RTO and brakes - 757/767

[britannia66]

If a take off is rejected and RTO brings the aircraft to a halt, does the brake remain set on the Boeing 757/767?
Also, where is the technical reference for the answer? :ugh::ugh::ugh:

[None]

Reference Vol II page 14.20.6, the autobrakes disarm for the following:

F fault in the system

S SB lever moved to the down detent after being deployed

T thrust lever (either) advanced after landing

O Off or Disarm is selected on the autobrakes selector

P pedal pressure is applied

[britannia66]

I can see nothing in my company manual that confirms the brake REMAINS set sfter the aircraft has come to a halt. It confirms that "autobrakes bring the a/c to a halt". I am thinking of the evacuation scenario, when engines will be shut down etc. etc.

[Right Way Up]

britannia66,
I believe none has given you the answer!

[RAT 5]

B66:

Does your question hint at whether the park brake needs to be set after an RTO? T
There is always a debate about whether to set the park brake after a high speed RTO in case of brake seizure. All airlines I have worked for had an SOP of "set park brake and analyse." In doing so you will apply pedal pressure and so disarm the autobrakes.
Some airlines retract the spoilers with a/c stopped, others do only if an evac is required. The former would disarm the autobrakes.

[None]

If you are going to evacuate, Boeing says to set the parking brake. If you are not going to evacuate, Boeing says to consider not setting the parking brake.
All is in the QRH.

[britannia66]

Thank you all for your replies ... no-one however has answered my question. If you use RTO, and do NOTHING else, does the brake remain set? QRHs all differ, as do company manuals!
Do the brakes remain set .... yes/no?

[Fil]

See the first reply to your question! A reference is even provided.

[cambridge]

My company's Volume 2 certainly does NOT answer the direct question asked! If no other action is taken, do the brakes remain set?

[Spanner Turner]

If a take off is rejected and RTO brings the aircraft to a halt, does the brake remain set on the Boeing 757/767?

Yeah, the brakes remain set. This was answered in post 3 - with the handy FSTOP acronym. I've pasted the relevant text highlighted in green below. Also below are the arming, application and disarming criteria of the brakes and of the autobrake selector switch.


RTO Autobrake Arm
The autobrake system ARMs when in the RTO mode and latches the
selector when:
• The RTO mode is selected.
• There is no autobrake malfunctions.
• Both air/ground systems indicate ground mode.


RTO Autobrake Application
Autobrake application in the RTO mode applies full system pressure
to the antiskid valves when the following criteria are met:
• All thrust lever switches indicate retarded.
• Average wheel speed has exceeded 85 knots and currently > 80
knots.
• Pedal brake pressure < 500 psi on aircraft with carbon brakes (<
750 psi on aircraft with steel brakes).


Full pressure is applied until removed by any of the following
conditions:
• RTO selected OFF.
• Any thrust lever switch indicates advanced.
• Either brake pressure switch on the shuttle valves, indicates high
pressure. ( Pressing on the brake pedals.)
• Antiskid/autobrake fault detected.
• Speed brake handle stowed after being extended during or after
autobrake application.


The autobrake system remains latched in the RTO position until one
of the following occurs:
• Selector switch is placed to OFF.
• At least one air/ground signal indicates air mode.
• There is a loss of autobrake power.

NOTE:
A fault occurring when RTO is selected, will only
illuminate the fault light and display an EICAS message.
The selector will remain latched in the RTO position.


Also, where is the technical reference for the answer?


Boeing Aircraft Maint Engineers Training notes. (Yeah, they teach us all the nitty gritty stuff - anything else you want/need to know?) :ok:

[Kit d'Rection KG]

Whilst I'm very dubious why the question is even being asked in the first place - as I can perceive no operational reason to ask it, I'll offer the following...

If you don't de-power the aircraft (eg by the evacuation checklist), the autobrakes will remain set at RTO (but in a low speed mode without protections).

