What happened
On December 24, 1997, at approximately 06:15 local time, a Finnair Saab SF340, registration OH-FAB, operating flight FIN 258 from Pori to Helsinki, breached its assigned altitude. While flying through the Tampere Area Control Center (ACC) airspace, the aircraft climbed to flight level 120, exceeding its cleared flight level of 110.
During the pre-departure phase at Pori, the flight crew requested a direct routing to Helsinki. The Pori controller provided both taxi and route clearances simultaneously. While the first officer recorded the clearance, the captain—who was actively maneuvering the aircraft in dark, wintry conditions—manually adjusted the altitude preselector. During this process, the captain incorrectly set the altitude to 110 instead of the required 110.
After takeoff, the aircraft climbed through flight level 65 and eventually reached flight level 120 at 04:15 UTC. The error was not identified during the cockpit checks. The breach lasted for approximately five minutes and ten seconds before the crew was notified by the area controller and began descending back to the assigned flight level 110.
The investigation
The investigation examined the actions of the flight crew, the Pori local controller, and the Tampere ACC controller. Investigators reviewed radio communications, radar recordings, and cockpit procedures. The investigation also looked into the crew's fatigue levels, noting that the crew had experienced a "short night" with only about four hours of sleep in a hotel prior to the flight. Additionally, the investigation compared this incident to three similar altitude preselector errors involving the same operator within a short period.
Findings
- The primary cause of the incident was that the captain incorrectly set the altitude preselector to flight level 120.
- Cockpit cross-checking procedures failed to detect the incorrect setting during the pre-flight and taxi phases.
- The captain's attention was divided between maneuvering the aircraft in difficult visibility conditions and adjusting cockpit controls.
- The crew was likely experiencing reduced alertness due to a lack of restorative sleep following a short night.
- The Pori controller provided the route clearance during the taxi clearance, and the first officer did not read back the altimeter setting, which the controller did not specifically demand.
- There was no risk of collision with other traffic during the breach.