The action that may have caused the crash of an Air India Boeing 787 Dreamliner at Ahmedabad Airport was probably not, as is widely speculated, failure to extend the aircraft’s wing flaps.
Instead, it was most likely a pilot’s decision to raise the nose of the troubled low-flying aircraft. This action was presumably taken to force it into a climb.
Otherwise, in ideal conditions – and assuming the aircraft was flying across a flat landscape with no hills or tall buildings in the way – the pilots had a slim chance of keeping it in the air and saving it. This is also based on non-deployment of flaps being a factor in the aircraft’s dire predicament.
Tragically, as amateur footage from the scene in western India suggests, the plane “pancaked” and dropped almost vertically to the ground after the nose was elevated.
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This would have had the effect of breaking up the laminar airflow over the wings, causing it to lose all remaining lift. This is similar to a manoeuvre called a flare, which pilots perform when landing. When the aircraft is almost on the runway, they raise the nose slightly to eradicate lift and make it drop the remaining short distance on to the tarmac.
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An aircraft wing is primarily designed for the high-speed flight cruise, not for taking off or landing. The area of the wings is extended to increase aerodynamic lift at relatively slow speeds while taking off and to enable an aircraft to safely make low-speed landings.
These wing extensions are known as flaps and they slide out from underneath the rear of the wing before take-off.
They are retracted back into the wing when the aircraft has reached sufficient altitude and speed before entering the phase of flight known as “the cruise”.
Without sufficient extension of the flaps, an aircraft that is fully loaded with passengers, luggage and fuel will struggle to reach altitude.
That is what happened to a Spanair jet which failed to take off and ran off the runway at Madrid Airport in 2008, killing 154 people. Investigators found that the pilots had failed to extend the flaps. The tragedy was compounded by the fact that a warning buzzer had failed to sound in the cockpit to alert the pilots to their mistake.
Raising the nose inappropriately was a contributing factor to the crash of an Air France A330 off the coast of Brazil in 2009. It caused the plane to enter a stall from which the pilots could not recover. All 228 on board were killed.
A second theory for the loss of the Air India Boeing 787 on Thursday is a bird strike against both engines, causing them to fail. This could explain the account of one witness who said he heard a loud bang a few seconds before the aircraft crashed.
However, as professional air-crash investigators will attest, eyewitness accounts are notoriously unreliable.
The replaying of the cockpit voice recorder aboard the Air India flight will reveal two important details.
First will be if the pilots correctly followed the take-off checklist, which includes procedures for deploying the flaps. One of the pilots will read out the items on the checklist, while the other one confirms that they have been carried out.
The second thing investigators will listen for is whether or not a cockpit warning was sounded to alert the pilots that the flaps had not been deployed.
Final confirmation of flaps deployment will come from a second black box, the flight data recorder, which records all of the pilots’ actions and the mechanical results aboard the aircraft.
– Gerry Byrne is an aviation journalist
