First, its pilot did not wait for the vital take-off clearance from the air traffic controller concerned. As the Boeing 737-800 aircraft sped along the runway for a take-off, the alarmed air traffic control officials hauled up the pilots and ordered them to stop. The jet had reached the critical speed of 260 kmph and was seconds away from lifting off the runway when the pilot pulled the throttle back to abort the take-off.
It was a highly controversial move, fraught with risk, as take-offs cannot be aborted at such high speeds without putting the aircraft and its occupants at risk. It did not end badly though, as the pilots could bring the aircraft to a halt before it reached the runway end. Had it been a short runway or a wet one, the aircraft could have gone off the runway. The airline has grounded both the pilots and an investigation is on. An Air India Express spokesperson confirmed the incident. The matter has once again raised questions about the training standards in Air India Express. The airline was lambasted by the Directorate General of Civil Aviation in a recent audit for its poor training practices.
"A Boeing 777 aircraft had just departed from runway 02 C and so take-off clearance to the next aircraft would have been given only after a span of two minutes," said a source. But the Air India Express pilots, operating the Singapore-Trichy flight IX-681, for reasons not yet known, decided to take off from the said runway before obtaining the mandatory go-ahead from the air traffic controller. "A Boeing 737 aircraft takes about 30 seconds to go from zero to lift-off speed, which would have been about 276 kmph, in this case," said a source. The take-off roll, though only 25-30 seconds long, is a critical stage of flight and so the flight crew operation manual-one of the books carried by pilots on board, which lists the dos and don'ts for safe flying-- lays down clear and strict guidelines for the actions that can or cannot be taken at different stages of take-off.
The rules for "Rejected Take-off" in the Boeing 737 manual say that a take-off can be rejected after the aircraft has crossed 80 knots (148 kmph) but before reaching what's called a "V1 speed" in aviation parlance, only in case of a fire, an engine failure, weather warning or if the aircraft is unsafe or unable to fly. V1 or "take-off decision speed" is the speed at or before which the pilot should decided whether to continue with the take-off or not. Once the aircraft has crossed V1, the pilot should continue with the take-off, no matter how serious the emergency, as an attempt to stop the aircraft would result in the aircraft going off the runway.
"The Air India Express Boeing 737 aircraft was critically close, about a second away from reaching V1 speed when the pilot decided to reject the take-off. It crossed the V1 speed even as the pilot pulled back the throttle," said the source.
Then the speed went down as the automatic speed brakes were deployed and the aircraft came to a halt. V1 speed is sacrosanct in flying. It is calculated using inputs like weight of the aircraft, condition of the runway, elevation of airport, temperature etc. When a pilot begins a take-off, he/she has one hand on the flying control and the other on the throttle. This is done so that the throttle can be pulled back and the take-off rejected, if say, there is an engine failure or fire warning etc.
"About 5-6 knots before the aircraft reaches V1 speed, the other pilot in the cockpit calls out V1. At this point, the pilot flying the aircraft is supposed to take his hand off the throttle," said a source. This is done to ensure that the throttle is not pulled back and take-off is not rejected once the aircraft crosses V1 speed.The Boeing 737 NG Flight Crew Training Manual says that rejecting a takeoff near "V1 has often resulted in the airplane stopping beyond the end of the runway". The finer details will be known only after information from the Digital Flight Data Recorder and Cockpit Voice Recorded is studied. Among critical questions are when did the ATC ask the pilots to reject the take-off and how many seconds elapsed before they decided to do so? Why did the pilots decided to do the high-speed reject when they knew the aircraft was very close or almost at V1 speed? Both pilots were from Air India, deputed on Air India Express.
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