What happened
On 28 May 2021, an Airbus A320-232, registration 9H-LOZ, was conducting a routine preservation flight from London Stansted Airport. During the final approach to Runway 22, the aircraft's No 2 engine experienced a sudden loss of power. At an altitude of approximately 950 feet, an 'eng 2 fadec fault' alert appeared on the cockpit displays.
The flight crew responded by executing a missed approach. During the subsequent holding pattern, the crew noted that the engine would not respond to throttle movements and that engine parameters appeared to be frozen. Following established checklists, the crew started the Auxiliary Power Unit and shut down the affected engine. The aircraft declared a MAYDAY and returned to Stansted, completing a safe single-engine landing with no injuries to the two crew members.
The investigation
Investigators examined the aircraft's post-flight reports and Digital Flight Data Recorder. The analysis revealed several additional fault messages, including issues related to the engine dedicated alternator and the propulsion system. While an insulation failure was found in the engine dedicated alternator, investigators ruled it out as the primary cause because no corresponding N2 speed fluctuations were recorded.
Further inspection of the Fuel Metering Unit (FMU) revealed internal fuel leaks around the mechanical control valves. Data analysis confirmed that the engine's Engine Pressure Ratio (EPR) decreased significantly while the engine was still functioning, which was inconsistent with a standard overspeed event.
Findings
- The reduction in engine power was caused by the uncommanded activation of the overspeed protection valve within the FMU.
- This activation restricted fuel flow to a fixed level just below flight idle, rendering the engine unresponsive to pilot throttle inputs.
- The engine parameters appeared frozen because the valve was hydraulically latched and could only be reset by an engine shutdown.
- Previous similar incidents involving V2500 engines have been documented, involving similar uncommanded valve closures.
Safety action
- The engine manufacturer is implementing product improvement changes to the FMU, targeted for release in late 2022.
- The aircraft manufacturer agreed to review the Flight Crew Operating Manual (FCOM) to clarify that engine parameters may appear frozen or abnormal rather than displaying 'XX' during a FADEC fault.