If you do de-power the aircraft (and I can't remember nor be bothered to look up the source for the autobrakes), then you'll satisfy the 'f' criterion above and the brakes will dis-engage. :rolleyes:

Why not just do the right thing and set the parking brake when the aircraft stops? :cool:

Thomson66, perhaps you'd tell us why you're asking? :ok:

[None]

"What's the technical objection in setting the park brake at the end of an RTO & releasing it if it is decided to taxi clear?"

That may be an excellent technique most of the time. Perhaps Boeing does not want to mandate that a pilot shall set the parking brake at the end of every RTO. In other words, it might not be the best thing to do in all scenarios, so they let us decide. This is just my take on it...I'm no expert, and certainly not a lawyer.

Back to the technical questions, here is some more info:
The AMM does not say if the system brings the aircraft to a complete stop, however it also does not say that the system releases the brakes nearing full stop.

If the airplane speed drops below 7.5 knots, the system provides no brake release for the antiskid signal.

In addition to the F-STOP items, the RTO is disarmed when one of the air/ground signals shows the air mode (Power is removed from the latch, and the switch turns to the OFF position). This is what you see after takeoff.

"Backtrack" has provided information from the sim. That is very helpful, however I have seen things in the jet that the sim did not show.

[britannia66]

Back Track ... you guess right!
Spanner Turner ... thank you for such a clear reply (the only one). Be a little forgiving though! ... we mere pilots do not have access to the engineering manuals. Thanks again.

[Spanner Turner]

I shall try to answer/comment on a few things mentioned in previous posts,

Backtrack said:-

As I understand the system, setting the park brake closes a valve in the return lines, thereby trapping fluid (pumped at 3,000psi) between the brake units & the hyd reservoirs. This makes obvious sense for when the a/c becomes depowered as there will be no pressure in the normal lines & without this trapped fluid, the a/c could move.

For all intents and purposes, pretty well spot on the money with the above.

Backtrack also said:-

Because Boeing's QRH drill recommendation is to only 'consider setting the park brake if an evacuation becomes necessary.' ( I've paraphrased this last bit from the QRH).

What I don't understand is why Boeing don't feel this is a requirement at the end of an RTO. The first item on the new, by reference, evacuation checklist is to set the park brake. Why only now? What's the technical objection in setting the park brake at the end of an RTO & releasing it if it is decided to taxi clear?

Spanner Turner
Do you have an expert's view on this?

Okay, I’m now stepping out of my territory (i.e I’m not a pilot, don’t have access to your QRH or SOP’s and am only commenting as I’ve been asked to and based on my previous experience in dealing with the aftermath of RTO’s)

What I don't understand is why Boeing don't feel this is a requirement at the end of an RTO.

Could I venture a guess (a second guess at that) as to why Mister Boeing has come up with this?

I think the point here is that there is a BIG difference between an RTO and an Evacuation. Not every RTO ends in an evacuation. A “Rejected Take-off” is just that, a decision made after commencing the take-off roll that the take-off should not be continued. The reasons for this decision are many I’m sure you’ll agree. The decision alone to abort a take-off in no way implies that the passengers/crew are in danger and need to be evacuated, it doesn’t even suggest the aircraft was incapable of flight, it purely means that the pilot has decided that it be prudent to abort and slow down/stop the aircraft.

Some of the reasons for aborted take-offs I’ve seen in the Tech Log are;
Cargo door light illuminated during roll.
Capt’s #2 window handle moved from ‘Lock” to ‘Open’ during roll.
Nearby aircraft on taxiway reported ldg gear pin streamer visible on the Tower frequency
Extreme nosewheel vibration.
Runway incursion by ‘Safety’ vehicle.
Runway incursion by other aircraft.
Captains Mother calls the Tower to say that ‘Little Johnny’ has forgotten his lunch.
My fleet also has a bad history of Engine ‘Bleed’ defects on the 767 causing RTO’s.

