On 29 April 2011, an Airbus A321-200 being operated by Thomas Cook Airlines on a passenger service from Manchester UK to Iraklion, Greece took off in day Visual Meteorological Conditions (VMC) but failed to establish a climb at the expected speed until the aircraft pitch attitude was reduced below that prescribed for the aircraft weight which had been entered into the Flight Management System. No abnormal manoeuvres occurred and none of the 231 occupants were injured.
An Investigation was carried out by the UK AAIB. It was noted that the operating crew were cross qualified on both the Airbus A320 and the Airbus A321 but had more frequently flown the smaller A320. It was reported that the aircraft commander acting as PF had considered the side stick control had felt heavy as he rotated the aircraft for take off from runway 05L at Manchester and, after lift off, he had noticed the Lowest Selectable Speed (VLS) indication on his Primary Flight Display (PFD) speed-scale increasing. He had reduced the aircraft pitch attitude and takeoff climb was continued, although at less than the expected rate since no additional thrust was added. When the aircraft reached cruise level, the flight crew checked the performance figures which had been used and realised that Zero Fuel Mass (ZFM) had been used in place of Takeoff Mass (TOM) for the takeoff performance calculations and, as a consequence, the FMS had been programmed with speeds which were too low -
The comparison (correct figures in brackets) was:
Actual Takeoff Mass (ATOM) in tonnes: 69.6 (88.5)
V1 (knots): 131 (155)
Rotation Speed (Vr) (knots): 134 (155)
V2 (knots): 135 (156)
Flex 2 temperature (°C): 57 (39)
Green Dot Speed (knots): 214 (240)
It was noted that the flight was behind schedule. The initial source of the error was found to have been when the loadsheet was presented to the aircraft commander for acceptance and he inadvertently told the First Officer that the Zero Fuel Weight (ZFW) of 69.6 tonnes was the ATOM needed for the take off performance calculations. SOPs then required him to compare the ETOM, on the line above, with the ATOM as a cross check, but he had actually compared the figure he had written down as the ATOM (69,6 tonnes) with the EZFM on the line beneath. Subsequent SOP actions, including those which required each pilot to carry out a take off performance calculation separately, failed to alert either pilot to the effect of the original error.
It was clear that the aircraft had taken off using significantly less thrust and lower reference speeds than were required for the actual take off mass which was 17 tonnes heavier than had been used as a basis for the take off performance calculations. It was noted that take off with a premature rotation “has the potential to cause a tailstrike and a takeoff with inadequate thrust and speed could lead to a loss of control of the aircraft”.
Safety Action by Thomas Cook Airlines to amend the layout of the navigation log and to modify the SOPs for the crosscheck of the green dot speed (the speed corresponding to the best lift to drag ratio when clean) was noted.
More generally, it was observed that in recent years there had been a number of similar events attributable to errors in takeoff performance calculations and that “there must also have been many similar events which were either unreported and/or unnoticed, some of which will have had the potential to cause accidents”. It was further observed that the overall conclusions are that these events occur irrespective of the airline or aircraft type and that the errors are attributable to various different origins. It was noted that the fact that “there is no single solution to ensure that such errors are always prevented or captured” had led in the past to the suggestion of a Takeoff Performance Monitoring System (TPMS) operating by detection of aircraft acceleration and generating an alert if a takeoff was not progressing as expected.
The Investigating Agency was noted as having made two Safety Recommendations to European Aviation Safety Agency (EASA) in respect of the development of a specification such takeoff performance monitoring systems and the mandating of their use in their Final Report on a serious incident involving an Airbus A330 operated by the same airline in 2008 - A332, Montego Bay Jamaica, 2008 where the input of a weight lower than the actual one nearly led to a runway excursion.
The Final Report of the Investigation: AAIB Bulletin: 12/2011 EW/G2011/04/29 was published on 8 December 2011. No new Safety Recommendations were made but the two previous Safety Recommendations noted above and made to EASA in 2009 were restated in full with the remark that EASA “has not yet accepted these Safety Recommendations but they are under consideration”.
Similar A & I events on SKYbrary