What happened
On 19 August 2012, an ATR 72-212A operated by Flybe Finland Oy, registration OH-ATH, veered off runway 2HM during its landing roll at Helsinki-Vantaa airport. The aircraft was performing a scheduled flight from Tampere-Pirkkala.
During the approach, the automatic function of the Travel Limitation Unit (TLU)—a system designed to limit rudder deflection—malfunctioned. The flight crew did not activate the TLU standby system. Because the landing criteria outlined in the Quick Reference Handbook (QRH) for a TLU failure were still met, the captain proceeded with the landing. Upon touchdown, the captain noted that the rudder pedals felt stuck. Due to the lack of rudder authority, the aircraft drifted off the runway onto the shoulder strip. The captain was eventually able to use nose wheel steering to guide the aircraft back onto the runway. There were no injuries to the 27 passengers or four crew members, and no damage was sustained by runway equipment.
The investigation
The investigation examined the mechanical failure of the TLU system, the crew's response to the malfunction, and the impact of human factors. Investigators analyzed flight data recorder (FDR) information to understand the aircraft's abnormal movement and the sequence of events during the landing roll. The probe also looked into the clarity of the QRH instructions and the crew's system awareness during a high-stress situation.
Findings
- The direct cause of the excursion was insufficient rudder authority to maintain directional control, as the rudder was mechanically limited to the center position.
- The TLU's automatic actuator electric motor failed, causing the system to remain in the high-speed (HI SPD) mode, which restricted rudder movement.
- The crew failed to engage the TLU standby system due to inadequate system knowledge and unclear instructions within the QRH.
- A contributing factor was an asymmetrical propeller blade angle transition into the beta zone during power reduction, which caused a significant lateral oscillation.
- Additional contributing factors included potential deficiencies in the left braking system and engine power asymmetry during the landing roll.