Incident Overview
On 29 April 2011, an Airbus A321-211, registration G-NIKO, operated a scheduled commercial passenger flight from Manchester Airport to Heraklion, Crete. The aircraft had two CFM56-5B3/P turbofan engines, was manufactured in 2000, and carried 8 crew and 223 passengers. No injuries were reported, and there was no damage to the aircraft.
Sequence of Events
The flight crew reported at 0720 hrs for the two-sector duty. The commander, aged 45 with 13,050 total flying hours (2,255 on type), was the pilot flying (PF) for the first sector. The loadsheet was generated at 0837 hrs, 17 minutes after the scheduled departure time of 0820 hrs. The commander accepted it from the dispatcher and checked it. While doing so, the co-pilot asked for the takeoff weight to begin performance calculations. The commander read out what he thought was the Actual Take Off Mass (ATOM) but mistakenly said the Zero Fuel Mass (ZFM) of 69,638 kg. He wrote that figure in the ATOM space on the navigation log. The Standard Operating Procedure (SOP) required him to compare the Estimated Take Off Mass (ETOM) with the ATOM, but he instead compared his written figure (69,638) with the Estimated Zero Fuel Mass (EZFM) on the line below.
The commander then entered data into the Flight Management System (FMS), including the ZFM in the INIT B page (a mandatory entry). The loadsheet was passed to the co-pilot who checked and confirmed it matched the commander's FMS entry. The commander used the incorrectly written figure (69,638 kg) for takeoff calculation. The SOP required each pilot to perform separate takeoff performance calculations on a laptop computer, then compare results and enter takeoff data (speeds, flex thrust, configuration, trim) into the FMS. The laptop calculated speeds based on the erroneous mass: V1=131 kt, VR=134 kt, V2=135 kt, with Flap 2, Flex 57°C, and green dot speed 214 kt. (Correct figures for an ATOM of 86,527 kg would have been: V1=155 kt, VR=155 kt, V2=156 kt, Flap 2, Flex 39°C, green dot 240 kt.) The crew crosschecked laptop figures between themselves but missed the crosscheck with the FMS green dot speed.
Before departure, a Last Minute Change added one male passenger plus bag (+89 kg), which did not require a takeoff performance recalculation.
Takeoff and Climb
The aircraft took off from Runway 05L (TODA 3,245 m). During rotation, the commander noticed the sidestick felt heavier than expected. After lift-off, he observed the Lowest Selectable Speed (VLS) indication moving "too far" up the speed scale on his Primary Flight Display. He reduced the pitch attitude and covered the thrust levers in case more power was needed. The aircraft accelerated and climbed, but at a slower than normal rate. In the cruise, the crew checked performance figures and realized they had used ZFM instead of ATOM.
Discussion
The aircraft took off with less thrust and lower reference speeds than required. The effect of attempted rotation at too slow a speed was noticeable to the PF through aircraft feel and speed scale displays. He responded by reducing pitch, allowing acceleration to a safe climb speed. The ATOM was approximately 17,000 kg heavier than the figure used, significantly affecting thrust and speed computations. The first error was the misreading of ZFM instead of TOM by the commander. Later, several missed opportunities to detect the error through SOPs occurred, including the missed crosscheck of laptop green dot speed against the FMS-calculated value. The operator subsequently issued a Flight Safety Bulletin to flight crews and made changes to the navigation log layout and SOPs concerning the green dot crosscheck.
Other Events
The AAIB Bulletin noted that there have been a significant number of reported incidents and several accidents worldwide resulting from errors in takeoff performance calculations. Studies include the ATSB report 'Take-off Performance Calculation and Entry Errors: A Global Perspective' and the BEA Safety Study 'Use of Erroneous Parameters at Takeoff'. The AAIB had previously made Safety Recommendations (2009-080 and 2009-081) concerning takeoff performance monitoring systems, which were under consideration by the European Aviation Safety Agency at the time.