Easyjet A320 at Lisbon on Sep 16th 2019, wrong performance calculation results in late takeoff
Last Update: August 7, 2020 / 14:45:52 GMT/Zulu time
The British AAIB reported Portugal's GPIAA delegated the investigation to the AAIB and released their final report concluding the probable cause of the serious incident were:
The aircraft took off using incorrect performance data for the intersection used. A selection error was made in the EFB calculation which led the crew to believe that they had calculated performance information for a departure from S1 when in fact they had selected the full length of the runway. In this case, as in the two previous identical incidents, the final barrier of checking the runway distance in the performance calculation against the aerodrome ground chart failed to prevent to error. Human performance limitations mean it is difficult for pilots to recognise and react to the performance error once the takeoff has begun, so robust adherence to procedures is a key defence against such incidents occurring.
The AAIB reported the takeoff distance available from U5 was 1395 meters less than the takeoff distance available full length of the runway. As result V1 for departure from U5 would have been 142 knots, not 162 knots as computed.
The AAIB analysed:
During pre-flight preparation, both flight crew of G-EZWE selected PSNSTMP in the EFB believing it to be where Taxiway S1 crossed Runway 21, but the position was actually for the full length of the runway. The operator’s SOPs required the crew to cross-check the distance shown in the EFB against that shown in the aerodrome ground chart for the takeoff position, but this cross-check did not capture the error. As a result, a lower power setting was used for takeoff than was required for the actual takeoff from Taxiway U5 intersection (Taxiway S1 intersection was more limiting). G-EZWE lifted off 110 m or, at the speed at which the aircraft was travelling, approximately 1.3 seconds before reaching the end of the runway. This was the third aircraft from the same operator, although one was operating under a different AOC, which had experienced similar incidents in the previous six months.
In all three cases the pilots were confused by the EFB intersection selections as they did not use the actual taxiway names. Also, there were two points on the runway which intersect Taxiway S (1 and 4) both of which might have been thought by the crew to be in the EFB as PSNSTMP as the taxiway numbers are not used in the nomenclature.
During the completion of the initial calculation the crew were interrupted numerous times despite the SOP mitigations that the operator had in place. The commander also had no access to the EFB once the aircraft taxied due to an inoperative cradle. He was not, therefore, in a position to see the taxi plate or the performance calculation, although he was not required to be by the company SOPs. The EFB battery condition had substantially deteriorated over time and the EFB was not useable for long without being charged by the cradle. The UK CAA decided to revise the EFB compliance checklist, SRG form 1849, to ensure that the requirement for a periodic battery replacement programme is emphasised.
The crew did not recognise the takeoff performance was incorrect until a late stage of the takeoff run. This would match with previous investigations completed by the AAIB which have shown that humans are not physiologically adapted to identify different acceleration rates, and often do not realise something is wrong until the end of the runway comes into view. As in previous incidents, TOGA thrust was not selected despite the compromised takeoff performance.
The magnitude of the error meant that had the aircraft stopped from a speed close to or at V1 , a significant overrun could have occurred. This could have caused significant damage to the aircraft and its occupants.
The AAIB reported following safety actions were taken:
Following the previous incidents, the AAIB reported that the Lisbon Airport operator intended to rename taxiways to remove the risk of confusion between the two points where Taxiway S crossed Runway 21. The taxiways would be renamed so that Taxiway S intersected the runway at only one point; S4 (full length). This safety action was completed, albeit after the incident to G-EZWE, and is reported here.
The operator has moved onto Flysmart L6 performance software which now shows the crew a pictorial image of the takeoff point used for the calculation.
The takeoff point selection menu was also amended to eliminated Position S making it clear to the crews that this was full length for Runway 21.
The UK CAA decided to revise the EFB compliance checklist, SRG form 1849, to ensure that the need for a periodic battery replacement programme is emphasised.
The AAIB released safety recommendation:
- Safety Recommendation 2020-003:
It is recommended that ANA Aeroportos de Portugal discontinue the use of takeoff Positions at Lisbon Airport to minimise confusion concerning takeoff points.
This article is published under license from Avherald.com. © of text by Avherald.com.
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