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?
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14$\begingroup$ The Daily Mail is a notoriously sensational, inaccurate newspaper and in this case I think the term "U-turn" is used figuratively, not literally: the aircraft simply returned to the gate and the artwork even shows it following a semi-circular taxiway. On the other hand, your question about the turning radius is a good one. $\endgroup$– PondlifeCommented Jul 24, 2015 at 14:35
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1$\begingroup$ As can be seen on the IGI airport diagram, there is plenty of space where an airliner could "turn around" and head back to the gate. Worst case, they would roll to the runway, and instead of starting, just roll down the runway to the next "exit". $\endgroup$– AlexanderCommented Jul 24, 2015 at 14:41
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$\begingroup$ From looking at aerial photos of Kjevik airport, Kristiansand, Norway, I can confirm that a 737-class airliner needs no more than a 60m circle of tarmac for a U-turn. $\endgroup$– AlexanderCommented Jul 24, 2015 at 14:45
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1$\begingroup$ The picture in the article is an illustration, it isn't reality. My point is simply that "U-turn" only means that the aircraft returned to the gate. It doesn't mean that it literally turned around in the taxiway. The article is taking an unusual but not inexplicable event and turning it into a 'drama' with hints of conspiracy theory. This is entertainment, not a factual, accurate news report. $\endgroup$– PondlifeCommented Jul 24, 2015 at 15:36
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1$\begingroup$ @Pondlife as you already pointed out, U-turn is not return to gate. U-Turn is U-turn and return to gate is return to gate. It's just that Daily Mail is inaccurate, to the point that one may call its articles misleading. $\endgroup$– AlexanderCommented Jul 24, 2015 at 15:48
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3 Answers
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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.
answered Jul 24, 2015 at 14:46
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2$\begingroup$ Or to explain they pivot around one of the main gear. $\endgroup$ Commented Jul 24, 2015 at 14:49
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2$\begingroup$ @ratchetfreak it doesn't quite pivot around the main gear, but it's close. $\endgroup$– foootCommented Jul 24, 2015 at 14:54
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1$\begingroup$ I would imagine pivoting on a single wheel would mar the pivoting tire, so it must roll at least a little. $\endgroup$– corsiKaCommented Jul 24, 2015 at 21:46
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$\begingroup$ @corsiKa: Right, and the 777 has a 6-wheel dolly. Pivoting around one tire would not be possible - the forward and rear ones would need to move sideways at full load. $\endgroup$ Commented Jul 24, 2015 at 22:22
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2$\begingroup$ @anshabhi Doing a 180 degree turn on a runway is a regular occurrence at some airports. For example, take a look at the taxi diagram on page 10-9 of uvairlines.com/admin/resources/charts/SAEZ.pdf for Ezeiza International at Buenos Aires. If you're landing on rwy 17 and roll past the intersection with rwy 11/29 you have to do a 180 on the runway as there is no parallel taxiway. There is a turnaround at the end of rwy 17, but if you're down to taxi speed just past the intersection, there's no point in wasting the time and fuel to taxi to the end. At least I never did. $\endgroup$– TerryCommented Jul 25, 2015 at 1:26
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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
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$\begingroup$ The aft two wheels on the mains are steerable on a a 777 but are limited in their turn radius and do not engage unless the commanded turn is pretty sharp, as I recall from my days at Everett. $\endgroup$ Commented Nov 13, 2016 at 16:22
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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.