In all the above instances I’ve never heard of my flight crew actually letting the aircraft come to a complete stop under autobraking and wanting to “Park” the brakes on the active strip. In reality, the defect is noticed, decision made to reject, thrust levers retarded, autobrakes apply, the aircraft speed is slowed down via autobrakes, whereupon manual braking is applied (like a normal landing) which disarms the autobrakes, and the aircraft vacates the runway.


The first item on the new, by reference, evacuation checklist is to set the park brake. Why only now?

As above, the difference here is that you are “evacuating” the aircraft. This MAY be after an RTO, but it may just be after you’ve taxied out of the ramp. If you’ve decided that all the SLF need to try their luck down the slippery slides then it is best that you set the Park Brake. This stops the aircraft from moving as the victims hurtle down the chutes towards the unforgiving tarmac. (It also stops some nasty abrasion on the underside of the slide)


What's the technical objection in setting the park brake at the end of an RTO & releasing it if it is decided to taxi clear?

I’m sure there’s no technical objection. If a cargo door light comes on on your next take-off roll (or dear old Mum calls to say you’ve forgotten lunch) and you decide to abort, I’d say you’d be quite within your rights as Captain to come to a complete halt on the strip and to set your Parking Brake before deciding the next course of action.


None said,

Back to the technical questions, here is some more info:
The AMM does not say if the system brings the aircraft to a complete stop, however it also does not say that the system releases the brakes nearing full stop.

If you have a look at my post #11, on more than one occasion are the following words

"Autobrake application in the RTO mode applies full system pressure."

Just like your car, if you supply “Full system” pressure to the brakes, by default the aircraft will come to a complete stop. (Ideally before hitting an immovable object)


None said,
If the airplane speed drops below 7.5 knots, the system provides no brake release for the antiskid signal.

This is 100% true. If there was no low speed drop out then the aircraft would never come to a complete halt as the anti-skid would see the wheels as locked and release pressure from the brakes.
In reality this means that when IRS speed falls below 7.5kts, the wheels may lock-up depending upon pressure supplied.

None said,

In addition to the F-STOP items, the RTO is disarmed when one of the air/ground signals shows the air mode (Power is removed from the latch, and the switch turns to the OFF position). This is what you see after takeoff.

Well no actually, see post #11, RTO is disarmed for the reasons listed

The autobrake system remains latched in the RTO position until oneof the following occurs:
• Selector switch is placed to OFF.
• At least one air/ground signal indicates air mode.
• There is a loss of autobrake power.

The fstop items are ones that ‘release’ the braking pressure – not disarm the RTO.




Spanner Turner ... thank you for such a clear reply. Be a little forgiving though! ... we mere pilots do not have access to the engineering manuals.

That may be true my friend, but us mere engineers don’t have access to bright shiny aluminium tubes that can soar through the skies and in a few small hours, transport oneself to far-off exotic locales and new worlds of undiscovered bars, pubs and nightclubs and experiences.
During my 'workday' I venture no more than 5 Nm from my home.

Boring.

[RAT 5]

S.T. Good post and from my stand point all well said.

The only reason I've heard about not setting Pk Bk after a high speed RTO was tyre fuse flug blow out, possibly gluing the brakes on, and brake fire because of high temps. I do not know enough about modern brake systems versus old ones. Is this idea of heat-gluing the brakes or blowing the plugs and old wives' tale left over from older technologies? What about fire risk?

I was once checked out in the sim by a TRE from another country's airline. He was amazed I set the brakes when lined up, but not yet cleared for takeoff. His SOP, personal or operator I do not know, was to hold on the foot brakes in case they stuck on and you blocked the runway. Hm! I suppose anything could go wrong: but this?? If he thought they could stick after just taxing, then what about a high speed RTO? He'd just set the brakes at the holding point and they released then; how can another 50m make any difference?

[Basil]

RAT 5,
I think the reason for not setting the park brake when lined up is to cover the unlikely case of a mechanical failure preventing release.

