TWA772LR From United States of America, joined Nov 2011, 753 posts, RR: 1 Posted (11 months 8 hours ago) and read 5928 times:
Which is better to use during push back? What are advantages and disadvantages? I know AirTran used reversers with their 717s when I was last in ATL, but that was 2003ish... Which airlines use their reversers for push back?
All replies welcome. Feel free to add and ask anything.
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TWA772LR From United States of America, joined Nov 2011, 753 posts, RR: 1 Reply 2, posted (11 months 8 hours ago) and read 5917 times:
I imagined the tug would be best. One would think that the nose gear would have something on it to keep it from turn it too much, we know it doesn't have it on A320s. Thanks for the reply!
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Starlionblue From Hong Kong, joined Feb 2004, 15867 posts, RR: 66 Reply 3, posted (11 months 7 hours ago) and read 5881 times:
Quoting TWA772LR (Reply 2): One would think that the nose gear would have something on it to keep it from turn it too much, we know it doesn't have it on A320s.
An expert would have to weigh in but I think the tug is strong enough to break any locks on the gear turning radius.
As for 320s and the nose wheels turning perpendicular to the direction of travel, that's a safety feature. In some particular failure situations, the gear will fail perpendicular, and thus be in a predictable position, rather than at an unknown angle which would make a landing really hairy.
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Darksnowynight From United States of America, joined Jan 2012, 979 posts, RR: 1 Reply 6, posted (11 months 6 hours ago) and read 5852 times:
Quoting Mir (Reply 5):
The tug/towbar combination has enough power to overcome such things.
I think purposely. If the NLG locks and trunions were string enough to resist a tug overdoing it there, there would probably significant risk of frame damage.
On topic... Most airports have officially "no-no'd" powerbacks. I got to do one once, and looking at how vorboten it is at most places, that will probably have to do for this life.
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Mir From United States of America, joined Jan 2004, 19686 posts, RR: 56 Reply 7, posted (11 months 5 hours ago) and read 5825 times:
Quoting Darksnowynight (Reply 6): I think purposely. If the NLG locks and trunions were string enough to resist a tug overdoing it there, there would probably significant risk of frame damage.
Oh definitely. They're not there so much to prevent oversteering as to alert the crew that it's happened, and that an inspection needs to be done.
-Mir
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The only advantage of power back is that you don't need a tug...by almost every other metric, it's inferior.
Quoting Starlionblue (Reply 3): I think the tug is strong enough to break any locks on the gear turning radius.
The tug is more than strong enough. However, assuming the appropriate tow bar is in use, the fuse pins in the towbar should let go before damage to the nose gear occurs.
ak907 From United States of America, joined Mar 2012, 35 posts, RR: 0 Reply 9, posted (11 months 4 hours ago) and read 5785 times:
On any towbar, the shear pins will break first. On the 747, if the shear pins do not break, the bracket where the towbar connects to the nose gear will break. If that doesn't break, the nosegear turning actuator's piston will bottom out in the cylinder and then something serious will happen.
Why wouldn't airbus just have the landing gear lock in the normal, straight-ahead (lack of a better word) setting?
If memory serves because the gear does not have a mechanical center "detent" per se. The center position is determined somewhere else in the steering logic. So if you "lose the signal" from the tillers and pedals there is no way for the gear to know where center is. On the other hand there will be mechanical stops on both sides.
But I may be remembering that wrong.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
BoeingGuy From United States of America, joined Dec 2010, 2285 posts, RR: 7 Reply 12, posted (10 months 4 weeks 1 day 15 hours ago) and read 5537 times:
To the best of my knowledge nobody regularly does Powerbacks anymore. I'm told the AA still has it as an approved procedure and may rarely do it if a tug isn't available, but it's not a regularly done procedure anymore.
NW was the last airline I know of to stop doing it - around 2006 with their DC-9s.
AA and FL both stopped it in 2005 - AA with their MD-80s, FL with their 717s.
