It helped to have been taking off on a 14,000 feet long runway. Here is some additional albeit better information coming from Avherald...
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The South African Civil Aviation Authority (SACAA) have released their final report concluding the probable cause of the serious incident was:
Loss of a significant amount of lift on rotation during the takeoff caused by the automatic LE flap retraction logic retracting the Group ‘A’ LE flaps on receipt of spurious thrust reverser unlock signals from the no. 2 and no. 3 engines. The possibility of such an occurrence had not been identified during amendment of the retraction logic.
The SACAA wrote as last of their findings:
"The flying crew should be commended for the professional way that they controlled the aircraft during a critical stage during takeoff and thereby ensured the safety of the 283 occupants on board the aircraft."
The airplane was departing Johanneburg's runway 03L. The departure was planned at reduced takeoff power, the first officer was pilot flying. Calculated speeds were V1=150, Vr=168 and V2=176 KIAS at flaps 20. The #3 thrust reverser amber message displayed on the EICAS screen at about 125.6 knots (below V1), the #2 thrust reverser amber message at 159.9 knots (above V1, just below Vr). At this stage the leading edge Group A flaps retracted automatically according to system logic, speed was 164 KIAS. The airplane rotated at 173 KIAS and became airborne at 176 KIAS. The stick shaker immediately activatated at a radio altitude of 4 feet intermittently for 8 seconds during the next 15 seconds, significant buffeting was observed. The pilot flying, having significant experience with aircraft buffeting due to aerobatics flying, continued to fly the aircraft with the captain, remaining pilot monitoring, calling out aircraft height. The landing gear was retracted at 177 KIAS and the leading edge flaps immediately deployed again reaching their normal position at a height of 56 feet AGL, the stick shaker ceased at 186 KIAS. The leading edge flaps reached their deployed position again 23 seconds after retracting, the airplane performance returned to normal thereafter and the airplane climbed out. Whilst climbing through 7000 feet the crew declared PAN reporting problems with the #2 and #3 engine and decided to return to Johannesburg. The airplane continued to climb to FL150, dumped fuel and landed safely 92 minutes after liftoff.
The leading edge Group A flaps (all leading edge flaps inboard of the outboard engines) are designed to automatically retract if the airplane is in ground mode and either reversers #1 and #4 or reversers #2 and #3 are unlocked. This design is meant to reduce wear on the flap panels, that the airflow from the thrust reversers would produce on the extended panels.
The thrust reversers did not unlock and remained in their stowed position all time, however were at the rear end of their permitted travel in high power engine operation. The stow sensors for thrust reversers #1, #2 and #3 were rigged outside the requirements with the target set too far forward thus causing the unlocked indication with the thrust reverser cowls in their permitted yet rear position.
The crew were and remained unaware of the Group A leading edges having retracted due to this automatic retraction only visible on a separate indication. Only the extended flap EICAS display would have provided them with the according information, however the display was not brought up. The only available indication was a color change of the flap display in the regular EICAS display which however is hardly visible.
The SACAA noted in their findings: "During this time the flight deck crew had no indication or understanding of what had caused the lack in performance of the aircraft."
Several safety actions are underway as result of the occurrence. Boeing plans to change the system logic withdrawing the reverser unlock signal from the autoretract logic, which would continue to function based on the reverser handles and air/ground logic. This was put into an Airworthiness Directive by the FAA.
The SACAA released a number of safety recommendations concerning the man/machine interface, spurious alerts and robustness of software and hardware control logic.
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The South African Civil Aviation Authority (SACAA) have released their final report concluding the probable cause of the serious incident was:
Loss of a significant amount of lift on rotation during the takeoff caused by the automatic LE flap retraction logic retracting the Group ‘A’ LE flaps on receipt of spurious thrust reverser unlock signals from the no. 2 and no. 3 engines. The possibility of such an occurrence had not been identified during amendment of the retraction logic.
The SACAA wrote as last of their findings:
"The flying crew should be commended for the professional way that they controlled the aircraft during a critical stage during takeoff and thereby ensured the safety of the 283 occupants on board the aircraft."
The airplane was departing Johanneburg's runway 03L. The departure was planned at reduced takeoff power, the first officer was pilot flying. Calculated speeds were V1=150, Vr=168 and V2=176 KIAS at flaps 20. The #3 thrust reverser amber message displayed on the EICAS screen at about 125.6 knots (below V1), the #2 thrust reverser amber message at 159.9 knots (above V1, just below Vr). At this stage the leading edge Group A flaps retracted automatically according to system logic, speed was 164 KIAS. The airplane rotated at 173 KIAS and became airborne at 176 KIAS. The stick shaker immediately activatated at a radio altitude of 4 feet intermittently for 8 seconds during the next 15 seconds, significant buffeting was observed. The pilot flying, having significant experience with aircraft buffeting due to aerobatics flying, continued to fly the aircraft with the captain, remaining pilot monitoring, calling out aircraft height. The landing gear was retracted at 177 KIAS and the leading edge flaps immediately deployed again reaching their normal position at a height of 56 feet AGL, the stick shaker ceased at 186 KIAS. The leading edge flaps reached their deployed position again 23 seconds after retracting, the airplane performance returned to normal thereafter and the airplane climbed out. Whilst climbing through 7000 feet the crew declared PAN reporting problems with the #2 and #3 engine and decided to return to Johannesburg. The airplane continued to climb to FL150, dumped fuel and landed safely 92 minutes after liftoff.
The leading edge Group A flaps (all leading edge flaps inboard of the outboard engines) are designed to automatically retract if the airplane is in ground mode and either reversers #1 and #4 or reversers #2 and #3 are unlocked. This design is meant to reduce wear on the flap panels, that the airflow from the thrust reversers would produce on the extended panels.
The thrust reversers did not unlock and remained in their stowed position all time, however were at the rear end of their permitted travel in high power engine operation. The stow sensors for thrust reversers #1, #2 and #3 were rigged outside the requirements with the target set too far forward thus causing the unlocked indication with the thrust reverser cowls in their permitted yet rear position.
The crew were and remained unaware of the Group A leading edges having retracted due to this automatic retraction only visible on a separate indication. Only the extended flap EICAS display would have provided them with the according information, however the display was not brought up. The only available indication was a color change of the flap display in the regular EICAS display which however is hardly visible.
The SACAA noted in their findings: "During this time the flight deck crew had no indication or understanding of what had caused the lack in performance of the aircraft."
Several safety actions are underway as result of the occurrence. Boeing plans to change the system logic withdrawing the reverser unlock signal from the autoretract logic, which would continue to function based on the reverser handles and air/ground logic. This was put into an Airworthiness Directive by the FAA.
The SACAA released a number of safety recommendations concerning the man/machine interface, spurious alerts and robustness of software and hardware control logic.
