B737 3-5 /ng stuff

[spierpoint jones]

Condition: With say autobrake 1 selected can you ,(during landing deceleration ) select a new autobrake rate of braking ,say go to 2 or even, why not.... max.....nothing about this exists in the ops manual.

My engineers are at an impass. I think you can perform this selection on the B744 ,but this thought is based on pure conjecture....
Thanks to all

[The Greaser]

Indeed you can, above a certain speed, 60 or 80 knots if i remember correctly.

[john_tullamarine]

.. why would you ?

(a) distraction/diversion of attention

(b) manual braking

[Ziggy]

From FCOM VOL II B737-800:

"Landing autobrake setting may be selected after touchdown prior to decellerating through 60kts of groundspeed."

And further down:

"To maintain the selected landing deceleration rate, autobrake pressure is reduced as other controls, such as thrust reversers and spoilers, contribute to total deceleration. [B] The deceleration level can be changed (without disarming the system) by rotating the selector. [B] The autobrake system brings the airplane to a complete stop unless the braking is terminated by the pilot."

In this contex, does it suggest that you can change it after touchdown? I think it does.

Don't know about the Classics.

Greetings, Ziggy

[Flight Detent]

Yes, those selections can be made in both the B737NG and the Classic B747.

Cheers,
FD

[spierpoint jones]

thanks to all for responding......

why not ? well why not if you have the option...use all available means at your disposal....

My love to OZ and merry bondi christmas to everyone

[LEM]

I've seen the Captain asking for a new setting just before vacating at VHHH in a Cathay 744 video.

On the 744 the selector is on the stand and very reacheable by PNF.

Not so on the 737, where you have to lean forward. Sounds totally nonsense on the 737 (use your feet and that's it!).

[The Greaser]

I must say I have used it to turn off the autobrake during the rollout as I find that it is much smoother than either manually braking to disconnect or lowering the speedbrakes.

[HSWL]

My contact at Boeing Seattle tells me that they do not recommend changing of autobrake settings in the middle of the landing run - even though the technical capability is available. Moreover, he said that there is no need to switch off the autobrake selector after landing during the after landing checks, as it is covered in the shut down checks.

[Shaka Zulu]

HSWL you are missing the point that The Greaser was making about setting the autobrake select switch to off.
What The Greaser means is that, if you do not disconnect the autobrake by stamping on the brakes or putting the speedbrake lever down, the autobrake will continue braking till the aircraft is actually slowed down to 0kts. Not very desirable since you want to turn off the runway!

If you do not have your feet on the brakes with the same pressure as the autobrake is braking and you put the speedbrake down the aircraft will suddenly lurge forward again (apparent feel) due to less braking. Not v nice sometimes.

Or by disarming the autobrake by manual braking you sometimes have to brake real hard to simply disconnect it, which sometimes even means antiskid activation. Not v nice either!

By switching the selector to off it can be done in a very smooth fashion

[Alaskan Timber]

Although nothing is really wrong. The best way to switch from autobraking to manual braking is by pushing the pedals. If you do it smoothly nothing will be noticed by the pax.

HSWL is right, it is not recommended to switch autobraking from, say 2 to 3.

[meatball]

Nicer even is to mount and use if necessary reverse thrust with autobrake on, of course, keep feet on brakes no pressure until 80 kts at which then you cancel reverse N1 and start adding foot pressure whilst releasing speed brake lever slowly to retracted position. At 60 cancel reverse totally. The transistion from autobrakes to manual is smooth and pax won´t even notice:ok:

[Dehavillanddriver]

Alaskan Timber and Meatball do you fly the classic or NG 737?

If you only fly the classic, you are 100% correct.

The autobrake on the NG takes a considerable amount of force to disconnect via the pedals.

So much so that in some aeroplanes you can almost stop the aircraft using the pedals and the autobrake won't come out.

Short sharp jabs on the pedals get the autobrake out, but feel terrible in the cabin, dropping the spoilers or selecting the switch to off are the smoothest options IMHO.

[Alaskan Timber]

Hey Dehavillanddriver,

Most of my flying hours are on the classic. Since a couple of months I also fly the NG. The situation you describe I didn't experience (yet), but I indeed noticed that on all the NG's you really have to push the pedals firmly to brake at all and that there is big difference per aircraft.

Thanks for the info.

[jonny dangerous]

Hey all, I flew with a Captain not long ago (we're NG drivers) and we were discussing this exact issue. He was good enough to volunteer that about a year ago he reached up during landing roll to deselect the autobrakes, and accidentally rotated the selector past the "off" setting and selected "RTO". Now, I believe the Boeing FCTM or Vol 2 says that RTO won't activate under such conditions,but PRESTO!, and the airplane was stopping way too fast!!!

In sum, can you do it, yes I suppose if SOP's allow, but as this particular Captain experienced, it might not be prudent. In addition, the potential for distraction etc by bending down and forward doesn't seem to warrant the effort.


Cheers

[Mr.Buzzy]

Have found that the slightest amount of differential brake will quickly bring on the disarm light.

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[batty]

A Boeing directive was issued to advise operators not to select Autobrakes to Off Manualy in the landing roll since there have been several instances of people selecting through the 'Off' position into the 'RTO' position. Boeing say that the logic is such that it can cause RTO braking at any speed after autobraking has initiated.
They recommend either manual braking or selecting the speed brake to down to cancel autobrakes

[BLE]

The different feel from NG to classic is due to the different types of feedback springs fitted to the brake pedals. A lot stiffer springs on NG.

To disconnect autobrakes by using pedals, it will take manual input equalling approx. 800 psi, regardless of NG or classic.

The sensation of acceleration after the manual input only indicates the autobrake system is applying a pressure GREATER than 800psi.
If you feel the brakes grabbing, which most people end up doing, the autobrake system is providing the set deceleration rate in conjunction with thrust revers that requires LESS than 800psi onto the brakes.

Rotating the selector from any setting to OFF is fine, but you do run the risk of applying 3000psi immediately into the system if you by accident select RTO above approx. 60 kts GS.
The aircraft will then have a nice imprint of your face with a very surprised expression on the inboard ND:p

Disarm the system by slowly stowing speedbrakes.
If you do not NEED to brake above 100kts, leave the autobrake to OFF!
Settings 3 or MAX is to be used when conditions demand, meaning limited wet or contaminated runways, strong crosswinds or low vis.

Anything else is waste of money and good brake disks.
We are talking steel, not carbon here.