What happened
On the morning of 22 April 2025, a Boeing 737-8 registered as G-CRUX was preparing for a scheduled commercial passenger flight to Athens from London Luton Airport. The crew had initially planned to depart using the full length of Runway 25 but subsequently accepted an intersection departure at Intersection ‘A’. During pushback, the pilots informed air traffic control that they were able to accept this shorter runway configuration.
As the aircraft approached the holding point, the crew believed they had updated the critical takeoff speeds in the Flight Management Computer (FMC) based on their Onboard Performance Tool calculations. However, flight data monitoring analysis later revealed that the maximum thrust used during the takeoff roll was only 82.1%, significantly lower than the 85.2% required for the shorter runway segment. Consequently, the aircraft rotated with fewer than 162 meters of paved runway surface remaining. The climb-out was notably shallow, with the aircraft crossing the end of the runway at an altitude of just 13 feet above ground level. Radar data indicated that the aircraft was still climbing through 900 feet at a distance of approximately 0.8 nautical miles from the airfield, a trajectory much further out than typical for this type of departure.
The investigation
The Air Accidents Investigation Branch examined the flight data to understand why the performance settings did not match the accepted runway configuration. It was established that while the crew had checked their calculations to see if an intersection departure was possible, they failed to verify that the takeoff performance data entered into the FMC actually reflected the shorter Take-Off Run Available (TORA) of 1,771 meters associated with Intersection ‘A’. Instead, the system retained settings aligned with the full runway length of 2,116 meters. The investigation highlighted that the V2 speed was not changed between the initial data entry during flight preparation and the actual takeoff, leading to the incorrect thrust setting.
Findings
The primary causal factor was the crew's acceptance of a change to the planned departure point without verifying that the takeoff performance parameters were correctly updated in the aircraft's systems. This oversight resulted in a lower power setting than required for the shorter runway segment, causing an extended takeoff roll and a slow climb-out. The investigation noted that had there been a loss of thrust during this phase, the aircraft might not have been able to stop on the remaining paved surface if the takeoff was rejected, or it might have failed to achieve minimum obstacle clearance heights if the takeoff was continued.
Safety action
Following the incident, the operator reviewed its internal procedures regarding intersection departures and performance data entry. New guidance has been issued to flight crews to ensure that changes to departure points are rigorously verified against the aircraft's performance settings before takeoff.