27 Dec 2016 - 737-800, VT-JBG (35083/2535), FF May 2008, operated by Jet Airways overran the runway 08 following a rejected take-off at Goa (VOGO) at 04:45L.
The final report states that the Captain (the F/O was PF) pressed TOGA when the thrust on no.1 engine was 40% and no.2 engine was 28% in deviation from SOP, which caused the No.1 engine thrust to increase at a faster rate than no.2 resulting in aircraft yawing towards right. In the absence of timely desired corrective actions including reject takeoff, the aircraft veered off the runway and continued to move in a semicircular arc on the undulated ground resulting in substantial damages to the aircraft.
The path on the ground during the event was due to the asymmetry in the thrust. The number one engine at full thrust and the number two engine at idle thrust. The number one thrust lever may have been moved forward inadvertently as the aircraft was travelling over a rough surface.
Boeing have since issued a reminder to operators in a Fleet Team Digest (737NG-FTD-02-18001) to pass on to their crews about the correct procedure for setting takeoff thrust. It follows 8 confirmed aborted takeoff events in 2017 resulting from advancing the throttles before engines were allowed to stabilize at 40% N1.
Goas only runway, 08/26 is 3458 x 45 meters.
VOGO 270000Z 06004KT 3000 BR NSC 21/20 Q1010 TEMPO 2000 BR
*** Updated 23 Nov 2020 ***
History of Flight
The F/O (723h TT, 472h on type) was PF. When aircraft was cleared for take-off, the crew completed the before take-off checklist and at 23:33:04 crew started pushing TLA to increase the thrust. As per the statement of crew, after taking TLA ahead of 40%, PIC pressed TOGA for takeoff. As soon as TOGA was pressed, the aircraft started drifting towards right. Within 10 to 12 seconds of pressing TOGA, the aircraft went into unpaved surface. As per the crew, they tried to apply brakes, rudder and use NWS to steer the aircraft, but due to heavy bumps could not apply control effectively. The aircraft went out of control and continued into unpaved surface. The aircraft stopped at a distance of 219 m from the runway edge and just short of periphery road. During this trail it had hit PAPI lights.
Damage to the aircraft
The aircraft suffered substantial damage during the accident. Some of the major damages are as follows:
Trajectory of VT-JBG
Take-off roll & the Accident
Runway heading for Goa runway 26 is 261. The reference take-off N1 is 95.7%. The aircraft heading on line-up was 256 and TOGA was pressed at 23:33:17. During the twelve second period from 23:33:05 to 23:33:17 both the thrust levers were advanced for take-off. The throttle resolver angle increased from idle thrust position which is 36/36and reached the position of 45/47. During this period the left brake pressure indicates 252psi and the right brake pressure 38psi.The rudder position is neutral. At time 23:33:17, the N1 parameters on both engines are not symmetrical. The fuel flow on both engines has a difference of 400lbs/hr. Fuel flow for number one engine is higher as the thrust produced by number one engine is higher. The application of thrust for takeoff is not as per the Jet Airways documented procedure for take-off which states that both thrust levers must be advanced till the N1 displayed is 40% and then TOGA must be pushed.
The asymmetry in the thrust setting prior to TOGA application caused the number one engine to increase thrust at a faster rate than the number 2 engine.
From time 23:33:17 to 23:33:34, as the thrust was increased there was an increase in heading from 257 to 270. There was left rudder application and constant left brake application. During this period at 23:33:20 the number 2 engine thrust increased but was lagging behind the number one engine by 46%. After a second, the number 2 engine thrust further increased but was lagging behind the number one engine by 47%. This was the maximum value in the difference of the N1 parameter between both the engines. 03 seconds later, the reference N1 was reached on number one engine and the number two engine was at 89%.
During this period it can also be seen that at 23:33:25, number 2 thrust lever is moved to the idle position. There is a continuous increase in heading and constant application of the left brake. The heading increases by 34 degrees in a period of 8 seconds. When the no. 2 thrust lever is moved to idle then there is decrease in EGT, fuel flow and N1. The values consistently reduce in the period of 8 seconds. The rudder had a fixed value indicating left deflection.
2 seconds later, auto-throttle is disconnected followed by an increase in right brake application. At 23:33:31, the aircraft has a ground speed of 47kts which was the maximum value of the ground speed during the accident. For 2 seconds at this point, there is an increase in application of brake pressure on both the brakes.
As can be seen the procedure for reject take-off was not as per the Boeing procedure for reject take-off.
At 23:33:34, there was an increase in the number one TLA by one degree and this caused the N1 to increase. There is an increase in the fuel and EGT of the number one engine. The number two engine thrust lever was at the idle position with reduction in fuel flow and EGT. The ground speed of the aircraft accordingly was reducing. The maximum value of left brake pressure recorded during the accident was 1915. The rudder position showed left deflection. Thereafter for two seconds the engine parameters of the number one engine increased though the ground speed of the aircraft reduced. At 23:33:37, there was an increase in the TLA of the number one engine by one degree and this caused the N1 to increase. The initiation of the reverse thrust for the number two engine began as there was change in the TLA. The ground speed of the aircraft continued to reduce. After 2 seconds, again there was an increase in the TLA of the number one engine by three degrees which further caused the N1 to increase. A second later TLA of the number one engine was further increased by one degree which caused the N1 to increase further. The N1 for number one engine reached 102% which was the maximum value recorded during the accident. During this period the number two engine reverse thrust sleeve was still getting deployed. EGT and fuel flow for the number two engine continued to reduce with reduction in the ground speed of the aircraft. At 23:33:43, both start levers were moved to cut-off position and the DFDR had also stopped recording.
The CVR recording was downloaded and heard by the Committee. During the line up the aircraft was aligned on a heading of 256. The visual cross-check was carried out by the captain as the centre line markings passed thru the aircraft nose. The PIC did not allow the engine to stabilize as documented in the standard operating procedures prior to pressing TOGA.TOGA was pressed with the number one engine at 40% and the number two engine at 28%. Correlating the above DFDR analysis with the CVR, the PIC had a very small time frame to decide to reject to take-off. During the period of 23:33:34 till 23:33:42 the CVR clearly indicates that the PIC was not effective in controlling the aircraft. Increase in the TLA of the number one engine during this period was probably due to the fact that the aircraft was travelling over a rough surface and the PIC though tried to close the thrust levers but inadvertently moved number one forward thereby increasing the N1 on the number one engine.
DFDR data also indicates that as the aircraft started turning to the right during the take-off procedure PIC tried to correct it with the application of left brake. This is indicated by continuous left brake application during the take-off roll. During the entire phase of flight the speed-brakes lever was in the down detent.
Probable cause of the Accident:
The PIC pressed TOGA when the thrust on no.1 engine was 40% and no.2 engine was 28% in deviation from SOP, which caused the No.1 engine thrust to increase at a faster rate than no.2 resulting in aircraft yawing towards right. In the absence of timely desired corrective actions including reject takeoff, the aircraft veered off the runway and continued to move in a semicircular arc on the undulated ground resulting in substantial damages to the aircraft.