On 21 April 2017, a Boeing 777-300 (VT-JEW) being operated by Jet Airways on a scheduled international passenger flight from Amsterdam to Toronto as 9W234 had just taken off from runway 18C in day VMC when it became evident that a tail strike may have occurred. After fuel dumping and return, this was confirmed although the runway contact was not sufficient to compromise the structural integrity of the aircraft.
A Serious Incident Investigation was carried out by the Dutch Safety Board making use of relevant data from the CVR and the FDR. The experience or duty period of the operating crew was not recorded nor was the presence or absence of any observing supernumerary crew on the flight deck.
Shortly before departure from the gate, the Captain was advised of one “no show” passenger which had necessitated a handwritten adjustment to the weights shown on the load sheet and it was presented for acceptance and signature. The weights for takeoff were then entered into each pilot’s EFB.Then, after notification of departure runway and SID, both pilots adjusted the information in their EFBs and crosschecked the output of their independently calculated EFB outputs - the flap setting, engine thrust (with assumed temperature if thrust reduced) and takeoff V speeds. After this, the First Officer entered the data from his EFB into the FMS and “the ZFW [Zero Fuel Weight] weight from the load sheet was used to program the FMS”. The FMS V speeds were then replaced by those calculated by the EFBs and this change was checked on the FMS takeoff reference page.
With the Captain acting as PF, the aircraft then taxied as cleared to runway 18C. Once cleared to takeoff, the Captain set the EFB-calculated takeoff thrust and the First Officer monitored the speed and on reaching the V speeds announced them. On the VR call, rotation to the indicated pitch attitude was commenced and the aircraft became airborne. The Captain stated that he had found the handling in pitch “sloppy” and that the aircraft had not accelerated and behaved as he had expected, which had led him to limit the pitch attitude achieved during rotation to less than the PFD command bar indicated. The First Officer recollected that “during or just after the rotation, he felt a slight pitch hesitation and a bump” but this had not been accompanied by any noise. However, the aircraft became airborne well before the end of the 3,300 metre long runway.
A few minutes after checking in with the Departure frequency, the controller advised that TWR suspected that a tail strike may have occurred and two minutes after that one of the cabin crew advised that “an unusual scraping sound had been heard during the takeoff”. The crew then asked for and received clearance to stop their climb at FL150. Although the EICAS did not indicate that a tail strike had occurred, it was decided to make a precautionary return which, after fuel dumping, was accomplished uneventfully to a landing on runway 27.
An inspection after arrival on the assigned parking gate found that although the tail skid detection system shoe had been “slightly scraped” during a tail strike, it had remained within AMM limits for despatch. The absence of a ‘TAIL STRIKE’ warning on the flight deck was attributed to that fact that the “fin” of the tail strike detection system was still intact.
Why It Happened
The tail strike occurred when the aircraft was rotated at a speed lower than the actual takeoff weight of the aircraft required because the takeoff weight used to calculate the takeoff performance figures was 70 tonnes less than the actual weight. This had resulted in the insufficient thrust to accelerate the aircraft at the necessary rate and the setting of V speeds which were much lower than those actually required for the prevailing weight. Since the absence of sufficient thrust during what was a reduced thrust takeoff was not detected by the crew during takeoff, thrust was not increased in response to perceived abnormally slow acceleration.
The origin of the incorrect takeoff weight was the ‘Last Minute Change’ (LMC) made to the automatically generated load and trim sheet when one of the 344 checked-in passengers did not board the aircraft. Whilst the actual adjustment required for this circumstance was of marginal significance to computation of the takeoff performance data - a reduction of 100 kg - the load controller’s handwritten LMC introduced a significant error in the takeoff weight by writing it clearly but erroneously as 229,075 kg instead of 299,075 kg - although the original figure was still clearly visible as shown on the illustration below. As the same error was not made with the correction to the landing weight, this then showed a landing weight which was higher than the takeoff weight. It was noted that the load controller involved had “ten years of experience in handling flights for the airlines including the one concerned”.
