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Alex Kulak

PMDG not stopping fast enough

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Hi my PMDG 737-700 is not stopping fast enough. i came in with an ias of 145 flaps set 30degrees.

autosbrakes set to 3 on a 6446 runway at chicago midway. when i touched down spoilers went up and autobrakes were enabled. the autobrakes didnt go down until my nose wheel touched the ground. by that time i was 3/4 down the runway. then the autobrakes went on and off and i did not bounce. can somebody please help me with this problem.

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Did you use reverse thrust?  You nose wheel should have touched down well before 3/4 of the runway.  Check your landing technique.

 

Rob

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Did you use reverse thrust?  You nose wheel should have touched down well before 3/4 of the runway.  Check your landing technique.

 

Rob

 

It has to be his technique, also he may be trimmed way too nose up.

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can somebody please help me with this problem.

 

Do the tutorial flights.  You need to learn the basics.  Does your reverse thrust work?

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no i the trim is good i did the tutorial flights. the nose gear came down well before 1/2 the runway. then the auto brakes came on. then they went off and on. the reverse thrusters also didnt reverse till the nose gear was on the ground i come in ILS never RNAV or VISUAL

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Sounds like you are coming in nose too high, so it's your landing technique.  Reverse thrust can come on before your nose wheel touches down if you've activated it.  Check your installation.and run the approach and landing tutorials again.

 

Rob

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The landing speed is correct ?  I mean, sometimes my landing speed, depending on the load, runway conditions etc... is around 136 knots.

 

A correct landing speed and an earlier nose down attitude will help a bit.

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I can stop the 737-700NGX on a 6000 feet runway with a 50 per cent fuel load without using the thrust reversers, so something is indeed amiss. The only difference is that I use manual brakes. I think the approach speed is around 135 knots.

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I can stop the 737-700NGX on a 6000 feet runway with a 50 per cent fuel load without using the thrust reversers, so something is indeed amiss. The only difference is that I use manual brakes. I think the approach speed is around 135 knots.

 

I always had the impression ( maybe wrong, because I am only a simmer ) that reverse thrusts on the NGX are " too gentle ". Am I correct or is it just a wrong perception of whom is not a real 737 pilot ?

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The effect of reverse thrust in terms of braking in real life is pretty much negligible, at least on a dry runway.

The effect of reverse thrust on noise however, is far less negligible. That's why people assume reverse thrust is an awesome stopping power, because they hear it, a lot.

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I always had the impression ( maybe wrong, because I am only a simmer ) that reverse thrusts on the NGX are " too gentle ". Am I correct or is it just a wrong perception of whom is not a real 737 pilot ?

Reverse thrust has no effect on stopping distance when combined with Autobrakes. Even if manual braking is used the amount of stopping power from reverse thrust is still small but most effective whilst still at high speed during the rollout.

 

Regards

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Don't the autobrakes try to maintain a predefined deceleration rate? So reverse thrust should be largely irrelevant?

 

 

 

EDIT:

 

Thanks, Rob! :lol:

Yes correct :) Reverse thrust saves on brake life since the Autobrakes have to do less work, also keeps the brake temps down.

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Reverse thrust has no effect on stopping distance when combined with Autobrakes. Even if manual braking is used the amount of stopping power from reverse thrust is still small but most effective whilst still at high speed during the rollout.

 

Regards

 

I didn't get it. Do you mean that reverse thrusts effectiveness is directly proportional to the speed on the runway ?  I thought the reverse effectiveness should be always the same from when applied to around 60 knots when disengaged.

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No, reverse thrust has more effect whilst the aircraft is at high speed, the slower you get the less effective it is.

 

In the real world at least..

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Yes correct :) Reverse thrust saves on brake life since the Autobrakes have to do less work, also keeps the brake temps down.

 

 

Looking at it the other way round, autobrakes save on engine wear&tear and keep the noise down.

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Looking at it the other way round, autobrakes save on engine wear&tear and keep the noise down.

Hehe true :) Qatar airlines don't even use reverse thrust on rollout in Doha on the Airbus fleet

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I didn't get it. Do you mean that reverse thrusts effectiveness is directly proportional to the speed on the runway ?  I thought the reverse effectiveness should be always the same from when applied to around 60 knots when disengaged.

 

Basically, when you land with autobrake armed and activate reverse, braking force created with reversers is strong enough to achieve preselected autobrake deceleration value, so little or no braking is provided by wheel brakes. As you are slowing down, braking force generated by reverser cannot achieve preselected autobrake deceleration value anymore, so wheel brakes kick in to help reversers to achieve preselected value.

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With carbon fibre brakes, reverse thrust will hardly be used, except for those rare circumstances when (no, I don't really know about that stuff; just following discussions :ph34r:)

 

- even carbon brakes get really hot (high weight/speed, short runway)

- short turnaround time (for brakes cooldown)

- noise abatement procedures NOT prohibiting rev thrust.

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Hehe true :) Qatar airlines don't even use reverse thrust on rollout in Doha on the Airbus fleet

 

At that runway they do not need to brake at all. Aircraft will stop eventually.  :lol:

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I have been checking this out on the internet, and there seems to be a considerable amount of disagreement regarding just how effective thrust reversers are. I am certainly no expert, but I would be surprised if the effectiveness of thrust reversers at high speeds was not significant.....or are we only talking about how much extra stopping power they provide when used with the brakes?

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I have been checking this out on the internet

 

Even if that's true, I wouldn't include that in your posts.  It immediately makes me think "watch out guys, we got an internet scholar here!!!"

 

...and in this case, it proves to be true.  Details follow:

 

 

 


I am certainly no expert, but I would be surprised if the increase in stopping power at high speeds was not significant. To be honest, I have seen a LOT of landings at Manchester and Edinburgh airports over the years (the two airports that I am most familiar with), and thrust reversers appear to be used over a large percentage of the entire rollout in a large number of cases

 

The problem with reading things on the internet is that you have no idea as to what their credentials are, and, unless they specified the type of thrust system, their commentary may be invalid.  Certain thrust systems actually reverse the thrust, throwing it forward, which is where the name came from.  Others simply divert the thrust in a direction other than out of the rear of the engine to reduce thrust below idle.  Obviously, the thrust system throwing the thrust forward, and more forcefully so, will be more effective than simply diverting it away from the rear of the engine in general.  You can't categorically say they're all really effective, or not effective.  That's like saying all props are good a climbing, or all props are very effective brakes on the idle stop.

 

 

 


In my book, that does not equate with "negligible".

 

I think his quote was more aimed at the fact that the plane is going to stop in X feet on a dry runway either with TR or without.  Autobrakes, being so prevalent, set a deceleration rate and maintain that.  It will maintain that with or without TR.  The difference between its use, and lack of use is therefore negligible.

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It differs by company how to deal with reverse. Some use them all a long till 80kt, others only idle as SOP depending on rwy lenght and weather. 

 

John

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You responded too quickly, Kyle! I updated my post several times because I wasn't happy with what I had written.

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