48

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...

fooot
  • 72,860
  • 23
  • 237
  • 426
André Stannek
  • 1,541
  • 2
  • 15
  • 21
  • 2
    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 '14 at 19:14
  • 1
    I have seen it done with DC-9s many years ago. – Cimbian Aug 12 '14 at 18:04
  • 1
    @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 09 '14 at 15:14
  • 5
    I've powered back King Airs, Metroliners, and 727s without difficulty when tugs were not quickly available. An acquaintance powered back a 747-200 when a tug couldn't be maneuvered into a position that it could do it. His is the only incidence of a 747 being powered back that I'm personally aware of. – Terry Feb 23 '15 at 21:10

3 Answers3

55

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 the engine itself, other things on and around the aircraft or injure someone on the ramp. 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.
  • A related problem is that the compressor might suck in its own hot exhaust gases. This might lead to temperature-induced damages in the last (high-pressure) stages of the compressor and health issues for passengers, since the air conditioning system works with bleed air from the compressor.
  • 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 very close 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 (“tail-tipping”).

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.

Community
  • 1
Jan Hudec
  • 56,247
  • 12
  • 155
  • 268
17

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.

DeltaLima
  • 83,202
  • 11
  • 272
  • 366
  • 1
    Those reversers deploying look like something out of Transformers! – David Richerby Aug 11 '14 at 10:35
  • @DavidRicherby would you believe that it's only 2 links and an actuator to get that movement? – ratchet freak Aug 11 '14 at 10:42
  • Wow, seeing a plane back up be itself just seems wrong :-D Thanks! – André Stannek Aug 11 '14 at 11:18
  • Wow that powerback is NOISY! – shortstheory Aug 12 '14 at 10:07
  • @DavidRicherby those are known as target/bucket reverse thrusters: http://en.wikipedia.org/wiki/Thrust_reversal#Target_type – shortstheory Aug 12 '14 at 10:09
  • I'd like some reference for the high fuel consumption argument. Sure the engines have to power up substantially to make sufficient reverse thrust (as the buckets that direct the exhaust are not perfect at creating reverse thrust) but in the context of fuel burned during a flight, the 30-40 seconds of reverse thrust doesn't seem like it would be a significant factor in the overall fuel planning. Correct me if I am wrong! – Skip Miller Aug 12 '14 at 13:31
  • 2
    @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 '14 at 15:48
  • 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... – Sports Racer Aug 13 '14 at 00:00
  • Dang, that MD-80 backing up was pretty neat! – CrossRoads Jul 13 '18 at 15:49
  • AAL, which has a large MD80 fleet, used to powerback from gates. They switched to tugs at their hubs rather quickly when oil prices doubled almost overnight, but they sometimes still do it at non-hub airports, when not needing to wait on a tug would likely save enough time/money to justify the wasted fuel. – StephenS Nov 27 '18 at 22:21
6

Can commercial airliners theoretically taxi backwards using reverse thrust? - After an airshow at RNAS Yeovilton, Somerset in the 1980s a British Airways Concorde found it could not taxi out for departure as it had been parked too close to an adjacent hangar (and didn't have the required turning circle)... there was no suitable towing gear on site, or within easy reach... so after a discussion with his engineers the pilot decided to reverse taxi a short distance using reverse thrust.... the centre of gravity was adjusted by transfering fuel to the forward fuel tanks, fingers were crossed, and... it worked! (I was there to see it, working in the control tower)

Tim Brown
  • 61
  • 1
  • 1