The headlines never stop giving...(apparently I used this title before).

[brianw999]

To be honest I think it’s time to close this thread. We have one real life heavy driver giving the chapter and verse on how it all works versus, at best a bunch of flight sim drivers.

[BoeingBobby]

Perhaps we should.

Sorry to make such a big deal, but locking the brakes is generally not the best way to stop a broad range of things...including a 747 NOT_doing a rejected take off.

It's strange that you do not comprehend the seeming inconsistency.

(Please note carefully chosen wording)

https://www.youtube.com/watch?reload=9&v=_g6UswiRCF0

[Evan]

https://www.youtube.com/watch?reload=9&v=_g6UswiRCF0

I don't see any wheels locking there. I do see fuse plugs deflating the tires due to convective brake heat.

[BoeingBobby]

I don't see any wheels locking there. I do see fuse plugs deflating the tires due to convective brake heat.

Did I EVER say ANYTHING about wheels locking up?

[ATLcrew]

To be honest I think itÂ’s time to close this thread. We have one real life heavy driver giving the chapter and verse on how it all works versus, at best a bunch of flight sim drivers.

You'll have to close quite a few threads then...

[ATLcrew]

Why does this bug you? All 3 airlines that I flew for did Steep turns in the Sim that way. ATL?

Same here.

[Gabriel]

For what is worth, I have to side on Evan's and 3WE side here.

I have no specific information about how any specific antiskid and/or autobrake system works in any specific airplane type.

But I do have a general idea of the general concepts involved in designing and operating these systems in general, and I don;t see any reason why the antiskid would not operate in parallel with the autobrakes in any mode. In particular:

- I don't see any reason why, from an airplane operation point of view, it would be undesirable that the antiskid operates together with the antiskid in any mode including MAX and RTO. Rather the contrary. Skidding worsens (lengthens) the stopping distance, kills directional control, and at any med to high speed almost guarantees the destruction of the tires during the roll out, and possibly the damage of many other components in the landing gear assembly (it does prevent brake wear, though). On the other hand, a working antiskid guarantees the minimum stopping distance, keeps the directional control intact, and maximizes the possibility that the tires remains inflated until the plane stops (then the fuse plugs are likely to melt and deflate the tires, but the plane is already stopped).

- I don't see any technical reason that would make it difficult, economically unfeasible, unsafe or unreliable for the antiskid to work together with the autobrakes in any mode, including MAX and RTO. On the contrary, it would be simpler and cheaper to have the antiskid work in "its own world" regardless of and even ignoring whether the autobrakes are in mode MAX, RTO, 1, 2, or any, or even if it is the pilot feet or the autobrake who is actuating the brake.

BB, I cannot say for sure, but my engineering intuition (which is not infallible) tells me that this time you are wrong. It just doesn't make sense the the antiskid will not operate when the autobrake is active in RTO mode. And I don't see anything in the evidence you provided that says that the antiskid is inhibited when the autobrake is active in the RTO mode.

[BoeingBobby]

For what is worth, I have to side on Evan's and 3WE side here.

I have no specific information about how any specific antiskid and/or autobrake system works in any specific airplane type.

But I do have a general idea of the general concepts involved in designing and operating these systems in general, and I don;t see any reason why the antiskid would not operate in parallel with the autobrakes in any mode. In particular:

- I don't see any reason why, from an airplane operation point of view, it would be undesirable that the antiskid operates together with the antiskid in any mode including MAX and RTO. Rather the contrary. Skidding worsens (lengthens) the stopping distance, kills directional control, and at any med to high speed almost guarantees the destruction of the tires during the roll out, and possibly the damage of many other components in the landing gear assembly (it does prevent brake wear, though). On the other hand, a working antiskid guarantees the minimum stopping distance, keeps the directional control intact, and maximizes the possibility that the tires remains inflated until the plane stops (then the fuse plugs are likely to melt and deflate the tires, but the plane is already stopped).

- I don't see any technical reason that would make it difficult, economically unfeasible, unsafe or unreliable for the antiskid to work together with the autobrakes in any mode, including MAX and RTO. On the contrary, it would be simpler and cheaper to have the antiskid work in "its own world" regardless of and even ignoring whether the autobrakes are in mode MAX, RTO, 1, 2, or any, or even if it is the pilot feet or the autobrake who is actuating the brake.

BB, I cannot say for sure, but my engineering intuition (which is not infallible) tells me that this time you are wrong. It just doesn't make sense the the antiskid will not operate when the autobrake is active in RTO mode. And I don't see anything in the evidence you provided that says that the antiskid is inhibited when the autobrake is active in the RTO mode.

A: Re-read the anti-skid section of the FCOM. B: I have asked 2 check airman and another line Captain that is still on the line and they have all confirmed what I remembered.

