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

[Evan]

Please show me in Vnav's post where he says ANYTHING about RTO being less then max pressure.

As you mentioned, the RTO portion provides straight up max pressure while the 4 levels of Landing autobrakes will shoot for a predetermined deceleration rate and the max landing setting is still less than the RTO setting. However, I have to believe that they're all also governed by the antiskid system or else they all become worthless when you shred tires.

Max pressure to the anti-skid valves; modulated pressure (if an imminent skid is detected) to the brakes. So you are right unless (you are wrong).

[Gabriel]

But the line in the FCOM he posted about IRS seems to support his argument.

I don't think so (again, no hard proof yet)

In modes 1, 2, 3, 4 and MAX there is a threshold brake pressure and a target deceleration. (I have just learned that MAX is not maximum possible but maximum setting, and that maximum manual brake can provide more deceleration if there is enough traction with the runway).

The logic is that, in these modes, the autobrake will provide enough brake pressure to meet the target deceleration (how much pressure is needed for that depends on airplane weight, reversers setting, spoilers, runway slope, since the more deceleration caused by other means the less braking action needed to meet the target deceleration), but it will not exceed the threshold pressure for each mode, and if a wheel locks the antiskid will relieve pressure on that wheel even if the target deceleration has not been met (that means that if in a particular landing the deceleration in say mode 3 cannot reach the target because is limited by skidding, then mode 4 or max will not provide any additional braking).

But according to what I found in a Boeing 747-400 FCOM and a FCTM that I found on line (that in a part said exactly the same than BB posted), it seems that the IRS is used to measure the deceleration against the target and NOT for antiskid purposes, that's why the IRS is not used in RTO mode, there is no target deceleration there, it seems to be max pressure, I understand (although it was not stated) that only limited by antiskid.

In another less reliable publication I found that, once the airplane is in GORUND mode and the wheels have spun up, the antiskid works by comparing the speed of the different wheels.

[Gabriel]

you have to also placard the Autobrake system for takeoff and landing as inop.

But is it ok to use it in other stages of the flight?

[Gabriel]

Because nothing does! I will say it again one last time for you. RTO brakes on, 3000 psi right now! As Vnav said as well by the way.

Again, I have no proof, but I believe that it does provide straight max pressure to the brake system but the antiskid can relieve pressure on individual wheels if it senses skidding (with the brake system at great still at 3000 PSI).
Yes, also in RTO.

[Gabriel]

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.

I did, I read with attention your posts, and I also researched online and found basically the same.

You are interpreting "Brake pressure is 3000 psi" and "Does not use IRS deceleration data" as equivalent to "No antiskid".

I am however confident (again, no hard proof) that "Brake pressure is 3000 psi" means that the brake system is pressurized to that pressure but that the antiskid still can and will relieve pressure on individual wheels if it senses skidding, and that "Does not use IRS deceleration data" is due to the fact that in RTO there is no deceleration goal to compare against the actual deceleration obtained from the IRS. It is max pressure and the deceleration will be what Physics will dictate (but with the antiskid still operative).

Autobrakes general.
 In the OFF position, the Autobrakes are not powered. CPAT online training 2015.
 Autobrakes utilize the IRS for pitch and deceleration purposes. For landings, each autobrake setting uses a fixed
deceleration rate in conjunction with IRS deceleration data.
 The Autobrake setting may be increased or decreased during landing rollout as necessary.
 Brake strength from greatest to least: RTO, max manual, MAX AUTO, 4 through 1.
 You do not have to out-brake the autobrakes when disarming them.
 The use of reverse thrust and/or speedbrakes will reduce the overall brake energy used.
 EICAS AUTOBRAKES: the autobrakes are disarmed or inoperative.
 RTO:
 Brake pressure is 3000 psi.
 Does not use IRS deceleration data.
 Brakes are activated if:
 Groundspeed > 85 knots.
 Thrust levers at idle.
 To disarm RTO brakes, use either method:
 Manually apply the brakes.
 Select the autobrake switch to OFF.

Anti-skid
 The anti-skid controller determines the anti-skid valve operation for each wheel brake.
 The anti-skid system prevents brake application prior to touchdown.
 The Brake Torque limiter prevents gear structural damage by signaling the anti-skid to release some brake pressure. This
occurs when high brake torque is sensed by an individual brake torque sensor on a wheel.
 With normal brakes, the brake torque limiter provides anti-skid (release of brake pressure) to the individual wheel.
 When alternate brakes are used, the brake torque limiter provides anti-skid (release of brake pressure) to wheel pairs
via the alternate anti-skid valves.
 Anti-skid is armed above 8 knots wheel speed on the ground.
 The anti-skid system operates if a wheel:
 Skids.
 Locks up during rollout.
 Hydroplanes.
 Does not spin up after touchdown.
 If a skid or locked wheel is detected during rollout, the anti-skid reduces brake pressure on that wheel.
 During wheel hydroplaning or if a wheel does not spin at touchdown, the groundspeed is greater than the wheel speed. All
brakes are released.
 The EICAS message ANTISKID means a loss of anti-skid on one or more wheel brakes.
 The EICAS message ANTISKID OFF means either:
 The Parking brake valve is not fully opened while the parking brake is released.
 Power failure of the Brake system control unit.

