What happened
On 16 November 2017, a Boeing B737-700, registration VP-CAM, prepared for a non-scheduled flight from Seletar Airport, Singapore, to Beijing, China. During the takeoff roll on Runway 03, the aircraft utilized a thrust setting that was insufficient for the prevailing environmental conditions and the available runway length.
As the aircraft accelerated, the tower controller observed a shallow climb angle and noted that the aircraft lifted off very close to the runway end. Following the departure, a runway inspection revealed that 10 approach lights at the end of Runway 03 had been damaged, with several supporting structures broken. Upon arrival in Beijing, the aircraft's left main landing gear tires were found to have sustained cuts and gouges. There were no injuries to any persons on board.
The investigation
The investigation focused on why the aircraft's takeoff performance was compromised. While the flight crew used the Onboard Performance Tool (OPT) to calculate takeoff speeds, they relied on the Flight Management Computer (FMC) for the final takeoff settings. The investigation found that an incorrect assumed temperature of 67°C had been inadvertently entered into the FMC. This high assumed temperature caused the FMC to calculate a reduced thrust setting of 90.4% N1, which was significantly lower than the required power for the day's conditions.
Investigators also examined the discrepancy between the OPT and the FMC. Unlike the OPT, the FMC does not incorporate runway length into its performance calculations, meaning it did not alert the crew that the reduced thrust setting was unsafe for the specific runway length at Seletar Airport. The crew also failed to notice a "VERIFY TAKE-OFF SPEEDS" message on the CDU during taxiing, and they did not identify the mismatch between the OPT and FMC results during their pre-flight preparations.
Findings
- The aircraft performed a takeoff using a reduced thrust setting that was far below what was necessary for the aircraft's weight and the available runway.
- An incorrect assumed temperature of 67°C was erroneously introduced into the FMC.
- The flight crew did not identify the significant differences between the performance calculations provided by the OPT and the FMC.
- The FMC lacks the capability to cross-reference takeoff calculations with available runway length, unlike the more sophisticated OPT.
Safety action
Following the incident, the operator implemented new procedures requiring the Pilot Monitoring to verify that the N1 value matches the OPT calculation before announcing "Thrust Set." The operator also reinforced instructions to avoid the Assumed Temperature method and to use maximum thrust on runways shorter than 1,830 m. Additionally, the aircraft manufacturer issued a technical bulletin to assist operators in verifying takeoff performance data.