On August 20, 1983, a Boeing 767 (registration N609UA) was involved in an aviation accident near Denver, CO. Investigators recorded the probable cause as: The inability of the engines to accelerate after the manually induced surge was due to contaminated fuel nozzles which significantly reduced combustion chamber efficiencies and which resulted in a subidle stall. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 5 related events involving the same aircraft type or operator are linked below.
An aircraft experienced dual engine surges and exceedance of maximum exhaust gas temperature during descent. Both engines were shut down and later restarted. Investigation found contaminated fuel nozzles caused a subidle stall.
Event Description
The aircraft was descending from flight level 410 with its throttles set to idle. Upon adding power at flight level 295, the left engine surged and its exhaust gas temperature exceeded the maximum limit. Eighteen seconds later, the right engine also surged and exceeded its maximum exhaust gas temperature. The left engine was shut down at flight level 200, and the right engine was shut down at flight level 177. Both engines were successfully restarted at approximately flight level 150.
Investigation Findings
The investigation determined that the inability of the engines to accelerate after the manually induced surge was due to contaminated fuel nozzles. The contamination significantly reduced combustion chamber efficiencies, which resulted in a subidle stall. This condition prevented the engines from accelerating normally.
Probable cause
The inability of the engines to accelerate after the manually induced surge was due to contaminated fuel nozzles which significantly reduced combustion chamber efficiencies and which resulted in a subidle stall.
