Atlantic B462 at Stord on Oct 10th 2006, overran runway and burst into flames
Last Update: April 19, 2012 / 16:32:05 GMT/Zulu time
The Norwegian Statens Havarikommisjon for Transport (AIBN) released their final report concluding the causes of the accident were:
- The approach and landing were normal, within those variations that may be expected.
- None of the aircraft's six lift spoilers were deployed when the commander operated the spoiler lever.
- The AIBN has found two possible explanations for the spoilers not being deployed:
1. A mechanical fault in the spoiler lever mechanism.
2. Faults in two of the four thrust lever micro switches. A fault in one switch may have been hidden right up until a further switch failed.
- The crew received a warning that the spoilers were not deployed.
- The commander noticed that the aircraft was not decelerating as expected. He did not associate this with the fault in the spoilers and assumed that the problem was due to a fault in the brakes. He therefore applied the emergency brakes.
- The emergency brakes do not have anti-skid protection and the wheels locked, so that in combination with the damp runway reverted rubber hydroplaning occurred. Consequently the friction against the runway was significantly reduced.
- The runway was not grooved. The AIBN believes that reverted rubber hydroplaning will not occur, or will be significantly reduced, on grooved runways.
- The aircraft was travelling at approximately 15-20 kt when it left the runway and slid down the slope.
- The AIBN considers that, on its own, the failure of the spoilers to extend would not have caused a runway overrun. The aircraft might have stopped within the landing distance available with a good margin if optimum braking had been used.
- The aircraft sustained serious damage as a result of the uneven terrain and the abrupt stop at the bottom of the slope.
- The aircraft was seriously damaged during the excursion, so that fuel leakage and immediate ignition occurred, most probably due to an electrical short circuit.
- The fire escalated rapidly, because it was supplied with large quantities of fuel from the tanks in the aircraft's wings.
- The inner left engine continued to run at high speed for more than five minutes after the aircraft crashed. This set the surrounding air in motion, so that the fire received a good supply of oxygen.
- The AIBN considers that, in principle, all those involved had a chance of surviving the accident resulting from the excursion.
- Flames spread to the cabin after a very short time.
- The rapid spread and intensity of the fire left very short time margins during the evacuation.
- The survivors evacuated via the left cockpit window and the left rear door. The other doors could not be opened or could not be used as a result of the fire.
- The reinforced cockpit door prevented evacuation via the cockpit. Two persons were found dead in the cabin, behind this door.
- The fire and rescue service were quick to arrive at the end of the runway.
- The fire engines did not come near enough to the fire due to the difficult terrain.
- The jet blast from the running engine was directed towards the fire engines, creating a headwind.
- Even though the fire and rescue service did all they could to contain the accident, the result was that the effort had little effect in the most critical period when the evacuation was in progress.
- In the AIBN's opinion, access for the fire and rescue service is a matter to which larger attention needs to be paid in connection with future assessments of safety areas and unobstructed areas in the immediate vicinity of Norwegian airports.
- The aircraft was registered in accordance with the regulations and had a valid certificate of airworthiness.
- The investigation has not brought forth information to the effect that prior to the accident the aircraft had technical faults or defects that might have had an impact on the chain of events.
- In order for the wheel brakes on the aircraft to be effective at high speeds, the lift spoilers must be extended.
- International statistics show that the aircraft type BAe 146 is no more prone to runways overruns than other aircraft types. However, the aircraft type does not have the option of increasing the safety margins by using reverse thrust.
- The crew had valid licenses and ratings to serve on board.
- The crew had accomplished the company CAA approved and extensive training program.
- The commander had accomplished the training program with normal progress and passed company and CAA examines.
- The commander was experienced on the aircraft type and knew the airport well, but he was relatively new as a commander in the company.
- The flight crew had not been informed that the runway was damp. This follows from BSL E 4-2 which indicates that moisture on the runway is not normally provided to flight crew.
- The decisions made by the flight crew prior to the actual landing and further reaction pattern after the loss of spoilers cannot be related to fatigue and/or lack of vigilance.
