What happened
On May 30, 2017, an Airbus A319-111, registration HB-JYK, was operating a scheduled flight from Thessaloniki, Greece, to Basel, Switzerland. Shortly after climbing through 7,000 feet, the flight crew detected a strong, unpleasant odor described as similar to a dirty oven. The smell was also noted in the forward galley by the cabin crew.
In response to the odor, the pilots donned oxygen masks and initiated emergency procedures. After leveling off at 10,000 feet, the crew declared a 'Pan Pan' followed by a 'Mayday' signal, notifying air traffic control of their intention to divert back to Thessaloniki. The crew implemented smoke and fumes checklists, which included switching off the number one air conditioning pack and eventually both packs. To introduce fresh air, they opened the ram air supply and the outflow control valve. The aircraft landed safely at Thessaloniki runway 16 without further incident.
The investigation
The Swiss Transportation Safety Investigation Board (STSB) examined the event, noting that maintenance messages for a vent blower fault and air pack faults were recorded during the flight. While the avionics blower fan assembly was replaced and inspected by the manufacturer, no specific mechanical failure was found during the shop inspection.
However, the investigation highlighted a broader industry context involving the same component. Airbus had previously identified that the avionics blower fan, supplied by a third party, was prone to premature failures due to issues in the repair process, specifically regarding ball bearing quality and improper assembly.