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-700 stopping distances seem short to anyone else?

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    -700 stopping distances seem short to anyone else?

    This is purely anecdotal, but the stopping distances for the -700 feel shorter than what I'd expect. I don't see a need to ever use any autobrake setting beyond 1. I'm curious to know what the SMEs here think about it.
    Alex Pugh

    #2
    Do something. Set typical weather conditions, nothing too crazy. Set a normal landing weight and measure the actual landing distance. For example, use the top down view and note where the airplane stops in reference to one of the taxiways and then use google earth to measure the distance you required to stop.

    Write all parameters here and we'll compare them to the real Boeing OPT. I'm attaching a screenshot of the OPT showing all the information needed to calculate LDR. It has to be on dry rwy and don't use more than idle reverse. And it has to be a typical European airport.
    Attached Files
    Last edited by Aeromar; 08Feb2020, 18:50.
    Omar Josef
    Spain

    Comment


      #3
      Alex,

      Autobrake got a pretty significant update to improved it's ability to target the correct deceleration rates for braking. (It was over aggressive, previously)

      I ran a quick test with a 700 just now and it does seem something is amiss. In a 700 landing at 115,000lb w/ABRK 2 you should see a landing distance (measured from 50' AGL and normal flare) of around 5,600'. My test just now came in about 1400' shorter than that.

      I pulled a data dump of the autobrake module and it showed that at ABRK 2 the airplane reached a nominal acceleration rate of 8.52 ft/sec/sec, which is extremely high. (ABRK 3 is 7.0, for example)

      ABRK 2 should give you an acceleration of only 5.0 ft/sec/sec.

      This system got about 200 instrumented landings on it during the last update cycle in order to ensure the new acceleration controller was working and that the results matched the performance computation results. That data collection was within a few percent and we signed it off, so i'm mystified as to what is happening here.

      I'll dig into it and let you know what I find.

      Robert S. Randazzo
      PMDG Simulations
      http://www.pmdg.com


      Comment


        #4
        Originally posted by rsrandazzo View Post
        Alex,

        Autobrake got a pretty significant update to improved it's ability to target the correct deceleration rates for braking. (It was over aggressive, previously)

        I ran a quick test with a 700 just now and it does seem something is amiss. In a 700 landing at 115,000lb w/ABRK 2 you should see a landing distance (measured from 50' AGL and normal flare) of around 5,600'. My test just now came in about 1400' shorter than that.

        I pulled a data dump of the autobrake module and it showed that at ABRK 2 the airplane reached a nominal acceleration rate of 8.52 ft/sec/sec, which is extremely high. (ABRK 3 is 7.0, for example)

        ABRK 2 should give you an acceleration of only 5.0 ft/sec/sec.

        This system got about 200 instrumented landings on it during the last update cycle in order to ensure the new acceleration controller was working and that the results matched the performance computation results. That data collection was within a few percent and we signed it off, so i'm mystified as to what is happening here.

        I'll dig into it and let you know what I find.
        I agree something seems to be off in the -800 as well, and MeatServo's tests seem to confirm that. Good to hear it's being looked into.
        Santiago Vegega

        Comment


          #5
          Just landed in the 800 Autobrake 3, can second all of the above..... If that was a real flight it probably would have snapped my neck off 😁 Somethings definately up....If it was over aggressive before now it wants to punch you in the face....its wayyyy more effective than it was before. The rest of the flight was sublime however! Loving the new landing characteristics. No more floatys!
          Last edited by nopixar; 08Feb2020, 20:48.


          Miles Codrington

          Comment


            #6
            That's curious. I do NOT have the -700 (yet) and did a flight with the -800 today. I used autobrake 2 into PAKT and it "felt" fine actually. However I was nearly empty as I simulated a ferry flight so my vref was very low too.
            i7-6700k, GTX 1080TI, 32GB DDR4 RAM @2666MHz, 4k

            Marc Ehnle

            Comment


              #7
              Any progress on the culprit of this behavior? I find a temporary fix is to use Autobrake 1 for most landings, as it gives similar stopping distances to Autobrake 3 at present, or use manual braking for anything less. Thats for both the 800 and 700. They behave the same.
              Last edited by nopixar; 15Feb2020, 13:20.