- Neither the manufacturer nor the airline had prepared specific procedures stating how the crew should act in a situation where the lift spoilers did not deploy. The pilots had not trained for such a situation in a simulator.
- The AIBN considers that the excursion could have been prevented by relevant simulator training, procedures and a better system understanding related to failures of the lift spoilers and the effect that it has on the aircraftsÂ’ stopping distance.
- At the time of the accident the design of the safety areas at the airport was not in accordance with the applicable requirements in BSL E 3-2.
b) The AIBN believes that there is a possibility that the aircraft might have stopped inside the safety area had the safety area been lengthened by 50 m in accordance with the new requirements in BSL E 3-2.
- The surrounding terrain was significantly steeper than prescribed in ICAO Annex 14 SARPS, and this had been announced for Stord airport in AIP Norway.
- The deviations relating to the airport's safety areas and adjacent terrain were major contributors to the severity of the accident.
- In connection with the renewed approval of Stord Airport SÃ¸rstokken in 2006, DNV undertook a risk analysis of the obstacle situation at the airport. Of the aircraft types that regularly used the airport, the BAe 146 was assessed as having the highest probable accident frequency. Extension of the safety area at the end of the runway was identified as a relevant risk-reduction measure.
- The CAA Norway renewed the airport's technical and operational approval from June 2006 subject to a requirement for improvement of the safety area by October 2008.
- It seems like there was no particular response from Stord Airport, Atlantic Airways or CAA Norway relating to the results of DNV's risk analysis, which showed heightened risk in connection with operations using aircraft type BAe 146.
- CAA Norway did not require compensatory measures to be implemented in response to recognised nonconformities relating to safety areas and the adjacent terrain in anticipation of physical improvements to the airport.
- CAA Denmark and CAA Norway had not, as far as the AIBN is aware, exchanged safety related information about the airport or the airline.
The captain (34, ATPL, 5,000 hours total, 1,500 hours on type) was pilot flying, the first officer (38, ATPL, 1,000 hours total, 250 hours on type) was pilot monitoring. The crew was preparing for a VOR runway 15 approach but expected to become visual with the aerodrome and runway and conclude a visual approach and landing. After becoming visual the crew, who strictly adhered to sterile cockpit requirements, assessed a visual approach to runway 33 was possible despite a small tailwind component and would shorten their approach. The crew therefore decided to land on runway 33 advising Stord's AFIS about their intention. The AFIS officer reminded the crew of the tail wind component.
The captain aimed for one white and three red lights at the runway's PAPI, the first officer called twice the speed was correct. The flight data recorder confirmed the aircraft crossed the runway threshold at the Vref of 112 KIAS, ground speed of 120 knots, at a height of 50 feet. The aircraft subsequently touched down a few meters past the ideal touch down point, still at the aiming marker, both flight crew described the landing as soft. Although the captain pulled the spoiler lever fully aft into the ground spoiler position, the spoiler lights did not illuminate, the flight data recorder confirmed none of the six spoilers had deployed. When the spoiler lights did not illuminate the first officer called out "NO Spoilers" and verified that hydraulic pressure and other instruments showed normal values, while the captain was attempting to apply full brakes pressure, switched the brakes from green to yellow hydraulics and subsequently to emergency brakes disabling antiskid. When the captain realized he would not be able to stop the aircraft before the end of the runway he attempted to bring the aircraft into a position to skid sidewards hoping to increase friction that way. The aircraft overran the end of the runway at about 15-20 knots and followed down a steep slope, the gear doors were torn away, engine #4 (outboard right) was ripped off the wing, the right wing received several cuts due to impact with trees and approach lights. The nose subsequently impacted rising ground at relatively high speed causing deformations and distortions of the nose section that jammed the door between cockpit and cabin. Passengers observed sky through an opening in the roof, one passenger was showered with fuel. The crew did not succeed in shutting engine #2 down suggesting the connection between the fuselage and wing was broken. Fire broke out immediately after the aircraft came to rest, a tear in the fuselage caused the fire to spread quickly from the outside to the inside of the cabin. Both forward left hand and right hand doors could not be opened even by brute force being blocked by terrain. The left inner engine #2 continued to run leaving the aft flight attendant in doubt whether to begin evacuation or not. The flight crew attempted to evacuate via their normal escape route through the cockpit and attempted to open the re-inforced door however unsuccessfully, after two attempt the crew gave up and climbed to safety through the left hand cockpit side window. While flight attendant #2 managed to open the left rear door, a passenger opened the right rear door with great effort but confirmed the fire was too intense to evacuate via that door. The left inboard engine created noise, heat and wind to those who evacuated through the left hand rear door. Emergency vehicles were not able to get any closer than 65 meters to the aircraft due to terrain, fire fighters needed to connect hoses and create a pipe down to the wreckage which arrived after the passengers had evacuated.