[None]

"The fstop items are ones that ‘release’ the braking pressure – not disarm the RTO. "

Fair enough...I stand corrected. After takeoff, the ABS will no longer be latched in the RTO position due to the above.

One of the reasons (there are other reasons) some train to not set the parking brake when lining up to wait is because of this high profile accident:

http://www.airdisaster.com/reports/ntsb/AAR81-06.pdf

The National Transportation Safety Board determines that the probable cause Of the accident was the flightcrew's failure to release the parking brake before the takeoff roll was started, which resulted in significant wheellbrake drag and a nosedown pitching moment that inhibited the aircraft's capability to effect a normal acceleration and rotation for takeoff.

[typhoid]

The reason for not setting the park brake following an RTO (and we are really talking quite high KE not a low speed abort) is to prevent the hydraulic thermal fuses from blowing which prevents overpressure in the park brake hydraulic lines.

As a previous poster has said when the pb is on the return line is isolated and 3000psi is trapped at the wheels.

A secondary reason is the paranoia that the brakes will seize due to high temps and not release on selection.

Also not setting the brakes allows air to get between the rotors and stators and cool everything much quicker. My experience from RTO Flight Testing is that brake temps can continue to rise by up to 50 degs C with the brakes still applied vs immediate cooling with them released - less chance of fusible plugs blowing.

[Kit d'Rection KG]

No. :)

There is no circulation of hydraulic fluid if the brakes are pressurised, the cooling issue is to do with whether the brakes are ON or not, as expounded earlier in this thread. :bored:

My original response reflected my concern that one day, perhaps soon, we'll see a crew come to a stop after an RTO, then not set the parking brake, then do something (spot that the autobrake switch is at RTO, and switch it off, or de-power the aircraft), for the aircraft to roll unbraked into the next obstacle downhill and/or downwind of it. Thus, once again, a trained flight crew (Boeing's words, not mine) will snatch defeat from the jaws of victory, and probably end up on the front page of a tabloid and/or in the fleet manager's office (perhaps simultaneously). :ugh:

This response reflects a concern that it's now possible to be an instructor or examiner with very little technical knowledge of the aircraft's systems - or system design in general. :(

[Kit d'Rection KG]

...and fundamentally, as an aircraft commander, if I'm stopped on the ground, and I'm not just about to go anywhere, I'll set the brakes so that the above doesn't happen to me. :)

I might think about getting some chocks inserted and taking care of things that way, but leaving the aircraft restrained by the autobrake after an RTO is a complete no-no in my book, and will remain so until someone brings forward a convincing argument as to why that action would amount to good airmanship. :rolleyes:

I fear that this is another case of a manufacturer's poorly-thought-through procedure being deconstructed by anally-retentive trainers who can't see the wood for the trees. ;)

Sorry for the harsh words, but you may have guessed, that they're heartfelt. :*

[RAT 5]

Good point about the possibility of the a/c being unrestrained and rolling forward whilst the crew's attentions is quite rightly focused inside on what the hell happened.

Further, I see so many times in the sim that, contrary to Boeing's ideal world, a significant number of pilots disarm the autobrakes with their feet in the stress of the RTO, thus rendering the SOP of not setting the parking brake because the RTO will keep the a/c safe as non- effective.

[Yon Garde]

Found a very illuminating video on YouTube that visually demonstates what actually happens in a high speed, high weight RTO.

From the test, I would imagine that a reject at or near V1 at a high weight would guarantee the brakes welding assuming steel brakes on many jet transport types.

Good discussion topic, keep it coming.
www.youtube.com/watch?v=l5N2uBqJbVU

[Kit d'Rection KG]

"Cashman and his crew would be sitting on a potential timebomb" :yuk:

"...the plane could survive almost intact" :yuk::yuk:

A very unremarkable video of a very routine test.

[Shore Guy]

The RTO video that was truly entertaining was the A-340 one that was pulled off the web by Airbus.
If anyone has another link (I think it was on YouTube) for that video, please post. They almost lost the airplane on that one.