What happened
On August 8, 1998, an Embraer 145 (registration not provided) was prepared for an IFR flight from Hannover Airport to Manchester. The aircraft was carrying 33 passengers and 5 crew members. Following a previous landing, the pilot had started the Auxiliary Power Unit (APU) to provide electrical power and bleed air for the air conditioning systems.
During the boarding process, a cabin crew member reported a smell of fuel vapors. The pilot checked the status of the fuel pumps, APUS, and air conditioning, but noted nothing unusual. As the start sequence for the right engine began, a loud bang was heard and felt when the engine reached approximately 13% N2. Although engine instruments and the EICAS showed normal parameters, the crew soon noticed heavy fuel odors entering the cabin. The captain ordered an immediate evacuation and shut off the fuel supply valves. Shortly after, black smoke was observed emanating from the rear of the aircraft, and the crew activated the engine fire extinguishing systems.
Ground personnel and airport firefighters managed to extinguish the fire using handheld extinguishers before the arrival of larger fire apparatus. There were no injuries and no damage to the aircraft, aside from fuel contamination in the right engine from the extinguishing agent.
The investigation
BFU investigators found that the interior of the right engine was flooded with fuel, which was leaking from the nozzles into the engine casing. Upon inspection of the Fuel Metering and Pump Unit (FMPU), investigators discovered that fuel flowed heavily from the unit to the nozzles when the electric pumps were activated, even though the engine was not running.
Subsequent testing of the FMPU at the manufacturer's facility revealed that the Air Vent Solenoid Valve (AVSV) failed to close properly in its de-energized state. This allowed fuel to reach the outlet despite the Air Vent Valve (AVV) being closed. Further disassembly of the valve revealed that a metal chip, left over from the manufacturing process, had become lodged between the valve insert and the housing. This chip caused a groove in the housing and made the valve insert difficult to screw in, likely requiring excessive force during assembly.
Findings
- The engine fire was caused by the failure of the Air Vent Solenoid Valve to close completely, which allowed fuel to flood the engine core.
- The fuel pressure required for this leakage was provided by the electric fuel pump, which was active to support the APU.
- The fire was ignited when the engine's ignition system activated during the automatic start sequence at 13% N2.
- The presence of a manufacturing defect (a metal chip) prevented the valve from sealing properly.
- The initial smell of fuel vapors was not treated as a critical warning by the crew, as such odors are common on airport aprons.