PMDG Captains, Crosscheck your SPEED RESTRICTIONS | Real Airline Pilot
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- Опубліковано 2 вер 2023
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Thanks so much for the explanation and helping us to improve our ability to make our sim experience more realistic and enjoyable. And yes, I was one of those that would just ignore the message. Clearing it just resulted in it populating again.
Super clear, txs
Thank you so much for these tutorials! Much appreciated!
Ohhhh, that makes sence. I was wondering about that for quiet a time now. Thanks for that helpful information
I think the UNABLE XX KTS AT YYYYY message merits some more explanation. Many simmers simply are taken aback when they see this as if something will break. Nothing will break. One short (bad) option is completely ignore the message. The best thing however is to actually understand WHY this very useful message appeared and take action from there.
The mathematical answer is called "monotonic" climb and descent. This is what all FMC's in the universe do. That is, a FMC will only speed up in climb and slow down in descent. The FMC will select for its schedule the most restrictive speed between ECON speed (cost index) or SEL SPD (pilot entered), transition altitude speed (e.g. 250/10000) and next waypoint restriction. Below the acceleration altitude as in the example shown in the video there is also V2+10. An FMC will stick to the most restrictive speed and then in climb go to the next higher and so on. In descend again the most restrictive speed and then the next lower speed and the next and the next....
Example : Lets us say your ECON climb speed is 300, you have 250/10000 and there is a waypoint with 230 knots at 15000. VNAV will target 230 until passing that waypoint (at 15000) completely ignoring till then your 250 below 10000 and 300 above 10000. Now if this waypoint is at 260/7000' you will see the UNABLE message since the most restrictive speed is 250 till 10000.
Another example : let us say your cost index is 6 (Ryan Air) meaning your ECON descent speed is 245 knots. If you set 250/10000 for descent it will be ignored because 245 is more restrictive than 250 already. If you have a waypoint at 280 knots you will see the UNABLE message. Because of "monotonic" descent the plane cannot start descending at 245, speed up to 280 then back to 245. Cannot happen. Result UNABLE 280 AT YYY. In plain English : the rest of your FMC setup does not allow this speed, do something or dont.
So armed with this knowledge of "how it works" what can you do. Check the chart. In European airspaces most of those restrictions are MAX for example 280. Meaning you can perfectly go at a reduced speed less than 280. As explained in the video simply enter 280B/ and thats it. HOWEVER, in some airspaces (e.g. typical US based STAR) when it says 280 it means 280 not at or below. The controller expects the plane to fly at this speed for traffic separation within a narrow margin. In this case if you are restricted by your ECON SPD then either increase your cost index (this will increase all speeds) or better go to the DES page and edit your "open" descent speed. E.g. write /280 and upload to LSK 2L. That solves the problem. IF you see a waypoint with 250 located at say 8000 and you MUST fly at 250 then edit the 240'/10000 restriction to 250. In short always manage your most restrictive speed.
Final note : this is a 737 message that you will not see in Big Boeings because there it is assumed by default that any speed restriction is "at or below". As if you have a B next to it.
I hope true understanding rather than simply monkeying out a fix will help you make always the proper decision.
Thank you!
oh yes! very useful! i had many times this issue and i dint know what was the reason for it. I end up ignoring it but afterwards the message appeares again! very useful tipp! Thanks!
ahh, thank you for explaining it and especially the reason behind it. i just bought the 737 a couple of weeks ago and run into this issue. now while i saw how to fix it with entering below or above, i didn‘t know, why this was happening and came to think it might be a quirk of the plane itself rather than a coding issue.
danke und schönen sonntag!
Thank You. Excellent
Thank you I always see this.
Nice!
Didn’t know that, don’t do it but will pay attention and use it in future, thanks
Interesting again. But I am a little proud of myself. Reading the charts of Navigraph and always trying to fly as real world as possible, I solved it myself. But now I know I did it the right way. :)
I am surprised however that it is not corrected by the Airac of Navigraph. I understand that inserts other data?
I figured it out by myself shortly after I start flying PMDG 737 in MSFS after ZIBO. However, it's a big surprize for me that 777 does not have it. How is that even possible and how are pilots supposed to fly on them without it? Keep it exactly 210 or somehow manually predict what speed the airplane is able to achive at this point instead of relying on the FSM? That's weird.
Can I request a tutorial how to react when there is a tcas warning
Airbus don't seem to have above or below speed constraints which has always confused me.
I have a 736 and I have a problem with stall shaker test. When I press the buttons it doesn't work. Any ideas why ?
Hey, can u explain why Every time I start engines and then turn my packs on again I get a message on my ac panel, and I see “zone temp” in amber can u explain how I can fix this and prevent it from happening? Thanks!
When a chart says to descend via Mach then 280 at transition, and the FMC is predicting a slower speed, will those messages pop up as well prompting you to manually change the descent speed in the DES page? I have just experienced this today. Cheers!
It would probably give you an "UNABLE xxx at yyy" message, so if you got a chart like that best practice is to modify the VNAV DES page to include those speeds as standard speed.
Never had this for departures but have many times on STAR's. I also get cases when my descent speed is below an exact speed constraints (i.e 256 knots descent speed but approaching a waypoint with a 280 knot constraint). So I then change my descent speed to meet that constraint. Is this the correct procedure?
Check the charts ;)
@@piotrkuler683 I do, I modify descent speed before T/D. I just wanted to know if that was the correct way to do it. The only other way I can think is to descend at ECON then increase speed just before constraint which makes little sense
Hi emi when i fly into ksfo and they say at 270 and the pmdg says unable what can i do.
Modify the plan until you can do it. First determine what causes the message. Too much energy? Too little?
Then find a solution accordingly.
@@A330Driver thank you, normally its too little so i could increase speed at other way Points to maintain it.
Hey, im first nice