What happened
On June 16, 2017, an Airbus A319-114 was performing a non-precision approach to runway 33 at Hamburg Airport. During the approach, at an altitude of approximately 6,000 feet, the flight crew detected an unpleasant, chemical-like burning odor in the cockpit. The co-pilot contacted the lead flight attendant, who confirmed that a similar smell was present in the rear of the cabin.
In response to the odor, the crew declared a Mayday. The co-pilot donned an oxygen mask. As the aircraft continued its approach and the flaps were set to position 2, the odor intensified. The lead flight attendant then reported visible smoke in the aft cabin, prompting her to instruct passengers to breathe through cloths. The pilot in command notified Air Traffic Control that smoke was now visible and requested that airport fire services and mobile stairs be on standby upon arrival.
The aircraft landed safely on runway 33 and taxied to stand E3. After stopping the engines and starting the APU, the crew prepared passengers for a potential evacuation. Ultimately, the pilot decided on a controlled disembarkation via mobile stairs at door 1L. No injuries were reported, and no fire was found in the cabin upon ground inspection.
The investigation
The BFU examined the aircraft's technical logs and the components of the air conditioning system. The maintenance provider inspected the left-side air conditioning pack (PACK No. 1) and identified a faulty air-cycle machine (ACM) as the source of the smoke and odor. The investigation focused on the internal mechanics of the ACM, specifically the compressor shaft, turbine housing, and bearings.
Findings
- The primary cause of the smoke and odor was the failure of an air bearing on the turbine side of the air-cycle machine.
- This failure caused the pressure plate to rub against the turbine wheel at high rotational speeds, leading to overheating.
- The resulting imbalance caused the compressor shaft to strike the inner wall of the turbine housing, creating visible wear and friction marks.
- The maintenance inspection confirmed that the failure of the air bearing led to the observed mechanical degradation and subsequent smoke production.