What happened
On October 30, 2021, a Finnair flight operated by Nordic Regional Airlines (Norra) traveling from Riga to Helsinki experienced an in-flight incident involving an unusual odor in the cockpit. The aircraft, an ATR 72-500 with registration OH-ATG, was carrying 41 passengers and 4 crew members when the flight crew first detected an oily smoke smell at approximately 5,000 feet.
Shortly after takeoff, the aircraft experienced a Digital Air Data Computer (DADC) warning and the autopilot disconnected, forcing the captain to fly manually. While the crew successfully re-engaged the automation, the smell of smoke persisted and recurred later in the climb. Although the crew did not initially use emergency checklists to identify the source, they prepared for a potential diversion to Tallinn.
As the aircraft commenced its final approach to Helsinki-Vantaa at 2,500 feet, the odor became intense. The crew donned oxygen masks and declared a Mayday to air traffic control, intending to stop on the runway for a potential evacuation. Upon landing, the aircraft stopped on the runway, and the crew initiated procedures to prepare passengers for disembarkation. Following the landing, passengers were safely evacuated via the main door to a waiting bus.
The investigation
The investigation examined the technical state of the aircraft, the crew's response to the smoke odor, and the coordination between air traffic control and airport rescue services. Investigators reviewed flight data, cockpit recordings, and interviewed personnel involved in the flight and the emergency response.
Findings
- The oily odor in the cockpit was caused by leaking oil from the left engine's bearing seals. This leak allowed oil to seep into an area where air is drawn into the aircraft's ventilation system. The leak was attributed to the wear of an air switching valve.
- The crew did not initiate smoke emergency checklists when the odor was first detected during the climb. Had these procedures been followed, the entry of the odor into the cockpit might have been prevented.
- There is a high threshold for crews to utilize oxygen masks and smoke goggles during ambiguous or mild odor events, which can delay critical corrective actions.
- During the emergency response, communication between the aircraft and airport rescue services was conducted through air traffic control rather than via a direct radio frequency, which could have improved situational awareness.
- The use of two different rescue leaders (fire chiefs) during the response potentially complicated the overall management of the incident.