What happened
On 27 November 2015, an Airbus A319-112, registration D-AIBC, was preparing for a scheduled passenger flight from Dublin to Munich. During the pushback process from parking stand 306L, the flight crew attempted to start the engines. The No. 2 engine failed to ignite due to insufficient bleed air pressure from the Auxiliary Power Unit (APU).
Following the failed start, the aircraft was towed back to its parking stand. Shortly after the aircraft came to a halt, the cabin crew notified the flight deck of smoke visible within the cabin. In response, the commander declared a ‘Mayday’ and prepared the cabin for an emergency evacuation. During the initial response, the cabin crew had already moved the emergency door slides from the armed to the manual position.
As the smoke began to dissipate, the commander opted to disembark the 104 passengers and 5 crew members via the airbridge rather than utilizing the emergency slides. There were 0 injuries reported during the event.
The investigation
Investigators examined the aircraft's APU and the surrounding systems to identify the source of the smoke. While the cockpit initially showed no fire indications, the commander had discharged a fire extinguisher into the APU compartment as a precaution.
During subsequent maintenance testing, the crew restarted the APU in the presence of the Airport Fire Service. This test resulted in the cabin filling with smoke once again. Inspection of the aircraft revealed oil visible on the exterior of the APU compartment door and the rear fuselage. Further disassembly of the APU at an overhaul facility revealed that oil had contaminated the intake plenum, various ducts, and the low oil pressure tube.
Findings
- The primary cause of the smoke entering the cabin was an oil leak from the area of the oil cooler.
- It is probable that the leaking oil was drawn into the airflow by the load compressor, subsequently entering the air conditioning system.
- The initial failure of the No. 2 engine to start was caused by a lack of sufficient bleed air pressure.
- This lack of pressure was likely due to a malfunctioning inlet air temperature and pressure sensor, which had been contaminated by the same oil leak affecting the plenum.