Two fatalities were found in the cabin right behind the cockpit door, the other two in the forward section of the cabin.
The AFIS officer at Stord Airport later said he observed wake vortices off the wings during the rollout of the aircraft.
The flight data recorder was damaged, the AIBN therefore had limited access only to data. In addition the AIBN was unable to determine the status of the runway at the time of the accident, in particular how damp the runway had been.
The AIBN analysed that the nose wheels touched down before or at the same time as the main gear. The non-illumination of the spoiler lights suggests that none of the spoilers deployed leaving the wings produce significant lift with low weight on the main wheels resulting in less braking action than required, wake vortices off the wings and screeching tyres. The commander got soon aware that brakes were not working as expected and began to select alternate braking. After the emergency brakes got selected and the antiskid system was thus disabled the wheel brakes locked giving rise to reverted rubber hydroplaning, traces of which could be found starting 945 meters past the runway threshold and right to the end of the runway where the aircraft went down the slope, the AIBN therefore holds the opinion "the aircraft skidded with locked wheels along the last 520m of the runway length."
The AIBN analysed that the failure of the spoilers to lift was decisive for the chain of events. Despite signficant resources devoted to the examination of the spoiler system the investigation did not find any indication of any faults in the spoiler or associated systems. As both green and yellow spoilers are entirely independent two independent failures would be required to fail both systems. The AIBN stated it was "improbable that two such independent faults could arise simultaneously in relatively reliable systems, and give little weight to such a possibility".
The fault analysis therefore focussed on three possible scenarios:
Linkage failure of the spoiler lever: this would have illuminated two orange/magenta spoiler lights, that were improbable to be missed by the flight crew.
Failure of two thrust lever microswitches: If one microswitch fails, it will only be detected by a maintenance inspection, but remain dormant until a second microswitch fails and inhibits the deployment of spoilers. With two microswitches failed one orange/magenta spoiler light will illuminate, the crew however did not observe any such light.
Circuit breakers in green and yellow system open: the AIBN analysed this was highly unlikely due to warnings associated with it as well as preflight inspection and lack of maintenance actions. The AIBN ruled this option out as a possible explanation.
Due to the damage to the flight data recorder the AIBN could not rule out other possibilities why the spoilers did not extend. The AIBN analysed: "On the basis that the AIBN has been unable to determine the exact cause for the spoilers not extending, the AIBN considers that there are insufficient grounds for submitting a safety recommendation to BAE Systems concerning the design and maintenance of the spoiler system."
The AIBN reported that the captain voiced the opinion in his interview after the accident, that he would have been able to stop the aircraft on a runway offering 50 to 100 meters more length. The first officer believed 10-15 meters of additional pavement would have been sufficient to stop the aircraft.
The AIBN analysed that Stord's runway 33 had a runway safety end area of 130 meters while ICAO required a runway end safety area of 180 meters for runways of 1200 meters and longer. In addition the terrain around was signficantly steeper than prescribed by ICAO, this was announced in the AIP. In the meantime the runway end safety area has been extended to 190 meters besides a number of other measures to improve the airport. Nonetheless, the AIBN "can absolutely see that an energy absorbing system (EMAS, see subsection 1.18.4) can and should be used where the necessary space for establishing satisfactory safety areas at the ends of runways is lacking."
This article is published under license from Avherald.com. © of text by Avherald.com.
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