Safety margins at Stord Airport were insufficient
From the report released today:
At the time of the accident, the runway was 1,460 m long and 30 m wide. Both thresholds 20 were 130 m from the asphalt edges. The landing distance available (LDA) was stated to be 1,200 m for both runway directions and the take-off distance available (TODA21) was stated to be 1,330 m for both runway directions. This means that at both ends of the runway there was a paved safety area of 130 m. Beyond the safety areas, there was a steep downhill slope in both runway directions. OY-CRG ran off the runway at the north-western end.
SUMMARY
During normal approach and landing at Stord Airport Sørstokken OY-CRG ran off the runway and plunged down a steep slope. The aircraft sustained considerable damage and caught fire immediately. The fire spread so fast that there was not enough time for everybody to evacuate the aircraft. Four people died and six were seriously injured. In its investigation of the accident, the AIBN found that several factors contributed to the accident. The accident was initiated when none of the aircraft's six lift spoilers were deployed after landing.
The AIBN believes it has found two possible technical reasons for this. The wings continued to produce lift, so that the weight of the aircraft was not sufficiently transferred to the landing wheels. Hence, the main wheels did not get sufficient contact with the runway and the braking effect was reduced. The pilots perceived this as wheel brake failure and the emergency brakes were engaged. The emergency brakes do not have anti-skid protection, and the wheels locked. In combination with the damp runway this led to 'reverted rubber hydroplaning' (the rubber in the tyres started boiling), and the aircraft was unable to stop on the runway.
The AIBN believes that the lift spoilers’ failure to deploy in isolation would not have caused the aircraft running off the end of the runway. The aircraft could have stopped within the available runway length if optimum braking had been utilised. The AIBN therefore considers that the excursion could have been prevented by a better system understanding related to failures of the lift spoilers and the effect that it has on the aircrafts’ stopping distance.
The AIBN also believes that grooves in the runway surface could have improved the braking action in this case. The accident has shown that the safety margins at Stord Airport were insufficient. The paved safety area did not extend far enough past the end of the runway in accordance with the requirements of Norwegian BSL E 3-2 and ended in a slope that was steeper than prescribed. These deficiencies were major contributors to the severity of the accident.
The topography caused the aircraft to catch fire. Moreover, the steep terrain was an obstruction to the fire-fighting and rescue work. The AIBN sees this accident as the accumulated effect of three factors – the aircraft design, the airport and operational factors, which, seen as a whole, may have been unacceptable at the time of the accident. The AIBN submits two safety recommendations on the basis of its investigation of this accident.
Last edited by Jetdriver; 24th Apr 2012 at 15:23.