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. During pre-flight planning, the crew intended to calculate takeoff performance for a departure from the intersection of Runway 21 and Taxiway S1. However, while updating their calculations in the Electronic Flight Bag (EFB), the pilots selected a software entry labeled 'PSNSTMP'.
While the crew believed this entry corresponded to the S1 intersection, it actually represented the full length of the runway (the S4 intersection). Because the takeoff was actually performed from the U5 intersection, the available runway distance was 1,395 m less than what the crew had calculated. Consequently, the aircraft utilized a reduced engine thrust setting inappropriate for the actual runway length. During the takeoff roll, the commander noted that the acceleration "felt wrong," but the crew did not select TOGA thrust. The aircraft became airborne and passed the upwind runway threshold at a height of approximately 100 ft aal.
The investigation
The AAIB investigation, conducted on behalf of Portuguese authorities, examined flight data from the FDR and DAR, as well as the cockpit voice recorder. The investigation focused on the nomenclature used within the EFB software and the airport's ground charts.
Investigators found that the use of specific "Positions" at Lisbon Airport created significant ambiguity. The EFB software used temporary labels (PSNUTMP and PSNSTMP) due to a NOTAM regarding an obstacle. The investigation also identified that a second, identical incident involving an Airbus A320-214, registration OE-IJL, had occurred with the same operator just 14 days prior, where the aircraft also lifted off significantly before the runway threshold.
Findings
- The crew's selection of the 'PSNSTMP' entry in the EFB was the primary cause of the performance error, as it referred to the full runway length rather than the intended S1 intersection.
- The existing procedural requirement for pilots to cross-check EFB distances against aerodrome ground charts failed to detect the discrepancy.
- The naming convention for takeoff "Positions" at Lisbon Airport contributed to the confusion between different runway intersections.
- Human physiological limitations made it difficult for the crew to recognize the insufficient acceleration once the takeoff roll had commenced.
Safety action
Following the investigation, the following actions were recorded:
- The airport authority committed to renaming taxiways so that Taxiway S intersects the runway at only one point.
- The aircraft operator issued notices to flight crews to clarify takeoff positions and raise awareness of the risks associated with incorrect intersection data.
- A NOTAM was issued to alert pilots to the confusing naming of runway holding points.