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Changing auto brake setting during roll out

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Changing auto brake setting during roll out

Old 30th Jul 2020, 07:44
  #61 (permalink)  
 
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I checked two different airline's FCOM as well as manufacturer's FCOM and they are silent on changing AB selection during roll out. AB definitely reduces the brake wear as it is a single application also it is even braking. Now the question of setting change, if company forbids then you must not but it remains company specific. System wise there is no problem. The objections that are valid are PF shouldn't do it, also even if PM did it it's a push button and may not engage so he has to ensure that it does and that cannot be monitored by PF who should be looking ahead. Besides selecting a higher rate is opting for more braking whether it will suffice is a guesswork. So taking over manually is a single action solution. However if someone wants to change AB selection during rollout it is not forbidden by every airline.
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Old 30th Jul 2020, 08:06
  #62 (permalink)  
 
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Originally Posted by vilas View Post
I checked two different airline's FCOM as well as manufacturer's FCOM and they are silent on changing AB selection during roll out. AB definitely reduces the brake wear as it is a single application also it is even braking. Now the question of setting change, if company forbids then you must not but it remains company specific. System wise there is no problem. The objections that are valid are PF shouldn't do it, also even if PM did it it's a push button and may not engage so he has to ensure that it does and that cannot be monitored by PF who should be looking ahead. Besides selecting a higher rate is opting for more braking whether it will suffice is a guesswork. So taking over manually is a single action solution. However if someone wants to change AB selection during rollout it is not forbidden by every airline.
My airline doesn't say I can't use my inboard arm to use the sidestick and my outboard arm to control the thrust levers either.
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Old 30th Jul 2020, 08:20
  #63 (permalink)  
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Originally Posted by Check Airman View Post
My airline doesn't say I can't use my inboard arm to use the sidestick and my outboard arm to control the thrust levers either.
But you would if you could?
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Old 30th Jul 2020, 08:32
  #64 (permalink)  
 
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Originally Posted by Check Airman View Post
My airline doesn't say I can't use my inboard arm to use the sidestick and my outboard arm to control the thrust levers either.
Are you sure? Before you strap up in simulator for your first FFS in your type rating something is elaborately explained on how to adjust the outboard arm rest for the outboard arm. May be long time ago you forgot.
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Old 30th Jul 2020, 10:09
  #65 (permalink)  
 
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Originally Posted by Vessbot View Post
I have yet to fly a plane with auto brakes so no first hand experience, but all this talk gives me the feel of watching when someone's flying by twiddling the heading and VS knobs like an Etch-a-sketch and making a harder job for themselves, than simply using the yoke.
Nothing wrong with flying an aircraft by "twiddling" heading and V/S while on autopilot - most airliners are designed to do exactly that to make short term changes to flight path using the FCU ('glare-shield') controls, without having to disconnect the AP.

95% of the time, this is how we fly radar vectors and vertical profile to intercept an ILS, for example. It makes the job easier, not harder - especially when you are in busy airspace such as the London TMA, when it is not helpful if PF is hand-flying.

However, unlike the FCU controls, I don't think the auto-brake selector is designed or intended to be manually modulated (changed) during its operation.



PS, there is an argument that not hand-flying causes our manual skills to become rusty, but that is for another thread.
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Old 30th Jul 2020, 10:11
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I occasionally use this technique when the planned exit point falls between two autobrake settings but only if the PM has been briefed to change it on request. I find it smoother (and better for passenger experience) to land with a higher setting and reduce it rather than the other way round.

When Iím positioning and someone takes out the autobrake then applies jerky heavy braking, from the reactions of those around me they appear to think that the chances of going off the end have dramatically increased. A firm landing followed by a gentle rollout is preferable to a smooth touchdown followed by increasing retardation, it seems...
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Old 30th Jul 2020, 12:02
  #67 (permalink)  
 
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+1

I think that a sudden increase in heavy braking (to make an exit) is more uncomfortable and frightens the passengers more - they think we are about to go off the end - than an initial medium retardation after touchdown that then reduces or ceases.

Unless we have been told to vacate at the end, or at a very distant exit, I like to use medium autobrake (A320 family), and as soon as I can feel and assess the retardation rate, I can either leave medium auto-brake in or drop it out by applying gentle manual braking if it is too much.

Last edited by Uplinker; 30th Jul 2020 at 12:14.
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Old 30th Jul 2020, 17:18
  #68 (permalink)  
 
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Thank you vilas for your clarification on OEM FCOM vs company FCOM.

I do think we are not supposed to be pushing buttons in the middle of a landing roll. Takeover manually if your setting isn’t doing what you wanted
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Old 30th Jul 2020, 18:14
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Originally Posted by Chesty Morgan View Post
But you would if you could?
Assuming Iím still employed when Iím due for my next sim session, maybe Iíll give it a shot
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Old 30th Jul 2020, 18:16
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Originally Posted by vilas View Post
Are you sure? Before you strap up in simulator for your first FFS in your type rating something is elaborately explained on how to adjust the outboard arm rest for the outboard arm. May be long time ago you forgot.
Ha! Good point. Youíre probably right.
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Old 30th Jul 2020, 18:33
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Originally Posted by Escape Path View Post
Thank you vilas for your clarification on OEM FCOM vs company FCOM.

I do think we are not supposed to be pushing buttons in the middle of a landing roll. Takeover manually if your setting isnít doing what you wanted
I was just saying that most airlines suggest that if not satisfied with deceleration then take to manual braking without expressly forbidding setting change in mid roll like your airline does. As I pointed out in AB setting change midstream there are too many variables. I would myself prefer to change to manual braking.

