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  • Autobrake question

    How is the Auto brake selected?

    I know the selections are RTO (Rejected Take-off), Off, 1, 2, 3, MAX. What factors would lead a C/O or F/O to select a landing level of 1 over MAX?

    For the people that may not know what I'm talking about.
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  • #2
    They are selected based on the level of deceleration you require.

    Lowest level is 1, highest is Max/RTO.

    Which one you select depends on aircraft type, weight, runway length and condition (ie dry, wet, contaminated), desired exit, and servicibility of other stopping devices.

    Take the 767 for example. There are tables that show the approximate stopping distance using each setting. On a dry runway where you want to exit say 2000m in, then you'll use say AB 2 or 3. If you wish to roll through to the end of a 4000m, you'll use 1.

    Max is rarely used, only on very limiting runways, or in poor weather conditions. It stops you in a real hurry! Maximum manual braking stops you slightly faster than maximum autobrake.

    RTO is selected prior to takeoff, and is armed. It activates when certain actions are taken, and it applies maximum braking.

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    • #3
      The canadian space shuttle does not have autobrake so I dunno

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      • #4
        Generally the lowest auto brake selection is used for the conditions expected. You can manually increase the brake pressure using the pedals.

        MAX braking burns up tires and brakes. The setting tends to overheat the brakes.

        A 747-200F using MIN. brakes gets between 250 and 300 landings from a set of brakes and about 100 landings from a set of tires. Using MAX braking cuts the number of landings available from the brakes and tires in half. MAX could cut tire life to a single landing if the brakes get hot enough to melt the fuse plugs.
        Don
        Standard practice for managers around the world:
        Ready - Fire - Aim! DAMN! Missed again!

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        • #5
          It would depend upon how long the runway is ,where you want to stop and the condition of it.

          For instance if I was landing a 767 on runway 23 at CYYZ in a snow storm I would more likely use Max Auto then 1 even though 23 is the largest at CYYZ because of the conditions and if I was landing the same 767 on 24R in sunny and clear conditions I would use 1 or 2 depending on where I want to exit the runway.

          Nehal

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          • #6
            Originally posted by C-FMWQ View Post

            For instance if I was landing a 767 on runway 23 at CYYZ in a snow storm I would more likely use Max Auto.
            I would use max reverse and gradual minimal manual braking, but that's just me.

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            • #7
              Originally posted by Spad13 View Post
              I would use max reverse and gradual minimal manual braking, but that's just me.
              Yeah it would really be up to you because in snowy weather most pilots would rather get the plane on the ground safely then worry about it being the softest roll out, but that's just how I see it.

              Nehal

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              • #8
                Originally posted by C-FMWQ View Post
                Yeah it would really be up to you because in snowy weather most pilots would rather get the plane on the ground safely then worry about it being the softest roll out, but that's just how I see it.

                Nehal
                I think we're talking about two different things. What I'm talking about has nothing to do with how soft (or hard) the touchdown is, I'm referring to what happens after the touchdown. Then again, I'm probably not qualified to talk about this, seeing as I've actually landed on 23 at YYZ. As well as on 24L and R. Oh well.

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                • #9
                  It would depend if you were landing in dry powdery non-melting snow vs a runway with the posibility of directional control wouldn't it

                  That said, I'm not sure I'd want to land on any runway where I needed to use max auto without a pretty good reason.

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                  • #10
                    Originally posted by Spad13 View Post
                    I think we're talking about two different things. What I'm talking about has nothing to do with how soft (or hard) the touchdown is, I'm referring to what happens after the touchdown. Then again, I'm probably not qualified to talk about this, seeing as I've actually landed on 23 at YYZ. As well as on 24L and R. Oh well.
                    I hate that airport....such a pain to taxi around. Its really not that busy that they need 3 ground control frequencies.

                    My favorite was when they were having all departures go off of 23 even though everyone had to be de-iced. Nothing like taxiing to one side of the airport, get deiced, then taxi past where you just were to go to the OTHER side of the airport to take off.

                    Then there's YUL who once told me mid flare "Acey XXXX plan to exit the runway at (whatever that taxiway is)". Yeah...kinda busy

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                    • #11
                      Don't confuse "AUTO-BRAKES" with "ANTI-SKID". They are two different systems. Anti-skid works with or without auto-brakes.

                      The auto-brake system applies the brakes according to the rate of deceleration the pilot wants. All deceleration rates are based on a dry runway.

                      The anti-skid system prevents wheel skid from more brake pressure being applied than the friction between the wheels and runway can support.

                      When landing on a wet, slick runway, the anti-skid determines the max braking that can be applied. Auto-brake applies the pressure, anti-skid modifies the pressure if that pressure exceeds the friction available.
                      Don
                      Standard practice for managers around the world:
                      Ready - Fire - Aim! DAMN! Missed again!

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                      • #12
                        This is what I understand, but I very well could be wrong so please (Don) correct me if so:

                        The autobrake will aim for a given longitudinal deceleration (except in MAX and RTO where it will aim for as much braking as possible). So the "amount of brakes" it will apply will be a function of other factors. For example, if you are using max reverse, the amount of braking needed to reach the desired deceleration will be less than if using no reverse.

                        On a very slippery runway, there might be no difference in what autobrake setting you choose, since the antiskid might activate at the lowest settings: If the traction between the tires and the runway is not enough to reach a "Autobrakes 1" level of deceleration, then the deceleration will be the same (less than 1) in any setting. The Autobrake doesn't have the capability to improve the available traction with the runway.

                        Finally, I'm don't know why, but in all the (few) landings in MD-80s I've witnessed (two in person and a few more in videos) the PNF asked "Do you want any autobrakes", and the PF answered "No". (All the cases were in Austral Líneas Aéreas, most of them but not all landing in Buenos Aires City Airport, a some 6300ft long runway, one of them in raining).

                        So when answering "what factors make you chose one selection or another", please include the "Off" as one of the possible choices.

                        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                        --- Defend what you say with arguments, not by imposing your credentials ---

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