What happened
On June 4, 2021, at approximately 01:23 LMT, a crew consisting of a pilot, a medical rescuer, and a physician departed from Sandomierz for an air medical transport mission to Kraków. The aircraft, an Eurocopter EC-135 P3 with registration SP-HXR, was operating as part of the Kraków Air Ambulance service.
During the 21st minute of the flight, a "FIRE EXT" warning appeared on the Caution and Advisory Display (CAD) regarding engine number 1. In response to this alert, the pilot shut down engine number 1. Following the shutdown, the crew returned to their base at Kraków-Balice Airport, where they landed safely. During the flight, the aircraft experienced brief periods where engine parameters exceeded permissible limits; however, the engine manufacturer, Pratt & Whitney Canada, later determined these excursions remained within the operational limits of the engine.
The investigation
The PKBWL examined the sequence of events and the cockpit actions taken by the crew. The investigation focused on the origin of the fire warning and the pilot's decision-making process following the alert on the CAD. Technical inspections were conducted at the Kraków Maintenance Station (SOT) in consultation with the aircraft manufacturer to verify the operational status of the engine and the fire suppression system.
Findings
The investigation established that the primary cause of the event was the accidental switching of the FIRE E/W switch to the TEST position. This action led to the pilot's incorrect interpretation of the resulting warning on the CAD, which subsequently prompted the unnecessary shutdown of a functional engine.