Description

On 14 January 2013, an ATR72-212 (E7-AAD) being operated on a passenger flight from Sarajevo to Copenhagen left the side of the runway at high speed shortly after touchdown on runway 22L at Copenhagen in day Visual Meteorological Conditions (VMC). After travelling on the grass and decelerating for approximately 350 metres, the aircraft regained the runway. After a visual inspection by the airport Rescue and Fire Fighting Services to confirm that no obvious damage had been sustained, the aircraft was taxied to the terminal. The aircraft was subsequently confirmed to be undamaged and there were no injuries to the 42 occupants.

Investigation

An Investigation was carried out by the Danish AIB. It was noted that both pilots had similar and significant experience, almost all of it gained on the ATR-72 in both cases. The aircraft commander had been PF for the landing.

It was established that shortly after touchdown and in accordance with normal procedure, the PF had selected Power Levers to Ground Idle but that only the left engine had engaged as commanded and the aircraft began to veer to the left. This situation was clearly indicated by the absence of a 'LO PITCH' light for the right engine. However as the First Officer called out in accordance with routine procedure for this eventuality and twice in succession "one low pitch", the commander selected both power levers into reverse. As a consequence, and despite the prompt reversion from reverse to ground idle, the veer to the left had already increased and he was unable to prevent the aircraft departing the 45 metre wide runway onto the adjacent short grass about 1250 metres from the runway threshold. It continued on the grass for approximately 350 metres tracking up to 17.5 metres beyond the edge of the runway before control was regained and it re-entered it. It was then taxied slowly to a nearby taxiway and after an external visual inspection by the RFFS found no obvious damage, was taxied to the assigned gate for passenger disembarkation.

It was subsequently confirmed that the aircraft had sustained no damage and also that the excursion had not resulted in any damage to the runway edge lighting - both exit from and re-entry to the runway had occurred clear of these lights which had remained to the right of the aircraft as it travelled on the grass.

The ATR 72 Flight Crew Operating Manual (FCOM) was found to contain a clear procedure requiring confirmation of transition to low pitch after movement of the Power Levers from the Flight range to the Ground (Beta) range after landing and to also include a specific Caution that selection of reverse was "not allowed" if either 'LO PITCH' light is not illuminated.

Examination of the Propeller Electronic Computer (PEC) for the right engine found that it has recorded two fault codes. These both confirmed the indicated failure to the ground fine pitch system and would have appeared when the corresponding Power Lever had been moved below flight idle and the propeller blade pitch did not follow the command. Aircraft Maintenance Manual trouble shooting guidance was followed but no hard faults were found. The PEC failure codes were reset and an engine ground run confirmed that the operation of the propeller control system was normal.

The Conclusion of the Investigation was that:

"Upon landing the right hand PEC system failed. (With only one LO PITCH light illuminated, reverse pitch was selected contrary to SOP) and together with (a) left hand crosswind component of 16 knots, worsened the asymmetric forces to the left".

The Final Report of the Investigation was published without the inclusion of any Safety Recommendations .

Further reading

• Runway Excursion
• Standard Operating Procedures (SOPs)
• Throttle Lever
• Alpha Range
• Beta Range
• Single Event Effects (SEE) on Aircraft Systems caused by Cosmic Rays, EASA Safety Information Bulletin