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

[Evan]

...Maybe upstream from some brake-by-wire system there's 3000 PSI

Yes, it's called accumulator pressure. I think he's talking about accumulator pressure (max is 3500psi BTW):

[BoeingBobby]

I give up! The brake system in the airplane that I flew for 18 years is 3000 psi. There is NO "brake by wire" system even in the brand new -8. As far as what is in the 737, I have no fucking idea, and now I really don't fucking care either.

This is out of the FCOM so believe what ever you like.

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.

The Parking brake accumulator (normal brake accumulator) is located in hydraulic system 4 and provides emergency brake
pressure to set the Parking brake if the normal and alternate brakes are inoperative. The Parking brake accumulator pressure
is for setting the parking brake only and cannot stop the aircraft.
 The HYD BRAKE PRESS gauge located on the Captain’s panel shows the brake pressure measured at the accumulator.
 When the Parking brake is set:
 The Parking brake valve (located in the brake return line) is closed, trapping brake pressure.
 The brake pedals are mechanically locked down.
 When the Parking brake is released:
 The Parking brake valve is opened releasing the brake pressure to the brake return line.
 The brake pedals are released.

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.

[Evan]

This seems wrong...I would think that the brake pressure would vary some with the traction/speed/lift/weight/surface conditions?

Ah, ok.... With the autobrakes in RTO and the antiskid active, the system is afforded maximum pressure (3000psi+) but the brake pressure is modulated by a pressure bias modulator circuit, so if the wheel sensors tell the control unit the the a/c is entering a skid (comparing a/c velocity with wheel speed) it WILL reduce the brake pressure. The system bypasses the manual braking, using the summing amplifier voltage level to control brake pressure and is thus, I suppose, what you could call brake-by-wire. Or unbrake-by-wire is perhaps more accurate... So RTO is giving full available pressure UNLESS a skid is imminent, thus the maximum effective braking under control. So it's not 3000psi no matter what, but I don't think BoeingBobby ever said that.

[BoeingBobby]

Ah, ok.... With the autobrakes in RTO and the antiskid active, the system is afforded maximum pressure (3000psi+) but the brake pressure is modulated by a pressure bias modulator circuit, so if the wheel sensors tell the control unit the the a/c is entering a skid (comparing a/c velocity with wheel speed) it WILL reduce the brake pressure. The system bypasses the manual braking, using the summing amplifier voltage level to control brake pressure and is thus, I suppose, what you could call brake-by-wire. Or unbrake-by-wire is perhaps more accurate... So RTO is giving full available pressure UNLESS a skid is imminent, thus the maximum effective braking under control. So it's not 3000psi no matter what, but I don't think BoeingBobby ever said that.

You see anything in the anti-skid section on RTO? No, you know why? Because on RTO it is 3000 psi to all 16 brakes right now. No anti-skid, no wires, just good old Skydrol!

[Evan]

You see anything in the anti-skid section on RTO? No, you know why? Because on RTO it is 3000 psi to all 16 brakes right now. No anti-skid, no wires, just good old Skydrol!

You can't be serious. RTO is when you need anto-skid the most. In fact, I think autobrake is inop on the 737 if antiskid is inop. Autobrake is just another metering valve upstream of the antiskid valves, so there is no reason why antiskid would not be available with RTO. It would also be sort of insane, since skidding can PROLONG stopping distance not to mention the loss of directional control. If you want 3000psi to all brakes now, you have to switch off the antiskid and stand on the brake pedals, and then, uh, brace...

[BoeingBobby]

You can't be serious. RTO is when you need anto-skid the most. In fact, I think autobrake is inop on the 737 if antiskid is inop. Autobrake is just another metering valve upstream of the antiskid valves, so there is no reason why antiskid would not be available with RTO. It would also be sort of insane, since skidding can PROLONG stopping distance not to mention the loss of directional control. If you want 3000psi to all brakes now, you have to switch off the antiskid and stand on the brake pedals, and then, uh, brace...

You keep talking about anti-skid. It is not involved with RTO braking. That is why I included the anti-skid section for you. Do you see RTO mentioned in the anti-skid section one time? Yes if the ant-skid is DMI'd the will be no AUTO-BRAKES, but you will still have RTO brakes. Again I have no idea if this holds true on a 73.

[Evan]

Do you see RTO mentioned in the anti-skid section one time?

No, but it certainly would be if what you are saying was true. But think about what you are saying. The main difference between MAX autobrake and RTO are the means of activation. Both are there for workload reduction, but MAX applies 3000psi while transitioning to ground mode (main gear sensors). RTO applies it after thrust reaches idle (lever sensors). There are both acting on the metering of pressure upstream of the anti-skid valves. They can both take full advantage of them. Now, what would be the rationale for defeating antiskid in the RTO mode? (remember, RTO ONLY activates in the high-speed (>80kts) regime). The airplane can sense its deceleration (IRS) and individual wheel speed (wheel sensors) but it can't sense runway conditions, and very often runway conditions are such that simply clamping down the brakes with full force would result in skid, extended stopping distance and runway excursion. The antiskid can detect a skid before it happens; a pilot often can't detect one until well after it happens.

It's perfectly understandable how a million-hour veteran like you would not have perfect understanding of RTO autobraking since it is possible to have all those hours without ever needing it, but I would run that by your check pilot friend again...

(BTW, AFAIK, the autobrake was first developed for the B737)

[3WE]

...RTO is when you need anto-skid the most...It would also be sort of insane, since skidding can PROLONG stopping distance not to mention the loss of directional control...

Remember my assertation that it is sometimes possible to train sooooo much on procedures that important, really basic stuff can suffer.

Wet or dry...grooved or not...the pressure in a hose is on this particular model is 3000 PSI...as to what effect locking the wheels has (on bicycles OR 172s OR 747s)...not important.

Someone also recently said, "Steep banks are done at 10,000 Feet, 250 knots and 45 degrees". Anyone wanna guess why that comment bugged me (Gabe?)

[BoeingBobby]

(BTW, AFAIK, the autobrake was first developed for the B737)

I have no idea, I have never been anything but a passenger on a 73

[BoeingBobby]

Someone also recently said, "Steep banks are done at 10,000 Feet, 250 knots and 45 degrees". Anyone wanna guess why that comment bugged me?

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

[BoeingBobby]

RTO autobraking since it is possible to have all those hours without ever needing it, but I would run that by your check pilot friend again

Never personally had a reject that fast except in the Sim. I have however 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!

[BoeingBobby]

The airplane can sense its deceleration (IRS) and individual wheel speed (wheel sensors)

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.

[Evan]

Never personally had a reject that fast except in the Sim. I have however 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!

I would assume that is the result of excessive brake heating transferred to the fuse plugs. Anti-skid isn't there to keep things cool, it is there to keep things controllable and to stop in the shortest possible distance for all runway conditions. Since it is active by default, the only way it would not be involved is if the RTO logic deactivates it, and that just goes against common sense...

[BoeingBobby]

I would assume that is the result of excessive brake heating transferred to the fuse plugs. Anti-skid isn't there to keep things cool, it is there to keep things controllable and to stop in the shortest possible distance for all runway conditions. Since it is active by default, the only way it would not be involved is if the RTO logic deactivates it, and that just goes against common sense...

Then I highly recommend that you call the Boeing Company and bitch at their engineers, being that you seem to know more than they do. Don't blow your fingers off today with fireworks!

[3WE]

Then I highly recommend that you call the Boeing Company and bitch at their engineers, being that you seem to know more than they do. Don't blow your fingers off today with fireworks!

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)