[Gabriel]

Gabe, I have the Sim all set for your visit.

Amazing!!!

[Gabriel]

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.

Hey, correcting you just because it is the second time. I don't believe that convection is the right process here. It would be conduction. Convection is the transportation of heat by transporting hot material to a colder place. Conduction is the transportation of heat by one hot molecule transferring heat to the colder molecule next to it, and the next, and the next... So unless you have hotter parts of the rim near the brakes moving to colder zones near the tire, this is not convection but conduction. In other words, for convection you need large scale movement (typically of a fluid), such as provided by a fan (forced convection) or by the density/buoyancy of different zones of the fluid with different temperatures (natural convection). When you touch a hot something and you burn your finger, that is conduction.

[ATLcrew]

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

The 'Bus (at least the A320 family) is a bit different in that we don't have as many Autobrake settings as you Boeing folk. In fact, we only have three, Low, Med, and Max. Max is authorized (and required) only for Takeoff (in fact, it won't arm with weight-off-wheels) and yes, antiskid is used for Max as well, but it bears remembering that antiskid on the A320 family disarms below 20kts groundspeed, regardless of what the brakes are doing. Another things that bears remembering is that autobrakes will not activate for an RTO if the aircraft never makes it past 72kts groundspeed. This is because autobrakes are activated by ground spoiler deployment, and said spoilers will not deploy below that speed.

[Evan]

Hey, correcting you just because it is the second time. I don't believe that convection is the right process here. It would be conduction. Convection is the transportation of heat by transporting hot material to a colder place. Conduction is the transportation of heat by one hot molecule transferring heat to the colder molecule next to it, and the next, and the next... So unless you have hotter parts of the rim near the brakes moving to colder zones near the tire, this is not convection but conduction. In other words, for convection you need large scale movement (typically of a fluid), such as provided by a fan (forced convection) or by the density/buoyancy of different zones of the fluid with different temperatures (natural convection). When you touch a hot something and you burn your finger, that is conduction.

Ugh, my bad Mr. White.. indeed the fuse plugs fail from conductive heat, but isn't the heating of gas inside the tire, the reason the fuse plugs exist in the first place and thus the real issue, convection?

[3WE]

Hey, correcting you just because it is the second time. I don't believe that convection is the right process here. It would be conduction. Convection is the transportation of heat by transporting hot material to a colder place. Conduction is the transportation of heat by one hot molecule transferring heat to the colder molecule next to it, and the next, and the next... So unless you have hotter parts of the rim near the brakes moving to colder zones near the tire, this is not convection but conduction. In other words, for convection you need large scale movement (typically of a fluid), such as provided by a fan (forced convection) or by the density/buoyancy of different zones of the fluid with different temperatures (natural convection). When you touch a hot something and you burn your finger, that is conduction.

With beautiful bright orange brakes and black rubber tires a foot? apart, should we consider radiation transfer too?

[Gabriel]

For sure there is conduction, convection and radiation. But not "heat convects through the rims"

[3WE]

But not "heat convects through the rims"

Unless the rims were really really really hot, really really melted and not particularly viscous...

[flashcrash]

I have seen the real thing happen more than once. Usually ends up with 14-16 blown tires, you know why? BECAUSE THE ANTI-SKID SYSTEM IS NOT INVOLVED!

Respectfully: not correct. On the 747 the anti-skid system must be ON with no faults for auto max braking to be applied during an RTO.

[BoeingBobby]

So when you are wrong, you admit you are. I was wrong! I received an email from an ex Flight Engineer of mine that went to work for Boeing when Atlas retired all of our 200’s and 300’s. He and his crew maintain both Air Force One VC-25A’s, and all of the Air Force E-4’s in San Antonio, Texas.

If the Anti-Skid is out, so are the RTO brakes, as well as all of the normal auto-brake systems.
However, I was correct in the fact that RTO commands full brake hydraulic system pressure of 3000 psi to all 16 main gear brakes. If a skid is detected, the anti-skid will release the individual wheel. When the wheel spins back up, 3000 psi again!

Now to make a bunch of you jealous. Gabe will get to show me how he can visually land the 747/200 simulator next month. I have arranged for him to fly our simulator that we train all of the Air Force One and E-4 pilot’s in.

[Evan]

Now to make a bunch of you jealous. Gabe will get to show me how he can visually land the 747/200 simulator next month. I have arranged for him to fly our simulator that we train all of the Air Force One and E-4 pilot’s in.

WIth or without STALL protection...