What happened
On 28 February 2020, a Boeing 737-8B6, registration CN-RGJ, was performing a commercial passenger flight from Casablanca to London Gatwick. During the takeoff roll on runway 2/26L, the crew expected the automated "V1" callout; however, this announcement failed to occur. Upon checking the Primary Flight Display (PFD), the commander discovered that the V-speed bugs were not visible on the airspeed tape.
As the takeoff progressed, the commander noted the aircraft felt slow and continued the acceleration to evaluate the situation. Consequently, the aircraft rotated at 189 kt, which was 37 kt above the calculated rotation speed. The aircraft became airborne approximately 120 m before the end of the runway, 13 seconds later than the planned rotation time. There were no injuries and no damage to the aircraft.
The investigation
Investigators examined the Flight Management Computer (FMC) data and Quick Access Recorder (QAR) logs. The investigation established that while the aircraft weight and assumed temperature had been entered into the FMC, the V-speeds were entirely absent from the system during the takeoff roll. The QAR confirmed that the V-speeds were blank from the start of the engine start sequence through the taxi and takeoff.
Technical analysis of the Boeing 737-8B6 systems showed that if V-speeds are deleted after being entered, the aircraft should trigger specific amber warnings on the CDU and a "no vspd" message on the PFD. The manufacturer could not identify any method for deleting these speeds without such alerts. The investigation also noted that the operator's subsequent checks of the aircraft's technical logs and previous/subsequent flights showed no hardware faults, as the automated calls functioned normally on other sectors.
Findings
- The takeoff speeds were not present in the FMC during the departure.
- It is likely the crew either failed to enter the speeds or inadvertently deleted them during the preflight process.
- The aircraft rotated significantly above the intended speed due to the crew's delay in reacting to the lack of automated callouts and the absence of speed bugs.
- The crew's reliance on the normally reliable automated systems contributed to the delay in recognizing the missing data.