
Darwin Airport Ground Chart at time of the incident
On 12 June 2011 a flight-crew were preparing an A321-231 – registered - for a scheduled passenger flight from Darwin, Australia to Bali, Indonesia.
The load-sheet provided the flight-crew with a planned TOW which was approximately 10 tonnes below MTOW. Accordingly, the flight-crew were able to plan for an intersection departure from runway 11, via intersection with taxiway Bravo, in accordance with the operators SOPs. This provided a TODA of 2316m. The flight-crew also elected to use a flex-thrust (reduced thrust) setting for the take-off, as standard procedure that reduces internal engine temperatures, increasing the engine-lifespan.
The Captain (PIC) acting as PNF for the sector prepared the final TOW calculation, and made performance calculations using the Aircraft Performance Manual. He then left the aircraft to complete the pre-flight external aircraft inspection. Whilst outside, the First Officer, PF for the sector, cross-checked the final TOW and performance calculations made by the PNF. During this cross-check PNF detected an error in the calculations made by PF.
Subsequently PNF corrected the error, and recalculated new performance calculations, including critical V speeds for the departure. Unfortunately the ‘corrected’ calculations were correct figures but applied to the wrong performance table. PF had used a chart for a full length departure, as TODA od 3444m as opposed to the intersection departure as planned. A difference of 1128m from the Brave intersection departure point.
On return to the flight-deck, PF advised PNF of the original error and his actions to rectify it.
PNF then cross-checked the amended calculations prepared by PF, receiving the Aircraft Performance Manual from PNF with a card inserted into the manual to
bookmark the performance chart he’d used. PF checked the revised data on the page presented, but failed to notice the error of page selection by PNF.
The crew completed then pre – flight preparations and taxied for runway 11 via taxiway Bravo.
On departure it became apparent to PF passing 120-130 knots that there was insufficient distance left to complete a Rejected Takeoff, even though the (incorrectly) calculated V1 was higher. He accordingly decided not to reject if conditions suggested he should beyond that point.
The aircraft rotated at the (incorrectly) calculated VR with approximately 450m remaining. The flight-crew kept the flex-thrust setting for departure, not electing to selected TOGA. Later in the flight, the flight-crew reflected on the situation and recalculated the performance figures, discovering the error in their planning.

THE FACTS
Planned TODA: 3444m V Actual TODA: 2316m
Planned V1: Approx 160 KIAS V Actual V1: 138 KIAS
If the crew had rejected at erroneously calculated V1 of 160KIAS the aircraft would have required an additional 1000m of runway for the required accelerate and stop distances required. If an engine failure occurred at the calculated V1 the obstacle clearance would have been compromised.
What was the error?
The first error was a slip committed by PF in miscalculating the final TOW was well identified by PNF independently cross checking the calculation.
However PNF then used the wrong performance table, creating the second error, an additional slip as intended action was not completed correctly.
The third error, either a slip (not identifying the use of the wrong performance chart during his independent cross-check) or a lapse (forgetting to check the performance chart in use), was made by PF not identifying the error made by PNF.
It had become common practice for many line-pilots to ‘bookmark’ the Aircraft Performance tables for calculations. This involved the pilot completing the performance calculations handing the performance table book to the other pilot, with the relevant performance table marked for their attention.
This relatively simple and at face value, innocent action is flawed. By presenting the ‘cross-checking’ pilot with the ‘right’ performance table to use, they are statistically less likely to check that the presented performance table is actually the correct table to be used for the circumstance.
By passing the book to the cross-checking pilot closed, they must analyse which performance table to use independently. This reduces the risk of both pilots using an incorrect data set for making their performance calculations.
Following the incident the operator changed its SOPs to specifically prohibit the book marking culture, ensuring that independent calculations were made for a cross comparison between flight-crew members.
The Airbus operator used a paper based performance data table book for runway performance calculations. This tried and tested method has been used in the industry for decades. A performance table is provided for each airport the operator flies to, with various tables for different runways and intersection departures.
Many airlines now utilise the Airbus led Less Paperwork Cockpit (LPC) philosophy and use electronic devices (laptops or tablets) with custom performance and mass and balance software to calculate performance data.
Although this software is designed carefully to reduce human error entry input to a maximum, the risk cannot be wholly eliminated while humans are still in the loop.
The “bookmark factor” – whereby the other pilot is passed the performance table book with a marked page, implying the page has been identified and selected as the correct one by the pilot passing it – is removed from the equation, the pilot entering the data can still select the wrong start of takeoff run in the software.
Ultimately paper or paperless performance is an infallible design which requires particular care of this involved in calculating figures. While humans are in the loop, human error risk will exist requiring mitigating behaviour and actions to minimise the risks of incorrect data being used.
Learning Points:
- Don’t ‘bookmark’ documents for colleagues. Doing so increases the probability of confirmation bias, and reduces the probability of effective independent cross-checking.
- Take care to really check all data prior to using it. Pages, charts, dates, intersections, temperatures, pressure settings etc. Don’t assume your colleague is correct.