On 8 January 2010, a Boeing 737-800 being operated by Air Berlin on a scheduled domestic passenger flight from Nuremburg to Düsseldorf left the snow-covered runway 10 shortly after attempting to begin a rolling take off in normal night visibility after less than normal braking action had been notified. The aircraft was not damaged and an emergency evacuation was not necessary. None of the 131 occupants was injured
An Investigation was carried out by the Bundesstelle für Flugunfalluntersuchung (Germany) (BFU) and SSFDR and Cockpit Voice Recorder (CVR) data was successfully downloaded and used to assist the Investigation. It was noted that the crew was experienced and that the flight being operated had been delayed by an hour.
It was noted that the 50 year-old Captain had a total of 5,291 flying hours of which 3 720 hours were on type. The 39 year-old First Officer had a total of 4,603 flying hours of which 1,738It were on type.
It was established that the aircraft had left the side of the runway after about 150 metres and had come to a stop about 5 metres to the right of it with the wheels of the nose and the main landing gears having sunk into the soft ground by about 15 cm. On the runway, all three landing gears had left marks in the accumulated snow.
An air temperature of -5º with light snow was recorded as falling at the time of the excursion with an observed accumulation on the 38metre cleared width of the 45 metre wide runway surface of 2mm following completion of snow clearance a few minutes earlier. Braking action had been advised to the incident aircraft crew as ‘Medium’ as they were transferred from ‘GND’ to ‘TWR’ when approaching the runway. The current Meteorological Terminal Air Report (METAR) had included a mean surface wind velocity of 10 knots directly across the runway from the left.
As alignment on the centreline was attempted with the aircraft still accelerating, both main landing gear wheel assemblies crossed the runway centre and when this was countered with a turn to the right, it was then found that it was not possible to steer to the left. With the aircraft on a heading of 120º and about to leave the runway at a ground speed of 17 knots, the thrust levers were retarded and the aircraft came to a stop soon afterwards.
FDR data also showed that engine thrust had not been symmetrically applied - the left engine had always been set higher than the right - and it was considered that “even though the difference was marginal with a slippery ground this can already have an influence on distance and direction”.
Overall, it was considered that the unstable line-up had been the direct consequence of inappropriate crew actions and that “given the wintry conditions a safe and controlled take-off run was no longer possible”.
It was found that two generally applicable Operations Manual procedures had not been followed - when to power up for rolling take offs and the maximum ground speed whilst turning onto the runway. Thrust had been increased to 43% N1 with 80º of the right turn onto the runway centreline still to go and as a consequence, ground speed reached almost double the maximum 10 knots permitted.
It was also found that Boeing FCOM Supplementary Procedures “issued for the Operator” contained an applicable variation on this normal initiation of the take off roll applicable to departures made in icing conditions which expressly required a standing start take off preceded by a static engine run up to “a minimum of 70% N1 for approximately 30 seconds and confirm stable engine operation before the start of the takeoff roll”. Clearly, this requirement had been either ignored or unknown to the crew involved.
It was concluded that the Cause of the incident was “the increased ground speed during line-up on a snow-covered runway”. The Investigation also identified the following four Contributory Factors:
- The rolling take-off was not conducted according to OM/B requirements.
- The procedure "static run-up" was not conducted even though, given the weather conditions, it would have been necessary.
- The continuously falling snow resulted in snow-covered operating areas in spite of continued snow clearing services.
- The published procedures for "adverse weather" and "initiating take-off roll" according to OM/B and FCOM were not conducted.
The following two Safety Recommendations were issued as a result of the Investigation:
- that the Operator should incorporate the procedure "static run-up" into the OM/B item 2.3 as take-off procedure (besides "rolling take-off" and "standing take-off") as described in the FCOM; so far it is only a Note. [24/2010]
- that the Operator should ensure that all crews are familiar with the corresponding Cold Weather Operations. During the semi-annual simulator training and the respective check flights (OPC/LPC) Cold Weather Operations and their corresponding procedures should be trained and checked. In addition, take off runs and abortions on short runways with the corresponding maximum take-off weight in wintry conditions and with contaminated runways should be trained during simulator training. Furthermore, the training personnel should check these procedures in the scope of standardisation / quality assurance during regular flights. [25/2010]
It was noted that Air Berlin has already implemented both these safety recommendations.
The Final Report of the Investigation BFU 5X002-10 was completed on 2 April 2012 and subsequently made available in English translation.