resulting in a loss of power.

Regulatory Background

Early airworthiness directives (ADs) prohibited flight in icing conditions above 26,000 feet and at an outside air temperature above -40 degrees C, as well as within 30 nautical miles of thunderstorms. Some operators were granted waivers from these ADs. More recent airworthiness directives mandate certain engine modifications to be completed by December 2002. Newer models of the airplane feature redesigned engines.

Probable cause

In certain temperature and moisture conditions, the engines become susceptible to ice accumulation on the supercharger exit guide vanes. This reduces core engine airflow, resulting in a loss of power.
Icing

More accident analyses

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001212X20797. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.