              Miles Codrington

              Comment


                #8
                Just landed at CYYZ this morning in the -700 with a vref of 125kts... auto brake 2 and I was stopped on RWY 23 hardly past the last TDZ markers. Definitely not normal braking. I really like the updated physics around landing, it seems much more sensitive and dynamic. I can still nail -60 to -150 fpm landings no problem and the nose doesn’t slam down as fast anymore
                - DREW ROMANOVYCH -

                Comment


                  #9
                  Yeah I have noticed that it seems way to I guess powerful. Tried it at MDW landing ILS 31C calm winds and also visual landing. Charts says flaps 40 speed brake 3 or ma . So I set it up full ZFW flaps 40 speed brake 3. Landed exactly on the spot and was pretty much stopped before hitting 22L/04R. So I went back same settings flaps 40 but this time auto brakes 2 and it felt the same and then with auto brake 1 it felt like how it should be with be with auto brake 2. It's short on my end for the weight tested
                  Alex Kulak
                  PMDG Studier and flyer

                  Comment


                    #10
                    Originally posted by nopixar View Post
                    Any progress on the culprit of this behavior? I find a temporary fix is to use Autobrake 1 for most landings, as it gives similar stopping distances to Autobrake 3 at present, or use manual braking for anything less. Thats for both the 800 and 700. They behave the same.
                    Sure would be a great candidate for one of those "microupdates" we always hear about but never seem to happen.
                    Alex Pugh

                    Comment


                      #11
                      Originally posted by AirBadger View Post

                      Sure would be a great candidate for one of those "microupdates" we always hear about but never seem to happen.
                      Patience my young padawan
                      Alex Kulak
                      PMDG Studier and flyer

                      Comment


                        #12
                        Some News About it ? I feel the same Thing with the 800 since the last update rsrandazzo



                        Christian Urban

                        Comment


                          #13
                          Originally posted by Christian Urban View Post
                          Some News About it ? I feel the same Thing with the 800 since the last update rsrandazzo


                          Rest assured, PMDG will break something else with the next patch, just like in all the other patches released. My advice is just to learn to live with it and never, ever update. Just don't.

                          Signed,

                          Aaron Cumberland

                          Comment


                            #14
                            I can't help but wonder if it is something with the mass of the aircraft being taken into account - here is an experiment to try even though unrealistic in real-life. Set thrust reversers to max from a cold stop with no parking brake. As you gain a little speed rolling backwards, use your controls (or keyboard) to set the engines to normal forward idle, non-reverser. The plane instantly, without pause, starts rolling forward. I'm no 737 pilot but I can't see this abrupt transition happening in real life. There is no transition at all. Snap.

                            There was another situation that escapes me at the moment but the plane felt like it had no significant mass. The NGXu doesn't feel heavy anymore like the NGX did.

                            The 2nd derivative equations in calculus (rate of change) seem to have been left out of some of the aircraft algorithms (those that govern motion), which seems to have gone missing in the new code.

                            Not worried - it will get sorted out.

                            Thanks,

                            Mark Trainer
                            Mark Trainer

                            Comment


                              #15
                              Originally posted by rsrandazzo View Post
                              Alex,

                              Autobrake got a pretty significant update to improved it's ability to target the correct deceleration rates for braking. (It was over aggressive, previously)

                              I ran a quick test with a 700 just now and it does seem something is amiss. In a 700 landing at 115,000lb w/ABRK 2 you should see a landing distance (measured from 50' AGL and normal flare) of around 5,600'. My test just now came in about 1400' shorter than that.