DocLightning From United States of America, joined Nov 2005, 16802 posts, RR: 57 Reply 13, posted (10 months 4 weeks 1 day 15 hours ago) and read 5523 times:
Quoting BoeingGuy (Reply 12): To the best of my knowledge nobody regularly does Powerbacks anymore. I'm told the AA still has it as an approved procedure and may rarely do it if a tug isn't available, but it's not a regularly done procedure anymore.
Also, it can ONLY be done with high-mounted engines. It cannot be done with under-wing engines because the risk of FOD ingestion is too high. Remember, under forward thrust, FOD will tend to get blown away from the inlet by the exhaust gas. In reverse thrust, FOD will tend to get blown TOWARD the inlet. When you are at high speed on the runway, this is less important since it doesn't get blown far enough forward, but when you are at a near standstill, you are absolutely at risk of blowing something into the path of the inlet.
Other issues:
1) Wear and tear on the engine
2) The aircraft's CG is (by design) very close to the MLG. For this reason, you have to stop the backwards roll with forward thrust. If you try to stop a backwards roll with the brakes, you are likely to tip the airframe up on its butt, which involves large amounts of paperwork, not to mention that it makes you look awfully silly.
3) The pilots don't have a rearview mirror, so if they are about to back into something, one of the spotters has to tell them, and then they have to kill the reverse thrust and then use forward thrust to stop, all of which takes a few seconds, by which point they will probably have run into whatever it was.
BoeingGuy From United States of America, joined Dec 2010, 2285 posts, RR: 7 Reply 14, posted (10 months 4 weeks 1 day 14 hours ago) and read 5472 times:
Quoting DocLightning (Reply 13): Also, it can ONLY be done with high-mounted engines. It cannot be done with under-wing engines because the risk of FOD ingestion is too high.
In practice, what you say is mostly true. However, the 757 and 737 are authorized to do powerbacks. Several customers have done it with the 737 and 757 in years past. AA tried it with the 757 but then decided not to adopt it. Britannia had a supplementary procedure in their Ops Manual for powerbacking a 757.
The 747, 767, 777 and 787 have AFM (Airplane Flight Manual) Limitations stating that "backing the airplane with reverse trust is prohibited". As I said, the 737 and 757 do not have such limitations.
BoeingGuy From United States of America, joined Dec 2010, 2285 posts, RR: 7 Reply 15, posted (10 months 4 weeks 1 day 11 hours ago) and read 5408 times:
Powerbacks are an oft repeated topic on A.net, perhaps because they were cool to watch.
bohica From United States of America, joined Feb 2004, 2407 posts, RR: 0 Reply 17, posted (10 months 4 weeks 1 day 8 hours ago) and read 5338 times:
Quoting DocLightning (Reply 13): Also, it can ONLY be done with high-mounted engines. It cannot be done with under-wing engines because the risk of FOD ingestion is too high.
EA used to powerback the 757 when they first got them. I was on a couple 757 flights departing ATL that powered back.
I still miss the good ole days on Eastern 727's back in the 80's during powerbacks. Sitting in the back of one was extremely LOUD, but was fun.
DocLightning From United States of America, joined Nov 2005, 16802 posts, RR: 57 Reply 19, posted (10 months 4 weeks 15 hours ago) and read 5126 times:
Quoting BoeingGuy (Reply 14): However, the 757 and 737 are authorized to do powerbacks.
I did not know that. Is that all 737's or just the Jurassics?
Anyway, I know that Airbus is looking into adding a small electric motor to the NLG on the A320.
BoeingGuy From United States of America, joined Dec 2010, 2285 posts, RR: 7 Reply 20, posted (10 months 4 weeks 14 hours ago) and read 5079 times:
Quoting Max Q (Reply 16): My B757 manual does not approve powerbacks.
Quoting DocLightning (Reply 19): I did not know that. Is that all 737's or just the Jurassics?
Anyway, I know that Airbus is looking into adding a small electric motor to the NLG on the A320.
