Does an aircraft use its engines to taxi or is it always pulled by some other vehicle?
I have seen a small lorry pulling it sometimes; is it really pulling the huge thing, or does the aircraft use its own power somehow?
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4$\begingroup$ For the single engine airplanes that most of us probably fly, it's quite normal for a single person to push/pull them around by hand. Often the plane comes with a tow bar that has a handle and hooks on the nose gear. $\endgroup$– jamesqfCommented Dec 2, 2016 at 19:17
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3 Answers
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Aircraft are not always moved with tugs (the small vehicle you refer to). Much of the time, they operate under their own power.
Airliners are generally pushed back from the gate using a tug, as that's the simplest and most efficient method. They then taxi to the runway (and all the way up to the gate, after landing) using their own engines to provide thrust. This is true of both jets and propeller aircraft.
Some work is being done on self-contained electric-powered ground propulsion; one major player in this area is a company called WheelTug. They use high-torque motors and the aircraft APU to allow the aircraft to move itself without starting its engines or requiring a tug to be connected and disconnected.
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$\begingroup$ There was at least one airline back in the 60s or 70s that was powering-back 727s for awhile at some stations. $\endgroup$– TerryCommented Jan 12, 2014 at 22:09
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$\begingroup$ @Terry yeah, that's true. DC-9s occasionally did this as well (Northwest, maybe?) but it's not very common. But yeah, that's why I didn't say that airliners always get push backs! $\endgroup$– egidCommented Jan 12, 2014 at 22:36
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$\begingroup$ AA was doing it into the 90s if memory serves correctly. You have to have an Opspec to do it though. OPSPEC C065, POWERBACK OPERATIONS WITH AIRPLANES. A. C065 authorizes the use of powerplant reversing systems for rearward taxi operations... $\endgroup$ Commented Aug 12, 2014 at 23:57
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1$\begingroup$ Yeah, I remember both AA and Northwest doing powerbacks commonly back in the 90s. I guess with the price of fuel, it wasn't as expensive back then as it is now. $\endgroup$– reirabCommented Dec 23, 2014 at 7:17
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1$\begingroup$ @reirab Well, and then there are drive-in jet bridge stands such as some on CDG T1 :) goo.gl/maps/jRMB3BXrRt92 $\endgroup$– yo'Commented Sep 16, 2017 at 12:52
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Usually an aircraft taxies under its own power. Aircraft have no powered wheels, so the forward thrust comes from the engines. Only pushback from the gate is mostly done by a tractor, although some aircraft can use reverse thrust for that.
When the aircraft is being moved for maintenance purposes or simply relocation at the airfield, the aircraft is usually pulled.
Research is going on into fitting electro motors into aircraft wheels so that they can taxi without having to start the engines. Lufthansa has done some experiments. The concept would save taxi fuel and is more friendly to the airport environment (noise, polution), however the additional weight of the motor drive system would offset these benefits because it causes additional fuel burn during flight.
answered Jan 12, 2014 at 21:04
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$\begingroup$ taxies under its own power? do you mean its engines or its wheels have some sort of power? $\endgroup$– shabbyCommented Jan 12, 2014 at 21:07
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1$\begingroup$ @shabby, "under its own power" means thrust produced either by turbine or propeller, depending on powerplant. $\endgroup$– caseyCommented Jan 12, 2014 at 21:28
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Most aircraft taxi using their own engine power. Tugs are usually only used to get an aircraft to a safe distance away from all structures, people, and other aircraft before engine start, or if the engine(s) are inoperable (maintenance, mothballing, etc.). However, there is a system (called the ElectricGreen Taxiing System, introduced at the 2013 Paris Air Show) that attaches to the wheel and uses an electric motor to move instead of the main engine(s). It is currently only available on the Airbus A320 family and the Boeing 737 family.
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1$\begingroup$ I would say more than just "a safe distance away". The idea would be to get the aircraft pointed outward so that it can thenceforth move forward under its own engine power. And aren't engines usually started at the gate anyway? It's just that it's usually not desirable to try to back up under engine power (discussed many times in this site). $\endgroup$ Commented Jun 30, 2014 at 14:30
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$\begingroup$ Using electric or hydraulic drive on wheels to permit self-powered pushback and taxiing is an interesting idea, but adds weight that has to be justified for other purposes (such as braking during landing?). Unlike a hybrid car, there's not much you can do with energy generated from the wheels. Also, using a tug, visibility to the rear from a tug and ground crew is usually going to be better than from the cockpit, reducing the chances of bumping into another aircraft on the ground during pushback. Maybe rear-view cameras would be installed? $\endgroup$ Commented Jun 30, 2014 at 14:35
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$\begingroup$ @PhilPerry I think the systems he's referring to here is actually a separate vehicle, not an electric motor that is actually carried on board during flight. Those have been proposed, too, but they suffer from the weight problem that you mention, which is especially problematic on aircraft that spend much more time flying than taxing (such as long-haul aircraft.) $\endgroup$– reirabCommented Dec 23, 2014 at 7:20
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$\begingroup$ It's not for pushback (well maybe it is but that's not the purpose). It's for taxiing on the taxiways, saving a lot of fuel from not taxiing under engine power. $\endgroup$– ptgflyerCommented Dec 25, 2014 at 16:33