Last edited by vilas; 31st Jul 2020 at 06:20.
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Old 30th Jul 2020, 20:47
  #72 (permalink)  
 
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The Autobrake settings equate to pressures:
ē Autobrake setting 1 - 1250 PSI equates to 4 ft per second squared.
ē Autobrake setting 2 - 1500 PSI equates to 5 ft per second squared.
ē Autobrake setting 3 - 2000 PSI equates to 7.2 ft per second squared.
ē Autobrake setting MAX and RTO - 3000 PSI equates to 14 ft per second (above 80 knots) and 12 ft per second squared (below 80 knots).

If the autobrake is stopping you too quickly, then it's easy to as the PM to select a lower setting, or simply gently apply brakes until the disarm like comes on, at this point you will have the same pressure as the system, conversely if more stopping is required either select a higher setting or apply brakes gently and increase the pressure. The common mistakes are jolts from over ambitious disarming via the switch or stamping on the brakes.
Remember some landing conditions dictate the use of autobrakes so its not a personal choice
Its much safer usually to manually brake to make the required adjustments rather than have heads down in the cockpit,

Last edited by Kirks gusset; 30th Jul 2020 at 21:18.
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Old 30th Jul 2020, 21:12
  #73 (permalink)  
 
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There is of course a thread on PPRuNe Technical about brake application and wear:

The logic or illogic use of hard braking with carbon brakes on long dry runways
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Old 30th Jul 2020, 21:18
  #74 (permalink)  
 
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Carbon brake wear is primarily dependent on the total number of brake applications — one firm brake application causes less wear than several light applications. Safety and passenger comfort should remain the primary considerations.

Boeing article quote
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Old 6th Aug 2020, 21:35
  #75 (permalink)  
 
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Originally Posted by Uplinker View Post
Nothing wrong with flying an aircraft by "twiddling" heading and V/S while on autopilot - most airliners are designed to do exactly that to make short term changes to flight path using the FCU ('glare-shield') controls, without having to disconnect the AP.

95% of the time, this is how we fly radar vectors and vertical profile to intercept an ILS, for example. It makes the job easier, not harder - especially when you are in busy airspace such as the London TMA, when it is not helpful if PF is hand-flying.
Weíre talking about different things. Youíre talking about normal usage of heading mode, which is setting headings for discrete lengths of time during which you intend to fly that heading (most often because of a vector). What Iím talking about comes up pretty rarely so maybe you havenít seen it, in which case you should count yourself lucky.

But when you do, itís eye-watering. Like thereís the LGA 31 expressway visual, an approach in the US where for a large segment of it youíre supposed to follow a road. Every once in a while Iíll fly with someone who isnít comfortable flying and wants to ďreduce the workloadĒ and use the autopilot, and theyíll be virtually unable to take their hands off the heading knob having to make constant corrections for the initial overshoot, later overshoots from that overshoot (as inevitably the slow roll rate and overall response of the AP does not match up with the ground track he thought was gonna happen) wind changes, slight turns in the road, etc., all the meanwhile heís trying to manage the VS as well.

Thereís another control for that! And this is not what the autopilot was meant for.
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Old 7th Aug 2020, 04:38
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Originally Posted by Vessbot View Post
We’re talking about different things. You’re talking about normal usage of heading mode, which is setting headings for discrete lengths of time during which you intend to fly that heading (most often because of a vector). What I’m talking about comes up pretty rarely so maybe you haven’t seen it, in which case you should count yourself lucky.

But when you do, it’s eye-watering. Like there’s the LGA 31 expressway visual, an approach in the US where for a large segment of it you’re supposed to follow a road. Every once in a while I’ll fly with someone who isn’t comfortable flying and wants to “reduce the workload” and use the autopilot, and they’ll be virtually unable to take their hands off the heading knob having to make constant corrections for the initial overshoot, later overshoots from that overshoot (as inevitably the slow roll rate and overall response of the AP does not match up with the ground track he thought was gonna happen) wind changes, slight turns in the road, etc., all the meanwhile he’s trying to manage the VS as well.

There’s another control for that! And this is not what the autopilot was meant for.
Flying the expressway visual in heading mode should be illegal. I've also flown with somebody who's insisted on doing the river visual with the AP (albeit in NAV mode). What's the point?
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Old 7th Aug 2020, 09:38
  #77 (permalink)  
 
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Not that I want to weigh in, but I loathe the practice of changing autobrake settings on the landing roll. If PF does it, I think it's an example of extremely poor judgement and if they ask PM to do it they're forcing the non-handling pilot to look inside and move something unmonitored at a critical moment. On top of that it's not good for passenger comfort because there's a jerk from the brakes whether they're increasing or decreasing the force. 787 even has a deceleration indicator in the HUD to help you judge the braking.

If you're not capable of smoothly disconnecting the autobrake and modulating the brakes to an appropriate level manually then IMHO you shouldn't be flying a passenger aircraft. Or driving a car, frankly...
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Old 7th Aug 2020, 12:13
  #78 (permalink)  
 
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@ Vessbot and Check Airman, Ah OK.

However, if someone is not able to lay off drift to track something, and/or is overshooting a track, then how would making them hand-fly as well help the situation? Wouldn't that add even more inaccuracies?

Last edited by Uplinker; 7th Aug 2020 at 16:26.
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Old 7th Aug 2020, 16:13
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I think youíre talking about the parkway visual (aka Canarsie visual) to jfk. Iíve never seen anyone use the AP for that approach. Did you find it easier? What vertical mode did you use?

I think what Vessbot is talking about re HDG mode is the fact that the AP reacts way too slowly for the fine correction thatís needed to fly those approaches, so it actually increases workload.
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Old 7th Aug 2020, 16:25
  #80 (permalink)  
 
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Actually sorry, no I was briefed on it very comprehensively but never actually flew it - my bad

I'll get my coat.........
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