What happened
On August 15, 2011, a Bombardier CRJ700 (registration F-GRZH) operated by Brit Air departed Lyon Saint Exupéry Airport for Barcelona, Spain, carrying 36 people. During the initial climb, while passing 2,800 ft, the crew heard two distinct noises. Although engine parameters initially appeared normal, the left engine fire alarm triggered once the aircraft reached 4,000 ft.
The crew immediately implemented engine fire procedures, which resulted in the shutdown of the left engine and the discharge of both fire extinguishing agents. After transmitting a distress message to air traffic control, the crew performed a turnaround and landed the aircraft on runway 31R. All 32 passengers and the crew evacuated the aircraft without injury, though the left engine sustained damage.
The investigation
The investigation focused on the left General Electric CF34-8C5B1 engine. External inspection revealed a burned area, and upon opening the cowlings, investigators located the fire's origin at the Operability Bleed Valve (OBV).
Detailed analysis showed that a fuel supply line fitting for the OBV had disconnected from its housing, causing pressurized fuel to leak. The investigation determined that the fitting had loosened, creating play that eventually wore down the threads in the aluminum housing of the OBV. This degradation caused the fitting to eventually detach.
Maintenance records showed the engine had completed 15,413 flight hours and 14,343 cycles. The OBV was an original component, and the manufacturer did not require specific maintenance for this part beyond general visual inspections. No specific maintenance had been performed on this system during the engine's two previous shop visits.
Findings
- The fuel leak was caused by the disconnection of a fuel supply line fitting at the OBV.
- Mechanical forces acting on the fuel line caused the fitting to loosen, leading to thread wear in the aluminum housing.
- The lack of a scheduled maintenance or inspection program for the OBV meant the developing degradation could not be detected before the failure occurred.
- This incident was not isolated, as two similar occurrences had been recorded on other CRJ aircraft using the same engine type.