What happened
On 24 April 2019, an Airbus A320-214, registration G-EZTD, was preparing for a commercial passenger flight from Lisbon Airport to London Luton Airport. During pre-flight preparations, the flight crew initially planned to depart from the intersection of Runway 21 and Taxiway U5. However, during subsequent re-planning, the crew decided to use the intersection of Taxiway S1 with the runway.
When recalculating the takeoff performance using the Electronic Flight Bag (EFB), the crew selected a reference point labeled 'PSNSTMP'. They believed this selection corresponded to the S1 intersection; however, this label actually referred to the full length of the runway (the S4 intersection). Because the crew did not cross-check the available takeoff run against the aerodrome ground chart, they failed to notice that the performance figures were based on a runway length 1,395 m longer than what was actually available at their chosen departure point.
As a result, the aircraft departed from the U5 intersection using an engine thrust setting intended for a much longer runway. During the takeoff roll, the commander noted that the acceleration "felt wrong," but the crew did not select Takeoff/Go-around (TOGA) thrust. The aircraft became airborne 400 m before the upwind runway threshold, passing it at a height of approximately 100 ft aal.
The investigation
The AAIB investigation, delegated by the Portuguese authorities (GPIAAF), examined flight data from the FDR and digital access recorder, as well as the aircraft's EFB software. The investigation focused on the nomenclature used within the EFB and the discrepancy between the airport's 'Position' system and standard taxiway naming. The investigation also noted that an identical incident involving an Airbus A320-214, registration OE-IJL, had occurred with the same operator just 14 days prior.
Findings
- The crew's selection of the incorrect takeoff position in the EFB was the primary cause of the error.
- The use of non-standard 'Positions' at Lisbon Airport caused confusion, as the software labels did not clearly correspond to specific taxiway names.
- The procedural safeguard of cross-checking EFB distances against the aerodrome ground chart failed to detect the discrepancy.
- Human limitations in perceiving subtle differences in acceleration rates made it difficult for the crew to recognize the reduced thrust setting during the takeoff roll.
Safety action
Following the incidents, the aircraft operator issued notices to flight crews to clarify takeoff positions and raise awareness of the risks. A NOTAM was also issued to highlight the confusing runway holding point naming. Additionally, the airport authority committed to renaming taxiways so that Taxiway S intersects the runway at only one point to prevent future confusion.