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When pushback is connected to the nose gear, can the pilot release the aircraft's parking brakes while the pushback vehicle's "hand-brake" is set? Can it hold the weight of the aircraft?

Any regulations or SOPs that are covering this question?

Pondlife
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m sayed
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  • On flat ground? On a hill? Sitting on ice? Engines idling? Engine run up? – Ron Beyer Jul 07 '21 at 00:09
  • @Ron Beyer, At gate while engines are off (flat ground). – m sayed Jul 07 '21 at 00:15
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    Then yeah, gravity and static friction will do most of the work there... If you put your car in neutral on a flat driveway, does it roll away? Even small chocks will stop any movement. – Ron Beyer Jul 07 '21 at 00:18
  • On flat ground, you can release the brake & the aircraft won't roll anyway. With enough slope, it could roll. (But the tug, brakes set, would prevent that.) – Ralph J Jul 07 '21 at 00:18
  • Thanks for your replies.. The last question please; Do pilots & ground staff do it, say if there's a delay or traffic behind and the pilot has been asked to release the parking brake, the tug set its own brake or they ask the pilot again to set the parking brakes? Is there any SOPs or regulation to prevent doing that? – m sayed Jul 07 '21 at 00:25
  • Your 2nd question in the comments deserves to be its own question. That's how the system here works - one question per "question" box. Questions/answers in the comments can get lost in the shuffle or even deleted. You'll learn all this and more if you'll spend a minute or two taking the [tour]. – FreeMan Jul 07 '21 at 15:21
  • What particular aircraft and vehicle? Not really answerable because it depends on many factors. – jamesqf Jul 07 '21 at 16:51

2 Answers2

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The tug operator talks to the pilot through an intercom connected directly into the airplane's audio system, and when the pushback is ready to start, the tug will confirm PB release with the pilot before the movement starts.

If the tug operator doesn't have voice communication with the crew, hand signals are used, parking brakes off being two closed fists held up, then hands opened with palms toward the pilot (brakes on is the opposite).

The tug is quite heavy, with powerful brakes, and has no problem slowing down or holding the mass of the aircraft at the walking speeds being used.

If the tug driver has to stop during the pushback, the driver will carefully slow and stop the tug, and depending on how long they expect to wait, or if some other conditions exist like a slope or a strong wind that wants to push the plane along, may tell the pilot to reset the parking brake as well. Or they may just sit there relying on the tug's brakes, especially if it's expected to be a short 10 or 15 second wait. Depends on the situation and the operator's judgement, and airline SOPs that dictate minimum actions.

SOPs for that will depend on the airline. You also have manufacturer's towing (and taxiing) procedures, covered in Chapter 9 of the Aircraft Maintenance Manual, and airline SOPs will typically be based on that, possibly with their own custom procedures thrown in.

John K
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Yes, they can. Planes generally* don't have any kind of automated communication with the tug. The brakes, power, etc. are all coordinated by hardwired (voice-only) intercom, (voice-only) radio, hand signals, signal lights, or something similar. So there's no interlock that prevents the pilot from doing whatever they want with the brakes at any time.

Airplane tugs are big, heavy things with oversize brakes, specifically because they're designed to move bigger, heavier things. Typically, the airplane's brakes aren't used at all during the pushback, the tug does all the braking itself. So, yes, its brakes would be quite capable of keeping the plane still without any help.

As far as I'm aware, there are no specific regulations on the use of plane brakes vs. tug brakes. Rather, the airplane's manufacturer and/or the airline will have a set procedure to use, and there may be (depending on jurisdiction) a regulation that says you must follow procedure.

*I don't actually know of any exceptions to this, but I'm not exactly a guru of all things pushback-related either.

HiddenWindshield
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    You've never seen a ground person hooked up to the aircraft with a headset? It's pretty common... https://aviation.stackexchange.com/questions/13816/how-are-pushbacks-coordinated-between-the-pilot-and-the-tug – Ron Beyer Jul 07 '21 at 01:40
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    @Ron, I don't see anything in Hidden's answer saying that wasn't an option. They said that there generally isn't automated communication between the tug and the plane, e.g. an interlock, and that instead everything is coordinated by radio or hand/light signals. – randomhead Jul 07 '21 at 04:13
  • What is meant by "automated communication"? – Michael Hall Jul 07 '21 at 04:30
  • @MichaelHall Maybe I phrased that wrong. I was referring to some kind of interlock that would let the tug (or the tug driver) control the plane's brakes directly, as opposed to talking to the pilot and having them set or release the brakes. – HiddenWindshield Jul 07 '21 at 04:56
  • @RonBeyer I was including that under the "something similar". I'll add that to my answer so as to be more clear. – HiddenWindshield Jul 07 '21 at 04:58
  • Well, I don't think "automated communication" is a useful term here. It doesn't add any clarity, and the meaning is fuzzy in almost any context. Communication, (by definition and between humans...) really must be a manual process to transfer thoughts to another person. (via speech or text, aided by intercom, radio, etc.) What is there to "automate"? – Michael Hall Jul 07 '21 at 16:09
  • @MichaelHall In a big truck, when you step on the brake pedal, it applies the trailer's brakes as well as the cab's. This happens automatically, without the driver needing to select it. Yes, it's done by air pressure rather than electronically, but the principle is the same. It would be pretty simple to do something similar in aviation, with a tug automatically applying the plane's brakes via a data link when the tug's driver presses the brake pedal. The OP asked if the pilot could control the brakes independently of the tug. The answer to that is "yes", because such a link doesn't exist. – HiddenWindshield Jul 07 '21 at 17:24
  • @HiddenWindshield: OK, I get your point now. I just wouldn't call electric trailer brakes "automated communication". (I interpreted "communication" to mean human coms, like plugging in a headset...) Maybe there is a better way to state this, but it's up to you if you want to edit more. Just my two cents worth. – Michael Hall Jul 07 '21 at 19:39
  • @MichaelHall Yeah, that might not have been the best word to use, but I was trying to be inclusive of such things as a computer on the tug communicating with a computer on the plane to control the brakes. Like I said, if you've got a better way to put it, I'd be happy to edit. – HiddenWindshield Jul 07 '21 at 22:01
  • @HiddenWindshield, maybe something like: "there's no interface or controller that allows the operator to apply the aircraft brakes from the tow vehicle"? – Michael Hall Jul 08 '21 at 02:34