Hi

Looking at the attached pic, groundspeed at MOXEE is 450Kts. At Portal GS is 270Kts.

Now does that mean you are to slowly decelerate from 450 to 270 between that distance, or do you maintain 450 until you're close to Portl, then slow quickly?

I'm working on some descent issues and am wondering if this fits into it somehow.

Thanks,

Mark

Hi Mark,

Those GS are for "planning" purpose, we don't fly ground speeds, ATC doesn't do spacing or assigns GS only IAS or Mach #. So, you will fly IAS or Mach# but you can check your GS against the FPL for evaluation.

 

I see that you are on a STAR from SPNSR, is any speed restriction for PORTL?

 

If is any speed restriction for PORTL you should arrange your speed to arrive (cross) that point at that speed. Same applies for altitude restrictions.

 

It will help a lot if you can share depp/arr airport and the star TMBRS2? I can check the Jeppesen plates for you and give an answer.

no sure if its the same problem i am having i have been flying the fly by wire a320 i work out the descent rate / position by there in game ipad its normally around 110 miles out that it gives but if i start to descend to meet that target p2a steps in and tells me to climb

i have it set like this and have tried to set the descent rate to make the TOD start earlier but not sure i am doing it right 

  

Edited May 18, 20215 yr by Lestat11

The above post is exactly what happens to me, that is, the computed TOD is too far out and when I try to descend to meet a waypoint altitude ATC says to climb back up. If I wait to get a descent command, I really have to hit about 4K  FPS per minute.

While probably not related, I input the same FP into the GTN 750 and the computed TOD is way earlier, resulting in a ‘waypoint missed’ message.

Maybe there is some glitch with that software, I'm not familiar with it.

As a rule of thumb, the TD is calculated similar to 3 to 1 rule. As an example, at FL330 you start descend at about 110 NM to destination, at FL300 at 100 NM, at FL270 at 90 NM, FL 200 at 66. All this is fine if you don't have altitude restrictions at different locations based on terrain and STAR restrictions, then it gets more complicated.

I suggest to try a flight between 2 airports that don't have any significant terrain and don't load any STAR and see if TD is close to what I mentioned.

After that determination we can talk about what kind of rate of descend you will target in ideal conditions. That would be related to your ground-speed.

See what you get as of T/D, I'm curious.

1 hour ago, newtie said:

The above post is exactly what happens to me, that is, the computed TOD is too far out and when I try to descend to meet a waypoint altitude ATC says to climb back up. If I wait to get a descent command, I really have to hit about 4K  FPS per minute.

While probably not related, I input the same FP into the GTN 750 and the computed TOD is way earlier, resulting in a ‘waypoint missed’ message.

4 K it's not normal, something is wrong here.

It's not unusual to see 3500 FT/MIN (when GS is close to 600) at initial stage, and that's quite unpleasant but, 4 K we get very close to an abnormal situation. The more I read into these messages

it looks like an issue with that planing software? Or pilot error?

I find it either gets it dead right or tries to descend me way early, late descents seem a thing of the past (got my settings at 350/1200 for CJ4 after some experimentation - I know they're not accurate, but they work)......

If it tries to descend me early then I respond to the request by requesting an en-route descent - which normally clears me down to IAF at my discretion if I'm not flying a STAR. I also go for en-route  descent if I'm within about 5 miles of my TOD (or if I'm feeling lazy), although with those settings if I leave it then I'm normally descended ok....

I don't know why p2a doesn't just calculate 3 degrees plus x miles (so you can choose how soon you get down) - would save messing about with descent rates..... although guess that could be less flexible..

 

G

2 hours ago, killthespam said:

Maybe there is some glitch with that software, I'm not familiar with it.

As a rule of thumb, the TD is calculated similar to 3 to 1 rule. As an example, at FL330 you start descend at about 110 NM to destination, at FL300 at 100 NM, at FL270 at 90 NM, FL 200 at 66. All this is fine if you don't have altitude restrictions at different locations based on terrain and STAR restrictions, then it gets more complicated.

I suggest to try a flight between 2 airports that don't have any significant terrain and don't load any STAR and see if TD is close to what I mentioned.

After that determination we can talk about what kind of rate of descend you will target in ideal conditions. That would be related to your ground-speed.

See what you get as of T/D, I'm curious.

Thank you for this explanation as I’m new to ATC (which is pretty obvious 😊). Here’s what I’ll do a bit later which is a route I fly occasionally..

KPSP - KSFO No SID out of KPSP and only approach into KSFO, no STAR.

I’m flying the XtremePrototypes Lear 25. I’ll set climb at 3k and descent at 2.5 GS for planning 440 Kts. This removes the variables as you suggested. I’ll let you know how that works out regarding getting the descent call at the appropriate time.

Thanks for the help as I’m enjoying this program and am willing to put in the time to become successful at it.

Cheers,

Mark

Mark,

Out off KPSP going NW you should pay attention to the mountains. I would climb to FL380 that will give you a T/D of 126 NM, add +10 to take in consideration the slow down for 250 KTS IAS @ 10K.

I know nothing about the  XtremePrototypes Lear 25 so for that reason if you have VNAV and is working you should have a T/D at about 130 NM before KSFO and let the autopilot do it. If not, start at 136 NM inbound to SFO with a rate of descend approximately 1/2 of your GS  x (times) 10 +200

So if your Gs is 500, 500:2=250 x 10= 2500 FT/MIN + 200=2700 FT/MIN. As soon as you descend your GS would be less and adjust accordingly.

New GS during descend (for our case) is 400, 400:2=200 x 10=2000 FT?MIN + 200=2200 FT/MIN.

This is what we used to do with non FMS airplanes (in real life), but of course there are different way of doing it.

I still believe that there is a problem with that software but I might be wrong.

If your P2A TOD seems to be coming too late, decrease your planned descent rate in P2A and that will move the calculation out further.  1600-1800 FPM is a good starting place for jets.

During the descent, if it seems you are not getting down soon enough, you can slow your speed which will reduce the distance you are covering as you descend, allowing you to get down without doing a dive bombing run at 4000 FPM.

Dave

Thanks Dave.