So let me state this differently. There is no AFM limitation in the Boeing 737 (any minor model) or 757 AFMs that prohibit powerbacking those models. I mentioned it is prohibited by AFM limitation on the 747, 767, 777 and 787.
I can't speak for individual operator policies or other regulatory requirements. As I and others have noted, some operators have tried powerbacks with 757s and 737s. Not sure if anyone has done it with the 737NG, but it's not prohibited.
I miss watching (and riding) all the AA MD-80 powerbacks at DFW. It's kind of like the old aggressive noise abatement procedure at SNA in older model airplanes (e.g. not as quiet as the 738 which does a normal takeoff profile there). Pilots and airlines may be happy they things aren't done much anymore, but from a aviation fan point of view some of these past things are missed.
BAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 21, posted (10 months 3 weeks 6 days 17 hours ago) and read 4829 times:
Since no-one has mentioned it (in this thread at least), attempting to power back in icing/snow conditions was a major contributory factor in the loss of Air Florida flight Palm 90.
For those that don't know, the tug wasn't able to push the 737 back, so the crew attempted to power back to break the snow's lock on the gear. The engines and nacelles took on a huge amount of ice and although it certainly wasn't the only reason the plane went down, it was a large part of it.
If you get a chance, read the NTSB report, or at the very least, the Wiki entry on this crash. It's an eye-opening look into human factors and how something that might look sensible totally isn't, (snuggling up behind the aircraft in front in order to warm your plane up with his jetwash, for example).
BoeingGuy From United States of America, joined Dec 2010, 2285 posts, RR: 7 Reply 22, posted (10 months 3 weeks 6 days 16 hours ago) and read 4785 times:
Quoting BAe146QT (Reply 21): Since no-one has mentioned it (in this thread at least), attempting to power back in icing/snow conditions was a major contributory factor in the loss of Air Florida flight Palm 90.
Yes, and the other factor was being afraid to push the throttles above the target thrust even when ground contact was imminent. We talk about that in our new Ice Crystal Icing procedure. The limits may be erroneous; manually set thrust to keep the airplane doing what you want it to do.
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 23, posted (10 months 3 weeks 6 days ago) and read 4646 times:
Quoting BoeingGuy (Reply 14): the 757 and 737 are authorized to do powerbacks
In the early years....but thereafter restricted as tipping over chances existed if stopped by brakes instead of fwd thrust,hence discontinued......Our Company SOP clearly forbids powerback.
BAE146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0 Reply 24, posted (10 months 1 week 2 days 16 hours ago) and read 3593 times:
Quoting BoeingGuy (Reply 22): Yes, and the other factor was being afraid to push the throttles above the target thrust even when ground contact was imminent
According to David Beaty's book "The Naked Pilot", there was a suggestion that they were afraid of exceeding the airline's EPR limits, even though the probes and guages were essentially lying to them. The flew a perfectly servicable aircraft into a river because they were chasing numbers and ignoring the facts of their situation.
I won't criticize them for that because I'm not a commercial pilot and I'm not subject to the pressures that they were. But that was clearly a cultural problem that was just asking for an accident.
Appologies for the slight thread derailing there, but TR pushback was definitely a major factor there.
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25 BoeingGuy: When ground or water contact is imminent you firewall the engines. Exceeding thrust perimeters or sustaining economic damage to the engines is not a
26 tdscanuck: The Swissair 111 crew didn't know they had a catastrophic fire until it was far too late. Even if they'd turned around at the first indication of any
27 BoeingGuy: I sort of disagree. I helped write Boeing's Smoke/Fire/Fumes checklists and thus have studied SW111 and AC797 very extensively. Bottom line is that y
28 Starlionblue: I think the point is that they should have landed immediately. The fact they wouldn't have made it should not have influenced the decision.
29 n92r03: Classic! Plus it was just cool to watch/hear.
30 HAWK21M: Unless a tug is not available....The options of using Powerback will always be uneconomical.
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