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ASN Wikibase Occurrence # 199853
Last updated: 15 December 2017
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Date:21-JUL-2017
Time:15:39 UTC
Type:Silhouette image of generic B738 model; specific model in this crash may look slightly different
Boeing 737-86J (WL)
Owner/operator:Sunwing Airlines, opf Thomson Airways
Registration: C-FWGH
C/n / msn: 37752/3835
Fatalities:Fatalities: 0 / Occupants: 185
Other fatalities:0
Airplane damage: None
Category:Serious incident
Location:Belfast International Airport (BFS/EGAA) -   United Kingdom
Phase: Take off
Nature:International Scheduled Passenger
Departure airport:Belfast International Airport (BFS/EGAA)
Destination airport:Corfu International Airport (CFU)
Investigating agency: AAIB
Narrative:
Thomson Airways flight BY1526, a Boeing 737-800, damaged a runway approach light following a long takeoff from Belfast International Airport.
The aircraft was operated by a Canadian airline, Sunwing Airlines, on behalf of Thomson Airways on a flight from Belfast International Airport to Corfu, Greece.
The crew boarded the aircraft and completed their pre-flight preparations before pushing back, intending to depart from runway 07. After pushing back, the ground crew noticed that one of the tyres on the nose landing gear was worn and the aircraft returned to the stand.
After both nose landing gear tyres had been changed, the aircraft once again pushed back and taxied out for departure.
The crew were cleared for takeoff on runway 07 from taxiway D, which gave a Takeoff Run Available (TORA) of 2,654 m. During the takeoff, at around 120 to 130 kt, the crew realised that the aircraft was not accelerating normally. They estimated, during post-flight interviews, that they reached V1 with around 900 m of the runway remaining and rotated shortly afterwards. The aircraft was seen, by multiple witnesses, during rotation and took a significant time to lift off before climbing at a very shallow angle.
After the takeoff, airport operations staff conducted a runway inspection and a runway approach light for Runway 25 was found to be broken. Preliminary evidence indicated that the aircraft struck the light, which was 35 cm high, 29 m beyond the end of the runway in the stopway. After takeoff, the crew checked the aircraft's FMC which showed that an N1 of 81.5% had been used for the takeoff. This figure was significantly below the required N1 setting of 93.3% calculated by the operator and shown on the pre-flight paperwork.

Independent assessments by the AAIB and operator showed that the only credible way for this to have happened was for an error to have been made whilst entering the Outside Air Temperature (OAT) into the FMC. If the top-of-climb OAT was mistakenly inserted into the OAT field on the n1 limit page (a figure of -52C as opposed to +16C), and the correct assumed temperature of 48C was entered, the FMC would have calculated a target takeoff N1 of 81.5%.
It appeared that the FMC software version fitted to C-FWGH, U10.8A, predated revision U12.0, which features a crosscheck between the OAT entered by the crew and that sensed by the external temperature sensor.

Further investigation will consider how such a data entry error could have been made, and whether actual aircraft performance matched that which would be expected given the N1 power setting used.

Sources:

https://assets.publishing.service.gov.uk/media/59c2302140f0b60d848fd9ad/AAIB_S2-2017_C-FWGH.pdf


Images:


Groundspeed data for the takeoff in relation to V1 and Vr (AAIB / 2017 Google, Image 2017 DigitalGlobe)


Vertical profile for the initial climb-out (AAIB / 2017 Google, Image 2017 DigitalGlobe)

Revision history:

Date/timeContributorUpdates
20-Sep-2017 19:51 harro Added
20-Sep-2017 20:40 Iceman 29 Updated [Source]
21-Sep-2017 07:34 harro Updated [Source, Narrative, Photo, ]
21-Sep-2017 07:35 harro Updated [Photo, ]

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