they do this everywhere. sounds like it's to make sure there's nothing left in the path of the wheels (chocks, bags, small children etc) and that the brakes are really off.

wonder if a DC-10/MD-11/TriStar could do it with the tail engine...

Nope, you need thrust reversers to power back.

The reversers are pieces of metal that are pulled from the cover of the engine and places just behind the engine causing the thrust to reverse. This is impossible on tail mounted central engines like in the DC10, MD11, L1011 and the 727(center engine). It's possible only on those engine mounted sideways like DC9, F100, MD80, 717 and the side engines of the 727.

Now THAT I'd like to see (but hopefully not at 35,000 ft).

(but I catch your drift)


[This message has been edited by AndrewC75 (edited 04-17-2002).]

Hi Y'all,

Powerbacks are very common here at DFW (and standard thru the AA system).

The rolling forward at the start is to getthe plane off the "flat spots" on the tires. Aircraft tire aren't pumped up to a high pressure (heat from braking causes the air...actually nitrogen mix...inside to heat and expand; need low pressurre to allow for expansion). Therefore, while sitting at the gate, the weight of the plane causies the tire to get "out of round". It's preferred to go forward to get off the flat spot cuz too much power in reverse is bad...it throws all the debris into the front of the engine only to get sucked up and cause possible damage.

Eastern used to powerback 757s. AA did on their 1st 757 flight (DFW to SNA..Orange County CA) but it needed so much power that they immediately suspended future 757 powerbacks.

Tail mounted engines on 727, DC-10s etc do have thrust reversers.

Steve

er, DC-10 et al have thrust reversers on the tail engines, although these aren't the clamshell type used on DC-9 etc. they're more of a sliding shroud.

and I've seen the center engine of a 727 reverse when it powered back next to the DC-9 I was on at MSP. it's hard to see, as there's no clamshell on NW 727 engines, but you can see it happen if you're at the right angle. there's an internal pivoting bowl-shaped thingie that reverses thrust on those 727s.

"It's very common, but seems to be even more common at the new terminal."

The reason they didn't do it at the old terminal is because at this "logistically challenged terminal" (understatement of the century) it was impossible to do powerbacks because there simply was not enough room.
Furthermore, powerbacks have to be FAA approved before an airline is allowed to perform them at any one particular airport.
Also, you won't see any powerbacks during heavy rain or snow in order to prevent injury and/or damage.


"Less ground people working = less tugs in use, and less groundpeople to signal the plane into "brakes up" at the gate."

Less tugs yes, less groundpeople no.
It takes the same amount of people. In an ordinary pushback you need one person in the pushback tug and two wingwalkers. In a powerback you need one marshaller directing the pilot and two wingwalkers.

This clamshell design tends not to be used on new engines. While it is very efficient, it is more prone to mechanical problems. Newer engines have sliding panels that open exposing the reversing vanes.

Turnouts (when the jetway or boarding bridge goes as far back as possible) are common in many cities, especially at smaller airports. A turnout's only issue is that it tends to blow FOD (foriegn object debris) out of their crannies and onto the ramp, so while it may be faster, the rampers and marshaller have to do a visual inspection of the ramp after the aircraft departs. the aircraft also needs to be pointed at at least a 20 degree angle to the terminal inorder to do it successfully.

For a powerback, almost *AnY* plane can do it, including turboprops. They are faster than using a tug, but the only issue with powerback is 1. do you want to burn up that much fuel 2. is the ramp dry enough to allow it 3. braking action. Powerbacks are common with tail mounted jets (DC9s, 727s) but they can be done by 747s, MD 11s, DC10s, L1011s, but it just burns up so much fuel doing it, that it isn't done. (FYI, all engines have thrust reverse).

-nate

Enough has been said above about this common practice with AA at DFW. You can be sure that the engine folks at P&W have signed off on the practice as well, so I feel that any suggestion that there is additional wear and tear on the engine is unfounded. However, I would agree that the tarmac must be free of loose debris to avoid F.O.D. to the engine(s).

We call it a "power back." Besides the 9, the only other aircraft that can power back is a 727. Sometimes it is quicker to powerback rather than wait for a tug to push back. A note of interest - the old Metro Wayne County Airport in DTW (may it burn to the ground!) did not allow for power backs. Too congested.

From what I can recall, it seems like many flights on the green concourse at MSP have used powerbacks for at least 10 years. The gates on most of the other concourses at MSP are too close together to have enough room for powerbacks.

The majority of the time that we were departing from the gold concourse, we did a powerback. And the pilots really zoom it back. It's better than waiting on a tug but hard for us who are performing the safety demonstration while powering back.I have wound up in someone's lap before.

My understanding is that Eastern was the first airline to conduct powerbacks, and that it was a source of some labor controversy when it was first done (not sure why, as people have already indicated that it doesn't lessen the number of ramp employees required for the jet to push back).

As for breaking the flat spot on the tires, I think this is done going forward because the engines are more efficient in "normal flight" mode and thus better able to break the flat spots rolling forward rather than rolling back.

9 year old thread brought back to life...