redpalmetto

So there I was minding my own business in 1D on BA1311 in ABZ when I noticed a small Eastern Airways propeller plane at the next gate (Possibly a Saab 340) getting ready to go.

What I had not seen before, however was the plane reversing back under its own power with no push-back truck, before heading out to the southerly runway ahead of our A320.

I did not realise planes could reverse (even propeller driven ones!).

KARFA

There is a term for it (which I have just found out!), powerbacks.

Jets usually have reverse thrust so could do it but don't - reverse thrust is only used on landing to slow the plane down.

For props it seems to be acceptable to use it for powerbacks. I think you get a reverse thrust on a prop by changing the angle/pitch of the propellers.

KARFA

Oh and here is a video on youtube of reverse thrust being deployed on a BA flight landing at LBA.

http://youtu.be/_6z2wQRohYg?t=1m37s

On touchdown at 1.52 you can see the door opening towards the back of the engine, and the engine noise increasing as the thrust is diverted forwards rather than backwards. The pilot releases the reverse thrust once the ground speed reaches 60 kts - the pilot monitoring usually calls out the speed I believe.

EDIT: also when the video pans over the engine at 1.58 you can see the speedbrakes are up to reduced lift and transfer teh weight to the undercarriage so the wheel braking can work effectively.

redpalmetto

Thanks Karfa - learn something new every day. Mind you perhaps the like of Ryanair might start powerbacks to save some more airport fees
I had seen (and experienced) reverse thrust before, however.

Nimrod1965

The FlyBe De Havilland DHC6 Twin Otters regularly reverse off the stands at Glasgow using reverse pitch on the propellors and they don't do it slowly either! It used to be common practice in the USA for MD80 aircraft to select reverse thrust to back off parking stands. The high rear mounted engines with "clam-shell" style thrust reversers allowed this. Low mounted under wing engines employ a different style of thrust reverse mechanisms that increase the risk of ingesting "Foreign Objects" (known as FOD-Foreign Object Damage).

DYKWIA

I remember watching AA MD-80s reversing out of their stands using reverse thrust at ORD. They had to be very careful not to brake, or they'd end up on their tail.

KARFA

Sorry, yes I should have assumed you had. I got carried away with my geekiness

Nimrod1965

I would say that the devices visible on the upper surface of the wing are spoilers, they look similar to the devices on older gliders that I have flown. Spoilers have the primary effect of decreasing lift and increasing drag therefor increasing the rate of descent. Pretty sure it's the same for passenger jets but happy to be corrected. Once the aircraft has touched down, the spoilers are deployed to effectively reduce the amount of lift the wing generates ensuring that the aircraft remains on the ground, I can't imagine that they would produce enough drag to slow the aircraft much hence the reverse thrust and then the application of wheel brakes.

If you fly on the Embraer into LCY, spoilers are used to attain the 5.5 degree glide angle.

cazoz

Is it safe to google pushing back at work?

Wouldn't be the first thing is think of, was I not on this forum!

djk7

Jets can do it too. 10-15 years ago, it wasn't too uncommon, at least in the US. I don't think it's used much any more, it uses more jet fuel, and tends to kick up a lot of debris. Here are some old threads that center on AA and NW DC-9s, but other types can do the same.

http://www.flyertalk.com/forum/ameri...thrusters.html
http://www.flyertalk.com/forum/ameri...-back-dfw.html
http://www.flyertalk.com/forum/north...w-reverse.html

Use of powered pushback in improper conditions may also have contributed to the Air Florida crash in 1982.

KARFA

I did call them speedbrakes but the function you describe is the same as I noted. The handle is labeled as speedbrake in teh A320 series aircraft and the 737. In fact I believe that will all the upper surfaces deployed it is a combination of true speedbrake and spoiler system, whereas when you use them in flight you get a much reduced panel deployment and and a shallower angle.

Here is a view from behind on a BA A319 on landing - this is my own photo and is also landing at LBA.

vibrex

Yes that's correct. Normally by a hydraulic system. An angle of around -8 degrees can provide serious reverse power.

If you'll forgive the military footage then this link shows how it's done properly Good brakes too!

Starts around 30 secs in

https://www.youtube.com/watch?v=ar-poc38C84

Sigwx

Yes power backs are common currency at the likes of ABZ. Larger Props get pushed by a tug as do Jets. As previously mentioned the Air Florida crash is a prime reason that aircraft with underslung engines do not power back as there is far too great a risk of FOD ingestion. The same is applied these days to the MD series in the US.

As for the picture, we have a mix of speedbrakes and ground spoilers. On Boeing's you can differentiate the Ground spoilers as they deflect to a greater angle than their airborne used counterparts the roll spoiler/speed brake. Generally the inboard ones are for ground use only. The outer most for roll assistance and drag.
We tend to use reverse idle when we can, reducing noise and fuel burn by simply allowing the reverser doors or 'translation sleeves' to deploy. This redirects the bypass air forward through cascade vanes. We tend to remain at reverse idle until at taxi speed/vacating the runway to reduce brake temps. In conditions where snow or some such oddity that perplexes the UK appears or has been laid, we tend to stow the reverser doors/sleeves early to avoid ingesting too much.

And yes it is the pitch angle on variable pitch propellers that enables the little puddle jumper to make a racket, rattle ones fillings, and commit to motion in the reverse. Noisy blighters

alwaysquestions

Powerbacks used to be very common (and very loud) in the US back in the 70s and 80s. As previously mentioned it was usually carried out by B727s and Dc9s and later the MD80 versions as well. Only occasionally did I see B737s doing it due to the fod risk.
The reason was mainly one of economics and speed. Firstly, you didn't have to wait for a tug to push you back which could take a while. Dallas DFW was a prime example of 30-40 aircraft starting at once. Secondly, the cost of all those extra tugs and drivers was enormous. The airlines decided that although engine life was shortened by the extra reverse, the cost saving of not using the tugs far outweighed the extra engine load.
The practice has just about died out over their now mainly because most aircraft now have under wing engines but also the noise lobby called for reductions in the engine noise.
Also, out of interest, the aircraft had to roll forwards slightly in order to get the aircraft off the tyre flats, caused by sitting in the same place, before engaging the reverse thrust to go backwards. I was worried on more than one occasion that it would roll into the terminal before it could change direction!

AQ

paul4040

I believe only the MD80, and it's older sister the DC-9, were some of the only jets allowed to reverse taxi under their own power. Anyone know why?

Edit: just reread Sigwx's post which explains about the engine positioning.