What happened
On March 6, 2022, flight ENT515 and the crew of a Boeing 737-800, registration SP-ENM, departed from HEGN airport bound for HTZA. Approximately one hour into the flight, while cruising at altitude within the Egypt FIR (HECC), a cockpit alarm alerted the crew to a fire in the forward cargo compartment.
The crew immediately initiated emergency procedures as outlined in the Quick Reference Handbook (QRH) to address the potential fire. Following these protocols, the crew decided to return to the departure airport. During the approach and landing, the crew managed the aircraft's weight, noting that the aircraft mass exceeded the maximum landing weight, following procedures specified in the Flight Crew Training Manual (FCTM). The aircraft landed safely at the origin airport, and a subsequent inspection revealed no actual fire in the compartment.
The investigation
The PKBWL investigation examined the aircraft's systems and the environmental conditions present during the flight. The investigation focused on why the fire detection system was triggered despite the absence of an actual combustion event.
Findings
- The primary cause of the alarm activation was the malfunction of two fire detectors located in the A1 and B1 cargo compartments.
- Environmental factors contributed to the event, specifically the high humidity levels associated with operations in equatorial regions.
- The use of disinfectant products may have further increased the humidity levels within the cargo holds, potentially influencing the sensor behavior.
- This incident marked the second occurrence of similar detector malfunctions within a 12-month period.
Safety action
- The faulty detectors have been replaced.
- Implementation of monitoring procedures to track the frequency and trends of such malfunctions.