B737 NG RTO Braking

[fireflybob]

Not got access to the manuals here but always understood that the RTO autobrake gave max braking and therefore minimum stop distance but recently a respected trainer advised me that max manual braking would stop you circa 150 metres shorter.

Is that so?

[fireflybob]

B737 NG RTO Autobrake

Not got access to the manuals here but always understood that the RTO autobrake gave max braking and therefore minimum stop distance but recently a respected trainer advised me that max manual braking would stop you circa 150 metres shorter.

Is that so?

[Pickled Props]

The reputation of your trainer would seem to be upheld!

Quote from the "Wheel brakes" section in the Boeing flight crew training manual.

"MAX is used when minimum stopping distance is required. Deceleration rate is less than that produced by full manual braking."
Can't verify the 150m bit but it would seem reasonable, the standard of pilot tech manuals is a bit shallower these days.

Landing autobrake positions (1,2,3 and MAX) command a rate of deceleration which are affected by other retardation devices, spoilers or reversers etc. But max manual is the physical maximum stopping capebility of the brakes and anti-skid working together provided your boots are big enough!
Think this logic applies to all of Mr Boeings products.

I understand, although can't find a reference to hand, that RTO is the same as max manual and pays no attention to the rate of deceleration.

[Sciolistes]

Pickled Props,

Terminology confusion. MAX is an autobrake setting which commands a deceleration rate. The question was RTO compared to max manual braking which both demand maximum braking capability. I would be surprised if max manual beats RTO by nearly five hundred feet though. Perhaps something to do with how quickly RTO kicks in vs stamping on the pedals at first sign of trouble?

[RAT 5]

True, but with a caveat. One might be tempted to disconnect RTO when in that scenario. Accel/stop calculations have been made using RTO; plus I would hazard the guess that while 2 great size 13's stomping on the brakes, such that your backside is off the seat, will cause your nose to be pressed hard against window, when you start trying to steer with same said piston pumpers you will then relax the pressure on one or both of the pedals and revert back to stopping performance less than max and possibly less than the RTO you've just disconnected.
Further, why is foot pumping pedal pushing called 'manual' braking? Which part of the hand is involved?

[Denti]

I doubt you can beat max brake pressure, which is what RTO does.

[Quality Time]

I'm with Denti.

RTO provides the most effective braking.

Often gets mixed up with 'Max Autobrake'

[b737b800]

He is correct.
The Shortest braking distance is achieved with max manual braking. QRH contains different forms where you can see the difference in braking distance for different aircraft conditions and auto brake settings

[mrjet]

You are right bob. Rto gives max system pressure (assuming you're not antiskid limited). Theoretically max manual and Rto are the same, however in practise it is very hard to achieve the same stopping distance with manual braking due to the fact that a pilot will inadvertently reduce brake pressure whilst turning and a secondary effect of that is that the antiskid system will continuously work to find the correct level of braking thereby increasing stopping distance.

I think you're trainer may be mixing up Rto and auto brake max.

[Callsign Kilo]

This is true, max manual braking + max reverse thrust provides the greatest stopping capabilities of the aircraft. If you consider the PI advisory section of the QRH for non normal operations, all figures are based on the application of max reverse thrust and max manual braking. No reference is made to autobrake settings.

PS - max manual relates to maximum application of brake pressure - no modulation. It therefore suggests that the anti skid should work in tandem with max applied braking pressure

[captplaystation]

Shouldn't this be in "Tech Log" ?

Anyway, don't have a manual to hand either, but my recollection was that max manual braking was shorter than autobrake in MAX, as MAX was still a deceleration rate, rather than truly maximum braking.
However, I always believed that RTO was the equivalent of maximum manual braking, have I been believing the wrong thing for 22years ? Duh ! or has it been wrongly described in manuals at some stage in the past.?

[nick14]

Im sure in reference to landing distance max auto brake gives a greater stopping distance than max manual braking.

However I have been under the impression that the system pressure was 3000 at maximum and therefore max manual or RTO will give you the shortest stopping distance in the event of an RTO. Although I would say humans being humans will no doubt produce a greater stopping distance due to thinking distance and errors in application of the brakes.

Please educate us all anyone!

[Denti]

RTO gives max brake pressure (modulated by anti-skid if need be), you can't get better stopping performance. Apparently quite a lot confuse it with the auto brake setting MAX which commands a deceleration rate but is a completely different kind of thing than RTO. Poor initial training rearing its head...

[captplaystation]

In reality the autobrakes will, via RTO, get on the brakes sooner/harder & continue to apply them to the max, regardless of rudder input by your size 10's , much more consistently than you will. Every company I have flown with on the 737 (a few) have always advocated avoiding manual braking & letting RTO do the job ,whilst briefing PM to call if "autobrake disarm" illuminates. I have always assumed this was not only due to more consistent results (as discussed above) but the fact that the system was, in any case, giving you the absolute max courtesy of RTO. I am sure somewhere in the old grey matter I remember it being phrased something along the lines of "RTO is the equivalent of max manually applied pilot braking with no modulation to achieve a desired rate"


Edited to say, perhaps this ( & the similar thread appearing in Tech Log ) should be combined with the "737 common misunderstanding" one, as it seems a few of you misunderstood Mr Boeings RTO function ?

[misd-agin]

RTO is everything the plane can do.

Max manual is everything the plane can do.

Max Autobrakes, a landing a/b setting, is less then max manual OR RTO.

Data I have for a 140,000 lb a/c shows a landing roll reduction of 204 meters when using max manual braking vs. max autobrakes.

Even if it's a respected Captain, TRI, TRE, ask them to show you the data. The data I checked for 120,000 lbs, 130,000 lbs, and 140,000 lbs showed 204-207 meters.

[Sciolistes]

RAT 5,

Accel/stop calculations have been made using RTO

Actually the wording in the AFM is that the performance takes RTO and max manual braking into account.

However, your point that RTO would be more reliable is understood too.

[B737-pilot]

FCOM chapter 14: '' if the take off is rejected after reaching a wheel speed of 90 Kts,maximum braking is applied automatically when the thrust levers are retarded to IDLE. Braking force is the equivalent of full manual braking. ''

Pro arguments for using RTO braking ( in my opinion):
a) faster brake application
b) constant/ maximum brake pressure / aplication till a complete stop.

[Sciolistes]

whilst briefing PM to call if "autobrake disarm" illuminates

OK, perhaps I'm being a bit too picky, but why brief this, it is a recall item? The irritating sod that I am, if a Capt wants to brief some recall items, I quiz him in on the stuff he forgot to mention, otherwise it appears that either he is misdirecting me or he doesn't know.

Also, why is this in ToE? It is in Tech Log too.

[stilton]

You won't improve on RTO autobrakes.



This is maximum braking, not a maximum rate, it is all the braking performance available.


There is a temptation to jump on the brakes manually in the event of a rejected take off but you are better off letting this braking function do it's thing while you keep it straight.

[de facto]

Sciolistes,
Whats wrong with briefing a possible a/b diesengagement?maybe it is company sops?
What happens when you land and the a/b disengage unintentionally?would you rather the other pilot remain quiet?it does happen you know...

You quote:' if a Capt wants to brief some recall items, I quiz him in on the stuff he forgot to mention, otherwise it appears that either he is misdirecting me or he doesn't know.' you may have issues my friend