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Can Anybody Explain "Autobrake" - Quick!  
User currently offlineBlackened From , joined Dec 1969, posts, RR:
Posted (12 years 9 months 5 days 1 hour ago) and read 1384 times:

I know this might be in the wrong forum but the tech forum isn't that busy right now but I need to know it fast.
What is the autobrake function of an aircraft and does it work exactly. I'm sure some of you know.

16 replies: All unread, jump to last
 
User currently offlineSpitfire From France, joined Feb 2001, 801 posts, RR: 7
Reply 1, posted (12 years 9 months 5 days 1 hour ago) and read 1343 times:

As soon as there are wheels spinup on landing, hydraulic pressure (around 1000psi) is applied to the brakes, in order to maintain a constant deceleration choosen by the pilot (minimum, medium and maximum) without pushing on the brakes pedals (on the rudder pedals). This is of course done through the antiskid ( antilock or ABS) system in order to keep the wheels spinning. It's very usefull especially with very strong cross-wind, slippery runways or during a CAT III landing, in order to stop the plane in a minimum of time.
Hope it helps.
Sptfire



Sabena ... Never to be forgotten (12 years already , what a shame !! )
User currently offlineTG992 From New Zealand, joined Jan 2001, 2910 posts, RR: 10
Reply 2, posted (12 years 9 months 5 days 1 hour ago) and read 1326 times:

Surely the name would give you a clue?



-
User currently offline777236ER From , joined Dec 1969, posts, RR:
Reply 3, posted (12 years 9 months 5 days 1 hour ago) and read 1311 times:

It's a brake, that's automatic. It brakes the aircraft......automatically. Hence the name, "Auto..." um "..brake"

Want me to simplify?


User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 4, posted (12 years 9 months 5 days ago) and read 1305 times:

"in order to stop the plane in a minimum of time."

A common misconception about the Autobrake, it does not stop the aircraft in the minimum time. Even maximum autobrake does not provide the level of retardation supplied by full, manual braking.

The benefits of the autobrake system are that it provides optimum anti-skid operation, it allows smooth, timely and even braking irrespective of pilot workload and it maintains uniform braking even during rudder inputs (i.e. crosswind landing benefit).

It is never used to stop very quickly, the best way to do this is the good old-fashioned "slam on the brakes"!



I used to love the smell of Jet-A in the morning...
User currently offlineSpitfire From France, joined Feb 2001, 801 posts, RR: 7
Reply 5, posted (12 years 9 months 4 days 13 hours ago) and read 1249 times:

Rick767,

You are right. To prove that we just have to look at the braking charts in our different AOM. With autobrake the stop distances are longer.
I only tried to make it quick and simple..."Autobrake for dummies..."  Wink/being sarcastic
Thanks for the correction.
Spitfire



Sabena ... Never to be forgotten (12 years already , what a shame !! )
User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 6, posted (12 years 9 months 4 days 12 hours ago) and read 1224 times:

What's your thoughts on autobrake stopping capability in regard to "MAX", "RTO" or other selectable modes depending on manufacturer or a/c type designed to send maximum hydraulic pressure to brake system (modulated by antiskid of course). This I thought was akin to "slamming the brakes".


You're only as good as your last departure.
User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 7, posted (12 years 9 months 4 days 10 hours ago) and read 1192 times:

Also, the stopping power (in land mode) in "MAX" and stopping distance might be deceiving.

During landing using "MAX" ABS, there is normally a time delay before the pressure is sent to the brake system which would increase stopping distance.

But the hydraulic pressure IS at its maximum with the antiskid actually controlling the deceleration rate.



