What happened
On 15 September 2016, an AVRO 146-RJ100, registered HB-IYW, was prepared for departure from Nuremberg Airport for a scheduled flight to Zurich. During the pre-departure phase, the flight crew activated the auxiliary power unit (APU) to provide cabin cooling due to high external temperatures. Shortly after activating the air conditioning packs, the crew detected an oily smell in the cockpit and subsequently deactivated the APU.
During the takeoff roll and initial climb, the crew continued to operate the aircraft using only one air conditioning pack, supplied by engine bleed air. Approximately two minutes after takeoff, the copilot detected a sweet, oily odor. In the interest of safety, the flight crew donned oxygen masks. Despite being questioned twice by air traffic control regarding whether they intended to declare an emergency, the crew requested priority and continued the flight to Zurich.
Upon arrival in Zurich, the aircraft landed using an autoland procedure. While the cabin air remained acceptable to the cabin crew, the flight crew had remained on oxygen. The fire service inspected the aircraft upon arrival but found no evidence of contamination or mechanical issues.
The investigation
STSB investigators examined the aircraft's air conditioning configuration and the source of the odor. Maintenance inspections included borescope examinations of engines 1 and 2, searches for contamination around the APU, and testing the air conditioning packs using an aerotracer device. While technicians replaced cabin and cockpit filters and repaired a small oil leak in an integrated drive generator, these efforts were inconclusive. A subsequent test flight was conducted with all air conditioning configurations activated, which failed to replicate the odor.
Findings
- The crew's decision to switch rapidly between air conditioning packs and deactivate the APU prevented a systematic identification of the odor's source.
- The crew's decision to continue the flight while wearing oxygen masks was questionable, as the single active air conditioning pack supplied air to both the cockpit and the cabin.
- The decision to continue the flight may have been influenced by a lack of definitive findings in previous similar incidents involving unidentifiable odors in the AVRO fleet.
- The crew's choice to proceed was motivated by a desire to avoid passenger delays and protect connecting flights.