What happened
On 5 August 2005, an ATR 42-300, registration EI-BYO, was operating a public transport flight toward Cork Airport when the crew identified a performance discrepancy between the two engines. During the climb, the No. 1 engine began producing progressively less power, a condition that worsened as the aircraft reached higher altitudes. Despite the imbalance between the engines, the crew elected to continue the flight to Cork.
Upon landing, the crew feathered the No. 1 engine and shut it down shortly after touchdown. Once at the parking position, the cabin attendant alerted the crew to a fuel leak visible within the No. 1 engine nacelle. In response to the leak, the crew shut down the No. 2 engine and activated the fire handle for the No. 1 engine. The Airport Fire Service was summoned to the scene. Following a consultation with the Fire Chief, the 45 passengers were permitted to disembark via the aircraft stairs. There were no injuries and no damage to the aircraft.
The investigation
The investigation focused on the source of the fuel leak and the maintenance history of the engine components. Investigators traced the leak to a specific nut located on the fuel flow divider union. It was determined that this nut had backed off from the divider, allowing fuel to escape.
Review of the aircraft's maintenance records showed that while fuel nozzles had been replaced on the engine fuel pipe during a previous maintenance event, no work had been performed on that specific pipe since 5 June 2005. The investigation established that the nut had been incorrectly wire-locked during that prior maintenance task, which failed to secure the component against the vibrations inherent in engine operation.
Findings
- The primary cause of the power loss was a fuel leak originating from the No. 1 engine's fuel flow divider.
- The leak was caused by a nut on the fuel flow divider being incorrectly wire-locked, which allowed it to loosen due to engine vibration.
- The failure of the wire-locking mechanism led to a progressive reduction in fuel flow, resulting in the observed loss of engine torque and power.
Safety action
Following the incident, the operator implemented several corrective measures, including the issuance of an Engineering Notice to ensure technical personnel strictly adhere to the manufacturer's Maintenance Manual regarding the flow divider delivery tube nut. Additionally, a Quality Assurance Notice was issued requiring duplicate inspections whenever the fuel system downstream of the fuel booster pumps is disturbed. A fleet-wide inspection also identified one other instance of incorrect wire-locking. The engine manufacturer subsequently amended the relevant Cleaning Inspection and Repair Manual.