During pre-flight preparations at Lisbon Airport Portugal, pilots of the Airbus A320-214 completed a takeoff performance calculation for a takeoff from Taxiway U5. During subsequent re-planning, the crew calculated performance using the full length of the runway, giving an additional 1,395 m of runway for the calculation. The aircraft took off from U5 but with lower thrust than was required because the calculation had assumed there was 1,395 m more runway available than was the case from U5. The aircraft passed the upwind end of the runway at 100 ft aal. The operator had another identical event 14 days later.
In both cases, the procedural barrier of cross-checking the runway distance against the aerodrome ground chart failed to prevent error.
Following this event, the operator acted to raise awareness of the issue with its crews and engaged with the aircraft manufacturer to review possible technical developments which might prevent a recurrence of these type of events. One Safety Recommendation is made to mitigate the risk of further confusion relating to take-off positions.