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Jumbo Jet Powerbacks  
User currently offline747buff From United States of America, joined Jan 2001, 744 posts, RR: 0
Posted (12 years 7 months 3 weeks 6 days 1 hour ago) and read 1454 times:

I have read about powerbacking, where a plane backs out of the gate using reverse thrust. I think it is mostly done by DC9s, MD80s, 727s, and 732s. Is it possible for big planes to do this, such as a 747 or 777?


At Eastern, we earn our wings every day!
4 replies: All unread, jump to last
 
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 1, posted (12 years 7 months 3 weeks 5 days 19 hours ago) and read 1388 times:

Powerbacks are much less suited for aircraft with underwing engine pods due to the risk of ingesting whatever the reversed airstream stirs up.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineBroke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 2, posted (12 years 7 months 3 weeks 5 days 17 hours ago) and read 1370 times:

I worked for Eastern Airlines, which I believed was the first airline to regularly use powerbacks at the ATL terminal in the early '80's. On wide body airplanes there are a couple of problems which negate the effectivenss of powerbacks. First, the thrust reversers on wide bodys only reverse the cold stream. So on a powerback, the hot stream would be providing forward thrust, while the fan air is in reverse. This is fine on the runway where the airplane is in motion and slowing, but it makes overcoming the inertia of a big airplane at rest very difficult. Second, the possibility of generating a considerable amount of debris, that could include things as large as cargo containers and vehicles by the reverse fan air, is very likely.

User currently offlineWilcharl From United States of America, joined Jun 2000, 1168 posts, RR: 3
Reply 3, posted (12 years 7 months 3 weeks 5 days 14 hours ago) and read 1347 times:

EA regularly powered back the 757s it was surpisingly quiet. AA tried it for a while on the 75 apparently and foded up one to many engines and decided to use pushbacks. I met a MX guy once that said he did it with a 747 freighter on a remote pad one night

User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 4, posted (12 years 7 months 3 weeks 5 days 4 hours ago) and read 1279 times:


Almost any jet can do a powerback.

The question is "can a jet SAFELY do a powerback"?

The answer is no for the 747.

Jets with tail mounted engines such as the 727, DC-9, MD-80 series, MD-90 series, 717's can safely do powerbacks.

To do a powerback you increase power a bit, release the breaks, and roll forward a bit, pull back to idle, put on the reverse (reversers won't activate unless you're in idle, at least on modern jets), apply a bit of power and start backing up. Once momentum is established little reverse is required after that, the rest can be done on idle, the tiller is used for steering (duh). No breaking unless you want to see the sky prematurely. Once you're done backing up, bring the engines out of reverse and back to idle.

Increasing power, increases engine RPM, which in turn results in an increase in air being sucked in. If the engines are mounted high up (such as tail mounted engines) there's a small risk of foreign object damage.

Low mounted engines however present a much greater probability of FOD. This by the way can include ramp-workers  Wow! . Very dangerous.

Many aircraft with wing-mounted engines such as the 747, use high-bypass turbofans. Turbofans reverse cold-stream only as a rule. Some do not though. (The first DC-10's and L-1011's reversed both hot and cold stream, but they were taken out because they only made up a small percentage of overall braking power). The hot-stream is still in forward thrust so when you start applying power to back up, you're also applying some forward thrust too (some is shooting out the back). An unsuspecting truck passing by and BAM! They're suddenly flying a couple of hundred feet. OUCH!  Wow!

Most tail-engined aircraft dont' even do powerbacks because of the noise produced. The only reason you would do that is if you had no ground equipment available. Airlines like Northworst for example do powerbacks frequently.

Eastern Airlines as an interesting note did powerbacks with some of their small aircraft up to the 757 in size! AA did the same thing and had FOD problems. I hope they didn't suck in anybody, but they did get their engines fodded up one time to many and they said f**k it! They now do regular pushbacks with 757's, no more. The MD-80's and up to recently their 727's  Sad performed powerbacks.

-AVK



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