What happened
On 21 July 2017, a Boeing 737-86J, registration C-FWGH, was performing a takeoff from runway 07 at Belfast International Airport. During the takeoff roll, the aircraft failed to accelerate at the expected rate. As the aircraft approached the end of the runway, the crew became aware that the runway limit was approaching much sooner than anticipated relative to their current speed. The aircraft eventually reached the end of the runway, resulting in a serious incident.
The investigation
The AAIB investigation focused on the performance data programmed into the aircraft's systems prior to departure. Investigators examined the Flight Management Computer (FMC) and the Electronic Flight Bag (EFB) data to determine why the takeoff performance was compromised. The inquiry looked into the accuracy of the Outside Air Temperature (OAT) entries and how these figures were cross-checked by the crew. Additionally, the investigation reviewed the crew's response to the lack of acceleration and evaluated the human factors involved in recognizing the performance discrepancy during the critical takeoff phase.
Findings
- The primary cause of the insufficient acceleration was the erroneous entry of takeoff performance data into the Flight Management Computer.
- An error occurred during the input of the Outside Air Temperature (OAT) into the FMC, which led to incorrect thrust settings being calculated and applied.
- The crew did not identify the incorrect thrust settings during the pre-flight or before-start phases.
- The feedback from the aircraft's systems regarding the thrust setting was opaque, making the error difficult to detect once the takeoff roll had commenced.
- The crew's reaction—failing to manually increase thrust—was influenced by standard operating procedures and training, which emphasize not manipulating thrust levers after reaching V1, and a lack of familiarity with manual thrust intervention in such scenarios.