Jet Airways B773 at Amsterdam on Apr 21st 2017, tailstrike on departure
Last Update: October 15, 2020 / 13:43:10 GMT/Zulu time
Ground observers reported no damage was visible on the aircraft.
The Dutch Onderzoeksraad (DSB) reported they dispatched investigators for exploratory research of an incident during takeoff at Schiphol Airport.
The airline reported the aircraft suffered a suspected tail scrape during departure and returned to Amsterdam. The aircraft is currently being examined by maintenance engineers.
A passenger reported that no evidence of a tail strike was discovered, however, the passengers were kept on board for 6 hours and became very impatient, then the flight was postponed to the next day and the passengers were taken to hotels.
The occurrence aircraft is still on the ground in Amsterdam 12 hours after departure.
On Aug 15th 2017 the DSB reported in their quarterly bulletin that the aircraft did suffer a tail strike during rotation from runway 18C. The crew dumped fuel to reduce the aircraft weight to maximum landing weight and landed back. The occurrence was rated a serious incident and is being investigated.
On Oct 15th 2020 the DSB released their final report concluding the probable cause of the serious incident was:
The tailstrike was caused by an overrotation of the aeroplane during the takeoff, which was the result of a lower than required rotation speed. The reason for this was that the actual takeoff weight was higher than the takeoff weight that had been used for the takeoff performance calculation.
As a consequence, the take off took place with insufficient engine thrust, which was not detected by the crew and not corrected by manually advancing the thrust levers to provide the additional thrust needed.
One passenger had not shown up, which resulted in a manual last minute change on the loadsheet. The actual takeoff weight on the loadsheet was amended and written down erroneously. This was not detected and the data was used for the takeoff performance calculation. It could not be determined if a warning was generated by the Electronic Flight Bag, resulting from the difference between the erroneous takeoff weight manually entered and the correct weight calculated by the Flight Management System.
Under time pressure, incorrect data was supplied to the pilots. Neither the airline’s loading procedures nor the cross check of data by the pilots did prevent the use of the wrong data for the takeoff performance calculaton.
The interaction between human performance, the cross check of data by the pilots, the airline’s loading procedures, limited systems integration and operational pressure to meet the planned takeoff time contributed to the erroneous takeoff performance calculation.
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.
It is urgent to introduce 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.
The DSB reported there were no injuries and no damage to the aircraft.
The DSB introduced the investigation:
On 21 April 2017, a Boeing 777 took off from Amsterdam Airport Schiphol in the Netherlands. During the initial climb, the flight crew was informed by Air Traffic Control that probably a tail strike had occurred. The crew decided to treat the event as an actual tail strike and returned to Schiphol. After landing, it appeared that a tail strike had occurred, but that the wear of the tail skid shoe was within limits and no immediate repair was necessary.
At an early stage of the investigation, it was found that an incorrect weight had been entered in the Electronic Flight Bag and that insufficiently applied takeoff power (referred to as thrust setting) probably had caused the tail strike. The Dutch Safety Board (DSB) investigated similar occurrences of insufficient thrust settings in the past and recommended European Union Aviation Safety Agency (EASA) in 2018 among others to start the development of specifications and the establishment of requirements for an autonomous Takeoff Performance Monitoring System.
The DSB summarized the flight preparation leading to the error of 70,000kg for the no-show passenger:
The load controller received the final baggage and cargo weights and then sent those figures to the CLCU. The load controller asked the CLCU to provide a loadsheet on the presumption that all planned passengers had boarded. When the final loadsheet from the CLCU was received, it was discovered that one passenger had not shown up at the gate. As a result, as there was little time, the load controller made a last minute change (LMC). The load controller reduced the actual weights10 by 100 kg11 and listed the new values manually on the loadsheet. For the actual takeoff weight the load controller wrote down 229,075 kg instead of 299,075 kg, a difference of 70,000 kg.
The crew entered the load sheet data into the flight management system, de-selected the automatic reference speeds and entered the reference speeds computed based on the load sheet.
The DSB then summarized the sequence of events:
After starting the engines, pushback and completing the taxi out checklist, the aeroplane started taxiing. The aeroplane proceeded to the beginning of runway 18C. Prior to the line-up on runway 18C, the crew switched off the air conditioning packs according to their ‘packs-off’ takeoff procedure. Subsequently the crew received the takeoff clearance from Air Traffic Control (ATC).
The captain, who was pilot flying, set the takeoff thrust, as calculated by the EFB. During the takeoff roll, the first officer, who was pilot monitoring, observed the captain’s actions, checked the instruments and called out the takeoff reference speeds. When the first officer made the Vr call, the captain applied back pressure on the control column and aimed to follow the flight director pitch commands14 on his Primary Flight Display to obtain the required climb attitude.
The first officer stated that during or just after the rotation, he felt a slight pitch hesitation and a bump. These occurred without any noise and/or caution alerts being generated. The captain stated that the aeroplane was ‘sloppy’ on the fight controls [sic!] and not behaving and accelerating as expected. Because of this, the captain limited the pitch to just below the flight director pitch bar. He did not select additional thrust.
Shortly after becoming airborne, the crew contacted Schiphol Departure. After approximately 4 minutes, the departure controller informed the crew that a possible tail strike had been observed by an air traffic controller in the tower. The flight was instructed to climb to flight level16 (FL) 240. Approximately 6 minutes after the takeoff, a cabin attendant notified the flight crew that an unusual scraping sound had been observed during the takeoff. The flight crew requested a clearance from ATC to stop the climb at FL150. This clearance was provided by ATC.
