Incident Overview
On August 22, 2020, a Boeing 737-800 (registration SP-ENL) experienced a fuel system alert while taxiing for departure at Warsaw Chopin Airport (EPWA). The crew received a MASTER CAUTION FUEL warning and a FUEL FILTER BYPASS alert for engine number 1. In response, the aircraft was stopped on the taxiway, and the crew requested permission from air traffic control to return to the apron.
Crew Actions
While awaiting clearance, the crew consulted the Non-Normal Checklist (NNC) for a fuel filter bypass. However, the checklist procedures were found to be inapplicable as they addressed only in-flight events, not ground operations. The FUEL FILTER BYPASS alert extinguished itself after a few seconds but reactivated approximately 33 seconds later. Meanwhile, air traffic control authorized the aircraft to taxi back to the apron. During the taxi, the alert turned off again without crew intervention. Upon reaching the apron, the aircraft was handed over to the operator's maintenance personnel.
Investigation Findings
The investigation, conducted under the supervision of the State Commission on Aircraft Accident Investigation (PKBWL), was unable to determine the root cause of the fuel filter contamination that triggered the alerts. The commission noted that the fuel filter bypass indication and the MASTER CAUTION FUEL signal were generated by an unspecified contamination event, but the precise source could not be identified. No contributing circumstances were established.
Safety Actions
Two safety actions were proposed by the investigating entity. The operator's Quality Department was instructed to monitor fuel supply subcontractors, emphasizing compliance with recommendations in Service Information Bulletin (SIB) 2018-10. The Safety Department was tasked with publishing the final report in the next edition of the operator's Flight Safety Bulletin. No additional safety recommendations were formulated by the commission.