You're only as good as your last departure.
User currently offlineSpitfire From France, joined Feb 2001, 801 posts, RR: 7
Reply 8, posted (12 years 9 months 4 days 10 hours ago) and read 1188 times:

Actually I 've never used autobrake in MAX (except in simulator) and never had a "live" RTO at V1,only one or two "interrupted" TO before 80 kts...so braking cool...
By the way, as I was initialy trained on a B737-200 without RTO autobraking possibility, I continue on "bigger" airplane to use the same reflex: throttles idles, MAXIMUM "manual" braking (let's say pedals trough the "firewall"!!!), and spoilers (even if already deployed).
I've seen, some years ago, the rubber marks of a DC10 real RTO at V1 in Bujumbura...ended very very close to the end of the runway (15 feet or so...)
Rgds.
Spitfire



Sabena ... Never to be forgotten (12 years already , what a shame !! )
User currently offlineBlackened From , joined Dec 1969, posts, RR:
Reply 9, posted (12 years 9 months 4 days 10 hours ago) and read 1179 times:

What does RTO mean? Something about aborted take-offs I guess.

User currently offlineJan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 50
Reply 10, posted (12 years 9 months 4 days 10 hours ago) and read 1177 times:

RTO=Rejected Take Off
/JM



AeroPresentation - Airline DVD's filmed in High Definition
User currently offlineLMML 14/32 From Malta, joined Jan 2001, 2565 posts, RR: 6
Reply 11, posted (12 years 9 months 4 days 10 hours ago) and read 1171 times:

Does the autobrake work in conjuction with reverse thrust? What I mean is does the system relax the brakes in inverse proportion to the reverse thrust applied?

User currently offlineJan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 50
Reply 12, posted (12 years 9 months 4 days 10 hours ago) and read 1167 times:

I don't think so. The wheel brakes are much more effective than reversing.
/JM



AeroPresentation - Airline DVD's filmed in High Definition
User currently offlineSpitfire From France, joined Feb 2001, 801 posts, RR: 7
Reply 13, posted (12 years 9 months 4 days 9 hours ago) and read 1154 times:

On A340 or A330, when during the TO roll, the trust levers are put in "idle", ground spoilers will deploy (above 72 kts) and max autobrake will occur (everything set "as in the book" !!).

In case of RTO (that's a REAL EMERGENCY): it is always FULL reverse, FULL spoilers, FULL braking. We do NOT "modulate" any of this until a FULL stop (except for the reverse put in idle around 70-60 kts for the risk of durt ingestions and engine surge due hot air ingestion). By the way, reverse "braking" in much more efficient at high speed.
Anyway, there is no link between reverse lever position (and so the "power" of the reverse thrust) and the amount of braking: always MAXIMUM braking till the end of the roll.



Sabena ... Never to be forgotten (12 years already , what a shame !! )
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 14, posted (12 years 9 months 4 days 9 hours ago) and read 1143 times:

What you select (talking B744 here) with the autobrake selector is effectively a deceleration value. The system will try to hold this deceleration by modulating the brake pressure. If you use reverse, the braking power needed to achieve this deceleration will be less, leaving you with cooler brakes.

RTO mode would probably work as above though, maximum braking with anti-skid. If you have an RTO on your hands, a brake fire is probably not your biggest concern...

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineSpitfire From France, joined Feb 2001, 801 posts, RR: 7
Reply 15, posted (12 years 9 months 4 days 8 hours ago) and read 1131 times:

That's right FredT, it's a preselected decelaration rate , always the same with or without reverse. That's the idea for the normal use of the auto brake system.

And that's right also, I prefer to stop 150 yards BEFORE the end of the rwy (even with a brake fire --> emergency evac) than 10 yards AFTER, in the mud and with a broken landing gear (well, the mud could be a good brake cooler, but....  Laugh out loud )
Spitfire



Sabena ... Never to be forgotten (12 years already , what a shame !! )
User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 16, posted (12 years 9 months 4 days 5 hours ago) and read 1096 times:

Normally, the ABS in RTO or MAX will not slow the aircraft at a preselected decel such as LO or MED but rather send full hydraulic pressure to the brakes.

At this point the max decel rate is under the jurisdiction of the antiskid system who, dare I say, modulates the pressure (or more properly said, vents excess pressure).



You're only as good as your last departure.
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