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Can commercial airliners theoretically taxi backwards using reverse thrust?

If this is possible, why isn't it common? I can already imagine some safety reasons but it would be nice to hear it from someone who knows :-)

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Very common on turboprops as the prop angle can be changed to produce reverse thrust a lot more efficiently than a jet thrust reverser! –  Brian Knoblauch Aug 11 at 19:14
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I have seen it done with DC-9s many years ago. –  Cimbian Aug 12 at 18:04
    
@Cimbian Yes, this used to actually be very common with DC-9 class aircraft. I saw DC-9s to powerbacks all the time in the 90s. With fuel prices nowadays, though, it's no surprise that they almost universally opt for tugs instead now. –  reirab Dec 9 at 15:14

2 Answers 2

up vote 33 down vote accepted

This is called Powerback, most aircraft can do it, but it is not done very often.

In a jet aircraft, the three main problems are:

  • Reverse thrust tends to throw a lot of debris into the air because the exhaust is deflected to the sides and up and down too. This debris can damage both the engine itself and other things around the aircraft. It is less of a problem for aircraft with tail-mounted engines (so DC-9s often used powerback), but that engine configuration is not used as much any more in transport aircraft, as it is less aerodynamically efficient.
  • Reverse thrust is rather inefficient on jet engines, so it uses a lot of fuel.
  • As Casey mentioned in the comment below, the pilot has to be careful using the brakes during powerback: the main wheels are behind the centre of gravity, so harder braking can lift the nose wheel, causing the pilot to lose control and even causing damage to the tail if it hits the ground.

So a tug is both cheaper and safer.

In propeller aircraft, reverse is more efficient and does not throw up as much debris, so it is sometimes used. But a tug is still preferred because transport aircraft don't have any rear visibility, so the pilots can't see where they are taxiing. With tug the driver can see behind the aircraft, and a ground marshaller walks along side each wingtip with an intercom connected to the plane.

Lastly, since aircraft are able to turn almost on the spot using differential braking and thrust and 180-degree nosewheel steering, at airports with few facilities there is generally enough space around the aircraft to permit the pilot to reverse out easily.

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I didn't think about the fuel consumption. Nice answer, thanks! –  André Stannek Aug 11 at 11:21
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@AndréStannek wheels are aft of CG, so braking will create a nose-up torque and sit the airplane on its tail. Standard procedure during powerbacks is "feet on the floor" to avoid inadvertent brake application. –  casey Aug 12 at 12:00
    
Isn't the prevention of compressor stall also another reason that powerbacks aren't used in most aircraft? This is also one of the reasons that reverse thrust has to be cancelled relatively early in the landing rollout, too, right (along with FOD prevention?) –  reirab Dec 9 at 15:24
    
@reirab: I don't know. I always only heard the FOD argument, but I don't know enough to claim it is not true. –  Jan Hudec Dec 9 at 20:40

It can be done, in fact the DC-9 and MD-80 aircraft are approved for backing up using reverse thrust. It is called "powerback".

It is rarely used since it is quite fuel consuming, noisy and increases the risk of sucking up debris near the gate area causing damage to the engines.

Here's a video of an MD-80 backing up.

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Those reversers deploying look like something out of Transformers! –  David Richerby Aug 11 at 10:35
    
@DavidRicherby would you believe that it's only 2 links and an actuator to get that movement? –  ratchet freak Aug 11 at 10:42
    
Wow, seeing a plane back up be itself just seems wrong :-D Thanks! –  André Stannek Aug 11 at 11:18
    
Wow that powerback is NOISY! –  shortstheory Aug 12 at 10:07
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@SkipMiller It is a trade-off between fuel consumption (and perhaps maintenance costs) for powerback, or labor costs and equipment costs for pushback. The 30-40 seconds may not be much compared to the total fuel costs but it may still be more expensive than a lowly paid pushback truck driver for 5 minutes. It is a beancounters decision in the end. –  DeltaLima Aug 12 at 15:48

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