The part of the load sheet where the error was made. [Reproduced from the Official Report]
Whilst this carelessness of the load controller involved was the source of the problem encountered, it was evident in signing for their acceptance of the hand-amended load and trim sheet, the Captain could not have reviewed the handwritten changes with necessary care to check that only the necessary 100kg had been deducted from all three weights. He had also not noticed that the zero fuel weight was only an implausible 4 tonnes less than the takeoff weight and that the landing weight shown was more than the takeoff weight.
Crucially, in order for both pilots to enter the ZFW and TOW into the pilots individual EFBs, the Captain was found to have merely read out the amended weights from the load sheet as both he and the First Officer simultaneously entered them into their EFBs. The First Officer was not able to check the load sheet himself before entering the weights on it although both pilots could reasonably have been expected to notice when entering the ZFW and TOW into their EFBs that the difference between them of only 4 tonnes was nowhere near the 60 tonnes they were expecting to burn whilst crossing the Atlantic.
The effect of the use of significantly incorrect performance data on takeoff safety margins was found to have been compromised. It was calculated that without use of thrust reversers, an all-engines operative rejected takeoff at V1 would have resulted in an overrun but had maximum reverse thrust been used, an overrun would have been avoided by 52 metres. It was also calculated that had an engine failure occurred during the first segment of climb (from V1 though lift off to landing gear retracted), the thrust on the remaining engine would have been unable to provide a positive climb gradient. An engine failure between gear retracted and 400 feet agl with reduced thrust on the remaining engine would have resulted in a climb gradient that was less than 1%. The specified minimum climb gradient for the SID being flown was 3.3%.
It was noted that at the time the Investigation was complete, there was no on board system on the 777-300 which would generate a warning if the commanded engine thrust setting not sufficient for the aircraft configuration and runway/weather conditions.
The Conclusions of the Investigation included the following:
- The use of incorrect data for the takeoff performance calculation led to an incorrect thrust setting resulting in a takeoff being performed without the required safety margins. In case of an engine failure at or just after the V1 decision speed or at or after liftoff, the aeroplane would not have been able to continue the flight safely.
- Investigation reports into takeoff performance occurrences show that in the past decades the airline industry has made efforts on a global scale to improve the operational procedures to prevent incorrect takeoff thrust settings. However these efforts have not resulted in a significant reduction of the risk and incidents.
- Introduction of new systems that are fully integrated in the cockpit and, among others, provide a timely alert to flight crew when the achieved takeoff performance is inadequate for the given aeroplane configuration, actual weight and balance and aerodrome conditions, is a matter of urgency.
Four Safety Recommendations were made as a result of the findings of the Investigation as follows:
- that the European Union Aviation Safety Agency (EASA) and the Federal Aviation Administration take the initiative in the development of specifications for and, subsequently, development of requirements for an independent on board system that detects gross input errors in the process of takeoff performance calculations and/or alerts the flight crew during takeoff of abnormal low accelerations for the actual aeroplane configuration as well as insufficient runway length available in case of intersection takeoffs and do so in close consultation with the aviation industry, including manufacturers of commercial jet transport aircraft.
- that the International Air Transport Association (IATA) develop a standard policy for airlines with regard to procedures for reduced thrust takeoffs, including a risk analysis addressing cost reductions versus introduced safety risks.
- that Boeing research and develop for existing and future aeroplanes an independent on board system that detects gross input errors in the process of takeoff performance calculations and/or alerts the flight crew during takeoff of abnormal low accelerations for the actual aeroplane configuration as well as insufficient runway length available in case of intersection takeoffs.
- that the International Civil Aviation Organisation (ICAO) note the conclusions of this report and introduce provisions addressing an independent on board system that detects gross input errors in the process of takeoff performance calculations and/or alerts the flight crew during takeoff of abnormal low accelerations for the actual aeroplane configuration as well as insufficient runway length available in case of intersection takeoffs.
The Final Report was published on 15 October 2020.