The flight crew analysed the situation and the first officer stated that he had not noticed any unusual sounds, but had felt a slight pitch hesitation and bump during or just after the rotation. No ‘TAIL STRIKE’ caution was generated by the Engine-Indicating and Crew-Alerting System (EICAS). The flight crew, nevertheless, treated the event as an actual tail strike and initiated a return to Schiphol.
The flight crew performed the Tail strike checklist and informed ATC about their intention to return to Schiphol. Due to the fact that the actual aeroplane weight (as shown on the FMC17) was above the maximum landing weight, the crew decided to dump fuel to meet landing weight requirements. After the fuel jettison procedure had been completed, ATC provided radar vectors for a landing on runway 27. The aeroplane landed safely and taxied to a parking stand.
The DSB analysed:
The flight crew stated they experienced time pressure during the pre-flight process. It was felt that no time was available to pre-enter the estimated aeroplane weights from the preliminary loadsheet in the EFB and in the FMS.
The captain was distracted several times in his flight preparation flow. He stated that he was experiencing pressure and reached his saturation level. This created a situation in which the flight preparation process and the coordination between both pilots became less effective and vulnerable to error. The difference of 70,000 kg between the actual TOW and the TOW after the LMC correction can be considered as a large deviation. The perceived time pressure may have played a role in not detecting the erroneous takeoff weight on the loadsheet.
Entering the EFB calculated takeoff reference speeds into the FMS, a difference of 10 to 12 knots with the (correct) calculated takeoff reference speeds from the FMS existed. Normally the takeoff reference speeds between the EFB and FMS do not differ more than a few knots.
Adhering to standard operating procedures, cockpit flows and checklists enables flight crews to perform under high workload. As mentioned above, the flight crew was working under time pressure. The airline had an operating procedure to program the EFB and FMS. According to this procedure (FCOM Before Start Procedure), the captain has to read out loud the relevant information while the first officer programs and checks his EFB and the FMS.
In this instance, the captain read the erroneous takeoff weight and the first officer entered this incorrect number in the EFB and crosschecked it with the FMS. The first officer did not notice the difference between the stated takeoff weight of 229,075 kg by the captain and the gross takeoff weight of 299,400 kg (according flight data monitoring data) displayed by the FMS. The captain did not notice this difference either. The difference between the takeoff reference speeds, as displayed by the EFB and the FMS, was also not detected by both pilots.
In the Boeing manuals is clearly stated that the takeoff performance calculation shall be made by both pilots, independently from each other, whereafter the results shall be compared to detect gross errors. In this case the captain mentioned aloud to the first officer the takeoff weight to be used. The first officer used this weight to calculate the performance data on his EFB. By telling the first officer what weight to use, the takeoff performance calculation can no longer be classified as an independent process. The safety net to avoid gross calculation errors was therefore lost.
The takeoff performance calculation resulted in an engine thrust setting which was insufficient for the aeroplane’s actual weight.29 As a result, the aeroplane rotated at a speed below the speed needed for the actual weight. This resulted in the tail strike due to overrotation of the aeroplane due to the increased time from the beginning of the rotation to the actual liftoff of the aeroplane.
The Boeing procedures specify that if a tail strike occurs, without a ‘tail strike’ caution message being presented on the EICAS, the flight could be continued. However, these procedures had not been incorporated in the airline’s procedures. Based on the unusual scraping sound that had been observed by a cabin attendant, the first officer who experienced a bump and an air traffic controller who had observed a possible tail strike, the flight crew treated the event as an actual tail strike. They followed airline’s procedures and thus returned to Schiphol.
Analysis of flight data reveals that during rotation, the column deflection increased while the elevator deflection decreased, which indicates that the tail strike protection system was active. It is however possible that the steering commands are increased beyond the capability for the tailstrike protection system to avoid a tailstrike. The DFDR revealed that the tailstrike protection system operated as designed with its maximum input to avoid a tailstrike.
Boeing made takeoff performance calculations to reveal the consequences of a potentially rejected takeoff with all engines operative and in case of a continued takeoff with an engine failure.
A rejected takeoff at V1 with all engines operative
For an all-engine operative rejected takeoff at a V1 of 152 knots, with the actual thrust and flap setting and no thrust reversers being used, the stopping distance was 10,798 ft. The Accelerate Stop Distance Available (ASDA) for the runway used is 10,732 ft. The actual stopping distance of 10,798 ft would have exceeded the ASDA and a runway overrun would have occurred. For the maximum reverse thrust case, using ASDA, the aeroplane would have remained within the confines of the runway by 169 feet.
A continued takeoff with an engine failure at or just after V1
If an engine would have failed during or before the first segment of climb31, reduced thrust on the remaining engine would have resulted in a negative climb gradient. If an engine failed during the second segment of climb32, reduced thrust on the remaining engine would have resulted in a climb gradient that was less than 1%. The reason for not being able to maintain the minimum climb gradient is that the actual airspeed flown was below the required minimum airspeed for a climb out with one engine failed. If the takeoff would have been continued with an engine failure at or just after V1, the minimum climb gradient of 3.3% for the standard instrument departure at Schiphol would not have been met.
This article is published under license from Avherald.com. © of text by Avherald.com.
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