[Evan]

- I don't see any reason why, from an airplane operation point of view, it would be undesirable that the antiskid operates together with the antiskid in any mode including MAX and RTO. Rather the contrary. Skidding worsens (lengthens) the stopping distance, kills directional control, and at any med to high speed almost guarantees the destruction of the tires during the roll out, and possibly the damage of many other components in the landing gear assembly.

Not to mention damage to the wing tanks from tire shrapnel.

Here's where we are: Intuition tells us BoeingBobby is wrong. But the line in the FCOM he posted about IRS seems to support his argument. There is nothing in any of the technical docs I have that mentions the relationship between RTO autobrakes and antiskid (which tends to go against BoeingBobby, since antiskid is a default system providing protections that pilots would assume are present unless the inop light is lit). The antiskid system is entirely "in its own world" downstream of the autobrake metering valves so there is nothing that prevents it being used with the RTO setting. It is possible that logic disables it, but I can't imagine why.

Intuitively, the only thing I can conceive in favor of his argument is that engineers tested RTO without antiskid in slick runway conditions and found that it still stopped in a shorter distance, but that goes against physics... and controllability...

I seem to remember a documentary of certification of airliners where the 'worst case scenario' brake test was conducted from high speed with antiskid deactivated, and when the aircraft stops the tires are deflated and on fire.

[BoeingBobby]

Not to mention damage to the wing tanks from tire shrapnel.

Here's where we are: Intuition tells us BoeingBobby is wrong. But the line in the FCOM he posted about IRS seems to support his argument. There is nothing in any of the technical docs I have that mentions the relationship between RTO autobrakes and antiskid (which tends to go against BoeingBobby, since antiskid is a default system providing protections that pilots would assume are present unless the inop light is lit). The antiskid system is entirely "in its own world" downstream of the autobrake metering valves so there is nothing that prevents it being used with the RTO setting. It is possible that logic disables it, but I can't imagine why.

Intuitively, the only thing I can conceive in favor of his argument is that engineers tested RTO without antiskid in slick runway conditions and found that it still stopped in a shorter distance, but that goes against physics... and controllability...

I seem to remember a documentary of certification of airliners where the 'worst case scenario' brake test was conducted from high speed with antiskid deactivated, and when the aircraft stops the tires are deflated and on fire.

For Christ's sake, I posted a video of it yesterday. I am done with this one. Gabe, I have the Sim all set for your visit.

[3WE]

To be honest I think it’s time to close this thread. We have one real life heavy driver giving the chapter and verse on how it all works versus, at best a bunch of flight sim drivers.

Bold font = an unresolved issue, and the reason the thread should NOT_be closed. (Side note: ATL crew is correct that many other threads should be closed if flight simmers are debating pilots).

Most modern cars have ABS.

Most airliners have ABS.

ABS is available most of the time on an airliner.

ABS generally improves braking performance and controllability.

An aborted takeoff is a time when we flight simmers think you need some pretty good braking. (Do Bobby & ATL disconcur with this?)

Unresolved: With ABS doing sooo many good things, is it really NOT available during a rejected takeoff?...especially on a rainy or snowy day?...really?...really really?

I concur that Bobby doesn't need to know that, but as a seasoned operator of 747's and Piper cubs and possibly an El Camino or two, I'd think he might have some insight here- other than barfing back stuff from the manual and check pilot communications that say no ABS...

I also concur that maybe this question should go to some Boeing Aeroengineers and not_an experienced autopilot monitorer.

Nevertheless, the why is still missing from this discussion.

By the way (and this is parlour talking out my butt), during a rejected takeoff, a 747 is going to tend to be heavy, thus you'd have excellent tire-runway traction and maybe not_need ABS...then again is it sooooo heavy that even snow or ungrooved runways won't matter?

[3WE]

https://www.youtube.com/watch?reload=9&v=_g6UswiRCF0

Ironically, this video says, "The pilot slammed on the brakes"

The very wording that brought Bobby here to tell us was wrong...that the RTO automatic braking system does it.

Should we assume that this video is wrong?

[3WE]

I seem to remember a documentary of certification of airliners where the 'worst case scenario' brake test was conducted from high speed with antiskid deactivated, and when the aircraft stops the tires are deflated and on fire.

The one with the tire fire was an Airbus. [I am 100% serious].

Switching to typical crap stirring humour (while still being accurate), this stimulated much chatter from the Anti-Composite-FBW bunch on various aviation-parlour-talk fora.

[Evan]

For Christ's sake, I posted a video of it yesterday.

In your video the aircraft stops with the tires inflated and not on fire. The tires deflate only after the brake heat convects through the rims and the fuse plugs take effect. This is, of course, by design, to maintain control while rolling but then to prevent tire explosion when stopped. I will try to find the video I was referring to.

[BoeingBobby]

Same here.

Can you tell us how the RTO brakes work in the Bus please? And I know, very well. LOL