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Guest matey

PMDG 747-400 CDU speed input problem

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Guest matey

Hi, I have the following problem with the CDU of the 747.The FMC calculates automatically the vertical path and also the speed and altitude for each point, but the pilot must be able to make changes in the speed and/or altitude. I am able to input altitude restrictions with the following format:20000 -> upselecting it becomes 20000 ft200 -> upselecting it becomes FL200 (and not 200kn as one can suppose)But if I want to change only the speed for a waypoint it is impossible. The manual (and 747 type rating lesson 4) states that I must input for example 200/ so it becomes a 200kn speed restricion, but the CDU gives me an error message, something like "invalid input".The only way it allows me to input a speed restriction is with the speed/altitude format but thats not a solution because I want to leave the FMC calculating the optimum altitude for each waypoint(without an altitude restrictions).Does anyone have the same problem?ThanksMatey

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Matey,Try entering /200 for speeds. Note the slash before the speed. That way you can change the speed without altering the entered altitude.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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Guest matey

Sorry, but its not the solution. If I type /200 in the scratchpad it becomes an altitude contstraint in this case FL200.The manual and the lesson are very specific on this point it must be 200/ but I always receive the same message "invalid entry"..ThanksMatey

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I've found this happens sometimes as well. My way around it is to simply enter the speed followed by whatever altitude is currently displayed.


Mike Roth

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Guest matey

>I've found this happens sometimes as well. My way around it>is to simply enter the speed followed by whatever altitude is>currently displayed.Yes, but as I stated above, this method is far from perfect, because the FMC is constantly making predictions for the altitude of each waypoint depending on the aircrafts current speed and altitude. So the computed altitude for a given waypoint changes constantly (not much but changes) so giving the FMC an altitude constraint without really needing it not a good way to manage the vertical path.Thanks anyway Mike ;-) (cause finally that would be the only solution, I suppose)

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Guest matey

So , finally, it appears to be a bug, or maybe its caused by some misconfiguration..

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I don't think you can simply enter a speed at a waypoint fellas. I'm pretty sure it has to be with an atltidue restriction of some sort. Qavion, a 744 pilot or someone sure of this will be able to confirm/correct this - but I am reasonably sure this is the case.Simply open the MCP speed window, or maybe enter a speed restriction on the VNAV CLB/DES pages if appropriate.CheersRudy


Rudy Fidao

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The speed VNAV uses is determined by the descent speed in the FMC on the VNAV descent page. Normally this is ECON speed and is dependant on the Cost index entered. If you want to cross a waypoint at a certain speed then you need to enter an altitude against it. One way you could do this is to look at what alt the FMC has calculated to cross the waypoint in question at and then enter it as a speed/alt. For example if it was going to cross at 285/11645 and you wanted to cross at 250 kts then you could enter 250/11700. The speed will remain at this until the next spd or spd/alt constraint. Or you could enter 250/12000B The B standing for below. The speed will change to 250 kts below 12,000 ft. You can also use the SPD RESTR (speed restriction) box on the VNAV DES page as well.Cheerssteve


Cheers

Steve Hall

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Guest matey

Thanks Steve, your suggestion is the best one, I also thought about that example as the best solution because 250/12000B would not be in conflict with the FMC calculated altitude (11645 in your example). But I still have two doubts about speed change in LEGS page.This weekend I have reinstalled FS2004 v9.1 and all Boeing PMDG aircrafts with all the updates available till now. 1.- PMDG 737 FMC DID ACCEPT SPEED CHANGE ONLY in the LEGS page. For example for the descent below 10.000 ft it gives me a constant speed of 240 kn for all the waypoints. I can change it to 180 for example, typing 180/ not affecting the altitud in any way (altitude remains in small font).2.- On page 35 of PMDG 747-400 Type Rating Course 4 the author tells us to input 210/ in order to slow down the aircraft for the approach. Could he be wrong? An example of this page follows in image format.ThanksMatey

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Descent below 10,000 will give you 240 kts for all subsequent waypoints as this is below the 250/10000 ft speed transition altitude (Look on VNAV descent page). The FMC uses 240 kts instead of 250 to give a 10 kt buffer.No Matey the type rating course is correct. If you look at the legs page you will see that the altitudes are in large font. Typing 210/ and putting it over the altitude puts the speed in at the beginning of the large font altitude. In the real FMC you can put a speed at the final approach altitude, which the course says you cant. I do not know why it cannot be done in PMDG. It is only a small issue anyway.CheersSteve


Cheers

Steve Hall

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Guest matey

So you suggest there was an altitude restriction (altitude in large fonts) before the author puts 210/ and 180/ respectively, and thats why the FMC accepts the speed restriction. I also thought about that for a while, but I have not tried it since I have still not flown that course.So, in other words you can put a speed restriction to a waypoint only if:1.- you also put an altitude restriction (speed/altitude).2.- if the waypoint allready has an altitude restriction (the case of sid and stars).If thats so, I am not 100% sure but I haven

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>So you suggest there was an altitude restriction (altitude in>large fonts) before the author puts 210/ and 180/>respectively, and thats why the FMC accepts the speed>restriction. I also thought about that for a while, but I have>not tried it since I have still not flown that course. The fact that they were approach waypoints leads me to believe that they would have already been in Large font. Approach waypoints that have an altitude coded against them are in large font.>>So, in other words you can put a speed restriction to a>waypoint only if:>1.- you also put an altitude restriction (speed/altitude).>2.- if the waypoint allready has an altitude restriction (the>case of sid and stars). Correct.>>If thats so, I am not 100% sure but I haven


Cheers

Steve Hall

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Guest matey

> From a VNAV perspective the legs page is primarily for>entering altitudes. When an altitude is entered a speed can be>set as a consequence of that action. It needs to be registered>against a large font. The speed portion of VNAV is primarily>set on the VNAV descent page. If you want to know the altitude>you will cross at then create a waypoint a mile or so back. ie>.XXXXX/-1 This will be close enough to let you know the approx>alt at your waypoint. You could also put the waypoint you are>concerned with in the fix page. This should give you a>crossing alt at the waypoint (Not sure of this is modelled in>PMDG. It is in RW aircraft).I don

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Guest Tom Meyer

I realized tonight why I thought you should be able to add a speed to a non hard altitude constraint. In the LDS 767 you can. Now, I'm not sure if that is real world behavior. If it is, that's kind of strange that you can add do it in the 767 and not in the 747.Any thoughts?

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