2 days ago
Air India plane crash: Were Boeing 787's flaps retracted?
Several aviation enthusiasts and experts have speculated whether the flaps of the Air India 171 (Boeing 787 Dreamliner), which crashed on Thursday in Ahmedabad, were retracted while analysing the video of the crash.
Flaps are retractable surfaces on the trailing edge of wings. An aircraft, during the take-off and landing phases when its speed is slow, requires extra 'lift' — the upward, aerodynamic force generated by the wings that keeps a plane aloft.
This extra lift is provided by the flaps, which increase the wing surface area. Flaps are extended by either of the pilots manually before take-off and landing. Extended flaps are set at different degrees depending on requirement. In all other phases of flight, the flaps remain retracted.
Crashed Dreamliner's flaps
It appears from the pictures of the wreckage that the flaps were in an extended position, and not retracted, as speculated.
Extending the flaps for take-off is part of the 'before take-off' checklist and is done on the ground when the aircraft is on the apron or taxiway. This takes place much before an aircraft enters the runway, and begins its take-off roll and gets airborne.
If the crew misses this vital checklist item, the 787's warning system will warn the pilots about the incorrect flap settings.
Speaking to The Indian Express, Greg Feith (67), former senior air safety investigator with the US National Transportation Safety Board (NTSB), said: 'The thing that's curious about the video is that the flaps appear to be up or at a minimal setting that wouldn't be typical of a normal takeoff.'
David Learmount, Consulting Editor, FlightGlobal, on his blog wrote, 'Looking at a video of the last few seconds of the flight, the landing gear still remains down, the flaps look as if they are still at a take-off setting, and the aircraft is in a steady descent which only ended in impact with buildings and the ground'.
As for why the landing gear was still down, it is likely that the pilots, dealing with the emergency, had no time to retract the gear.
V1, Vr, V2 speeds
These are three critical speeds during the take-off phase.
Rolling down the runway for take-off but not airborne yet, as an aircraft attains V1 speed, the plane's Captain has to decide whether to continue or reject the take-off. If the Captain feels something is not alright, it is her last chance to stop the take-off. V1 is also called the take-off decision speed.
Once an aircraft has crossed the V1 point, it is unsafe to reject the take-off as the available runway length may be insufficient to stop the aircraft.
Vr is the rotation speed or lift-off speed. At this point, the monitoring pilot calls 'rotate' and the pilot flying gently raises the nose. The wings are producing sufficient lift and the aircraft becomes airborne.
V2 or the take-off safety speed is the minimum speed at which an aircraft can climb safely with one engine.
V1, Vr and V2 speeds vary for every flight, calculated on the basis of aircraft weight, runway length, weather etc.
From the videos, it is evident the Air India 171 did not encounter any problems during the V1 and Vr phases, but experienced problems during the climb phase.