                              I pulled a data dump of the autobrake module and it showed that at ABRK 2 the airplane reached a nominal acceleration rate of 8.52 ft/sec/sec, which is extremely high. (ABRK 3 is 7.0, for example)

                              ABRK 2 should give you an acceleration of only 5.0 ft/sec/sec.

                              This system got about 200 instrumented landings on it during the last update cycle in order to ensure the new acceleration controller was working and that the results matched the performance computation results. That data collection was within a few percent and we signed it off, so i'm mystified as to what is happening here.

                              I'll dig into it and let you know what I find.
                              Captain Randazzo,

                              also I experienced extremely short landing distances.

                              Yesterday I flew EHAM to EGPO = Stornoway, Scotland looking for windshear at my destination...
                              Aircraft: PH-XRX, Transavia 737-700. Stornoway provides two runways

                              18/36, 2200 meters, 7218 ft,
                              07/25, 1000 meters, 3281 ft.

                              like this:

                              |
                              |/
                              /|
                              |

                              Due to the predicted winds ...

                              EGPO/SYY STORNOWAY
                              SA 221520 AUTO 25034G56KT 9999 FEW021/// SCT032/// 04/02 Q0992 RERA
                              FT 221355 2215/2224 25022KT 9999 FEW014 SCT020 TEMPO 2215/2224 26025G37KT 6000 SHRA SHRAGS BKN012CB
                              PROB30 TEMPO 2215/2224 27030G47KT 3000 +SHRA BKN007


                              ... I decided to give runway 25 a try,
                              and this despite the fact that with 55.6 tons LW (I had the fuel on board to return to EHAM),
                              and EFB had predicted with max manual braking, full flaps about 3450 ft landing distance.

                              So, I was approaching fully go-around minded,
                              but to my surprise the bird came to a full stop even before crossing runway 18/36 (reverse thrust applied).

                              Looking forward to learning about your findings.
                              Andre(as) Berg --- i7 8700K 12MB 3.7G. MSI Z370 Tomahawk. DDR4 16G. SSD 500G M.2. MSI RTX2080 DUKE 8G

                              Comment


                              • MeatServo
                                MeatServo commented
                                Editing a comment
                                I had the NGXu -600 stopped on a 2100’ runway one night while fooling around after a few pints. Also found weird control issues when you loop and roll her.

                              • Aaron Cumberland
                                Aaron Cumberland commented
                                Editing a comment
                                MeatServo Let's get Boeing and PMDG to collaborate together on an 737Maxx fix, hehehe. Run for cover when they flight test though!

                              • Swaluver88
                                Swaluver88 commented
                                Editing a comment
                                Aaron Cumberland what did I just read 🤣🤣

                              #16
                              Originally posted by rsrandazzo View Post
                              Alex,

                              Autobrake got a pretty significant update to improved it's ability to target the correct deceleration rates for braking. (It was over aggressive, previously)

                              I ran a quick test with a 700 just now and it does seem something is amiss. In a 700 landing at 115,000lb w/ABRK 2 you should see a landing distance (measured from 50' AGL and normal flare) of around 5,600'. My test just now came in about 1400' shorter than that.

                              I pulled a data dump of the autobrake module and it showed that at ABRK 2 the airplane reached a nominal acceleration rate of 8.52 ft/sec/sec, which is extremely high. (ABRK 3 is 7.0, for example)

                              ABRK 2 should give you an acceleration of only 5.0 ft/sec/sec.

                              This system got about 200 instrumented landings on it during the last update cycle in order to ensure the new acceleration controller was working and that the results matched the performance computation results. That data collection was within a few percent and we signed it off, so i'm mystified as to what is happening here.

                              I'll dig into it and let you know what I find.
                              Any news on the deceleration issue, Captain?
                              Thx in advance.
                              Andre(as) Berg --- i7 8700K 12MB 3.7G. MSI Z370 Tomahawk. DDR4 16G. SSD 500G M.2. MSI RTX2080 DUKE 8G

                              Comment


                                #17
                                Any hope for a patch today?
                                Alex Pugh

                                Comment


                                  #18
                                  I must say this is really annoying because you can only use autobreak one or brake manually. Everything else is totally unacceptable. With all due respect, this really needs to be adressed asap as the autobreak system represents a fundamental system. I also wonder how this could go unnoticed during testing.

