I just heard about this 4 month old incident, where a United Airlines B777 made a U-turn, while it was on way to runway. What is the turning radius required to make such a U-Turn? Also, is so much space available near the taxi area at the IGI Airport? At last, is this a common practice for airliners to do?
Turning Radius, as found in a planning document:
- 28.7m for a Boeing 777-200
- 34.7m for a Boeing 777-300
Rotating around one a point a bit off the wing to allow both wheels to roll throughout.
Minimum Pavement Width
- 47.5m for a Boeing 777-200
- 56.0m for a Boeing 777-300
Be aware that this is not exactly ideal- visibility from the flightdeck is not great and you do not want the gear running into the grass or edge lights. An Emirates A380 screwed up in Warsaw not too long ago when trying to pull this stunt.
Since this width is not normally provided by the runway (even Heathrow only has 45m and 50m runway width), you will add turning pads at the end unless there are taxiways you can use instead.
The longest 777 s have steerable wheels on the mains and also a GMCS (ground cam showing the wheels) to assist pilot. If you want to make the smallest turn with an aircraft you have to use differential braking and asymmetrical thrust: Press hard on the toe brake on the side you want to turn, tiller full deflection and increase thrust on the opposite side. However this is some stress on the tyres and landing gear.
Data are available on that link, section 4.2 http://www.boeing.com/assets/pdf/commercial/airports/acaps/777_2lr3er.pdf
Theoretically it is possible to make a pivot turn on a B777, according to the Flight Crew Training Manual (FCTM) from Boeing.
Such a turn is started after lining up with the edge of the runway, stopping the aircraft completely,locking the brakes on the inner side of the turn and applying thrust to the outer engine on the turn. The wheels on the inner side of the turn will be really locked and subject to a high stress, and there is potential for tyre and runway surface damage. Such a turn on a B777-300 would require a minimum runway width of 43.6 meters.
It is a procedure that involves ground crew coordination and supervision and quite a risk both for the personnel involved, the landing gear and tyres and the runway surface, so it is not a normal manoeuvre, probably used only in an emergency situation where no other option is available. Having a tug to manoeuvre the aircraft around could be a much better option.