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Thrust imbalance preceded Jet 737's excursion at Goa

Indian investigators have determined that a Boeing 737-800 crew did not allow the aircraft’s engines to stabilise their thrust before the twinjet suffered a runway excursion during take-off from Goa.

The aircraft, operated by Jet Airways and bound for Mumbai, had lined up on runway 26 after backtracking and performing a 180° turn.

India’s accident inquiry committee states that the crew advanced the thrust levers to the 40% setting.

But while the left-hand engine was running at 40% of N1, the right-hand one had only reached 28% when the captain commanded full take-off thrust.

This failure to allow the CFM International CFM56 engines to stabilise led to a thrust imbalance as the aircraft accelerated.

“As soon as [full thrust was commanded] the aircraft started drifting towards [the] right,” says the inquiry into the 27 December 2016 event.

Within 10-12s the aircraft departed the paved surface and the crew attempted to brake and use rudder and nose-wheel steering to correct its course.

The jet left the runway and turned in a wide right-hand arc, eventually coming to rest facing the opposite direction and 219m from the edge of the runway.

It collided with a path-indicator lamp as well as a 2.3m pillar during the excursion, and the aircraft suffered substantial engine, undercarriage and fuselage damage.

Sixteen of the 145 occupants, all passengers, suffered minor injuries, notably during the evacuation.

Investigators state that the rejected take-off manoeuvre was conducted “incorrectly”, pointing out that only the right-hand thrust lever was retarded to idle thrust.

The left-hand thrust lever, it adds, might have been moved forward “inadvertently” as a result of the jet’s travelling over rough ground.

While the pilots had only a three-year difference in age, the captain had logged over 5,700h against the first officer’s 723h.

Investigators state that first officers should be “more assertive” with regard to adherence to standard operating procedures. The inquiry also says a call-out, confirming stabilisation of engine power, should be introduced after initial thrust application.

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