What happened
On 11 December 2006, at approximately 20:56, a Finnish Commuter Airlines ATR 42-500, registration OH-ATB, was performing a scheduled flight from Helsinki to Kokkola with a stopover in Seinäjoki. The aircraft was approaching runway 32 in darkness under cloudy and humid conditions. At the time of approach, the wind was reported as 180 degrees at 12 knots, with gusts up to 22 knots.
The captain elected to land on runway 32, as the most recent wind information did not exceed the aircraft's manual limitations. During the landing roll, approximately halfway through the deceleration, the aircraft was struck by a strong gust of wind from the left. This caused the aircraft to veer unexpectedly toward the left side of the runway.
Despite efforts by the crew to correct the direction, the aircraft drifted off the 30-meter wide paved surface onto a 2.5-meter wide gravel shoulder. The left main landing gear traveled approximately 115 meters on this shoulder, reaching a maximum of about 2 meters from the edge of the pavement. During this excursion, the landing gear struck two runway edge lights, destroying one and tilting the other. The impact severed the wiring for the left main landing gear anti-skid system. The captain eventually managed to steer the aircraft back onto the runway and taxied to the apron. There were no fatalities or injuries among the 27 passengers and 3 crew members on board.
The investigation
The investigation examined the aircraft, the weather conditions, and the crew's actions. The investigation established that there were no mechanical defects in the aircraft that contributed to the event. The runway was wet, though braking action was reported as good. Investigators also reviewed the crew's performance, noting that the captain's blood alcohol level was 0.00%. The investigation also noted that the flight data recorder (DFDR) was non-functional, potentially due to improper installation.
Findings
The excursion was caused by a chain of interrelated factors:
- The decision to perform a downwind landing.
- A strong left gust during the landing roll that unexpectedly changed the aircraft's direction.
- The wet runway surface, which facilitated a lateral skid.
- Insufficient runway width to allow for effective correction of the aircraft's path.
- Ineffective use of the rudder as the aircraft's speed decreased.
- A delay in engaging nose wheel steering because the captain did not hear the co-pilot's "70" knot call.
- The captain's limited experience as a pilot-in-command of the ATR type.