                                  Mark Tegge

                                  Comment


                                    #19
                                    So, is this going to get fixed any time soon? Seems like a pretty immersion breaking item now. How did this even get past beta testing?
                                    Bogdan Misko

                                    Comment


                                      #20
                                      Originally posted by Airhunter View Post
                                      So, is this going to get fixed any time soon? Seems like a pretty immersion breaking item now. How did this even get past beta testing?
                                      I don't think it'll get fixed anytime soon. Patches for the 777 and 747 are at the head of the queue now.
                                      Alex Pugh

                                      Comment


                                        #21
                                        Originally posted by AirBadger View Post

                                        I don't think it'll get fixed anytime soon. Patches for the 777 and 747 are at the head of the queue now.
                                        Yeah but they can simply push a small update for this very issues via the OC. Nothing major.
                                        Bogdan Misko

                                        Comment


                                          #22
                                          I’m never expectant when it comes to these kind of things. Incredibly patient...However it does seem odd there hasn’t been an urgency to fix this... or at least an update how the investigation is going..At the moment you just have a landing calc Page on the efb that looks pretty, and an aircraft with aircraft carrier capability. Hope its sorted soon has put me off flying it for a while.


                                          Miles Codrington

                                          Comment


                                            #23
                                            Haven't got the NGXu, but as a matter of interest, has anybody had a look at the brakes temps. Are they excessively high, or normal ?
                                            Neil Ward

                                            Comment


                                              #24
                                              Originally posted by Cat3508 View Post
                                              Haven't got the NGXu, but as a matter of interest, has anybody had a look at the brakes temps. Are they excessively high, or normal ?
                                              I usually dont fly airframes with brake temp indicators so I don't know.
                                              Bogdan Misko

                                              Comment


                                                #25
                                                Originally posted by Airhunter View Post
                                                Yeah but they can simply push a small update for this very issues via the OC. Nothing major.
                                                I guess the first question would be if they even figured out what caused it in the first place.
                                                Captain Kevin

                                                Kevin Yang

                                                Comment


                                                  #26
                                                  Originally posted by Airhunter View Post

                                                  I usually dont fly airframes with brake temp indicators so I don't know.
                                                  You could simply switch on the presentation of the indicators to help here....
                                                  Andre(as) Berg --- i7 8700K 12MB 3.7G. MSI Z370 Tomahawk. DDR4 16G. SSD 500G M.2. MSI RTX2080 DUKE 8G

                                                  Comment


                                                    #27
                                                    Originally posted by 19ab67 View Post

                                                    You could simply switch on the presentation of the indicators to help here....
                                                    I've seen the brake temp indicators working after every flight. However, I've never noticed them rise above normal values even with aggressive braking but then I always use autobrake above 40 kts and have not done a RTO lately.
                                                    Dan Downs KCRP

                                                    Comment


                                                      #28
                                                      Yeah noticed landing on 31c MDW with a full -800 a week ago that the airplane came to a stop before 4R. With 40flaps and autobrake 2. Usually that’s a max reverser, flap 40, max auto brake landing in real life.
                                                      Weston Hall

                                                      Comment


                                                        #29
                                                        Yesterday I landed with the 900 in Egmc 6000 ft runway, the aircraft stop at 1/3 of the runway.

                                                        Robert Koolstr.

                                                        Comment


                                                          #30
                                                          Being in the prestigious position of Chief Pilot at “My Oen Airlines” I have simply sent out a Notam that until this issue is resolved on all series of 737NGXu aircraft, aircrews are to conduct “manual braking only”. Autobrakes on all series of NGXu aircraft are to be considered non-operational.

                                                          Richard Bansa

                                                          Comment

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