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Constantly too late TOD !

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ThomasAH
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 12:01 pm
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vololiberista wrote:
PF3 did exactly what it says on the tin. And did a good job of it too.
PF3 could have issued the descent calls at 16:43 instead of 17:01, so there is room for improvement.
vololiberista wrote:
I would suggest that FL340 is a little high for such a short flight.
I agree with that.
vololiberista wrote:
Pay attention to what ATC is saying. Maintain a listening watch. If the say descend before your TOD then do it.
He did. He did. They didn't.
(And I would assume that in the context of your earlier messages this would trigger a negative reaction with other people, so please try to avoid that)
vololiberista wrote:
If you expect to pass your TOD without anything from ATC then ask them for a descent.
Certainly nobody expected PF3 to wait 18 minutes. Additionally I'm not sure if PF3 would have been happy with that. Will the cruise altitude be recalculated in this case? I think yes, but I don't know for sure.

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vololiberista
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 12:07 pm
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ThomasAH wrote:
Some more observations in Martin's last log:
01/04/2016 16:40:44: 850 - -----------------------------
01/04/2016 16:40:44: 850 - Step Climbs for Waypoint: 3
01/04/2016 16:40:44: 850 - -----------------------------
01/04/2016 16:40:44: 850 -      34000'
01/04/2016 16:40:44: 850 - -----------------------------

01/04/2016 16:42:39: 880 - Checking compliance - Alt: 33660  sWPAlt: 34000  FlightType: 1  ATC_Timer: 0  AltTimer: 0  FSTime: 60159  AptSighted: 0  Handoff: 0

01/04/2016 16:42:39: 900 - TOD recalculated now distance is set to 232 NM
01/04/2016 16:42:39: 920 - ****** Reached TOD ******
01/04/2016 16:42:39: 920 - BPT: 0
01/04/2016 16:42:39: 920 - -----------------------------
01/04/2016 16:42:39: 920 - Step Climbs for Waypoint: 3
01/04/2016 16:42:39: 920 - -----------------------------
01/04/2016 16:42:39: 920 -      15000'
01/04/2016 16:42:39: 920 - -----------------------------

01/04/2016 16:42:43: 700 - Checking compliance - Alt: 33768  sWPAlt: 15000  FlightType: 1  ATC_Timer: 0  AltTimer: 0  FSTime: 60163  AptSighted: 0  Handoff: 0

01/04/2016 17:01:32: 110 - -----------------------------
01/04/2016 17:01:32: 110 - Step Descents for Waypoint: 5
01/04/2016 17:01:32: 110 - -----------------------------
01/04/2016 17:01:32: 110 -      24000'
01/04/2016 17:01:32: 110 -      10000'
01/04/2016 17:01:32: 110 -      8000'
01/04/2016 17:01:32: 110 - -----------------------------

01/04/2016 17:01:35: 860 - Transcript: 'Air India 3205 Descend and maintain Flight Level 240  '
So you reached the TOD calculated by PF3 at 208 NM from the destination (not the 232 NM shown above), but this was before you reached the cruising altitude.
Some things in PF3 are only triggered after the cruising altitude is reached and I think some only at waypoints. It seems PF3 was heavily confused by this situation.

If you could do the climb a little bit faster, or set the cruise altitude a little bit lower, or maybe add some waypoints for PF3 to work with, or maybe fly in an area where PF3 inserts XXX waypoints for control center boundaries, this should already work with the current version of PF3.
Wow, these are many if, ors and maybes, but I assume Dave can find a solution (or at least a workaround) for such situations. But as it is important to not break other parts of PF3 while fixing this, we should let him take the time he needs to make a good decision on how to solve this predicament.
I think the main problem here was that the cruise altitude was set too high with regard to the aircraft's performance. The flight is the equivalent of London to Paris and FL250 is the max for that leg. The VC10 climbs like a rocket in all but the highest temperatures so in my re-run of this fpl I was well able to get to FL340 in time.
Even the fpl ZJSY to VHHX (which is 405 nm not 284nm as in Martin's) my cruise level was only FL240!

So my suggestion to Martin is to knock ten grand off the cruise level and try again.

From Dave's point of view how would he programme a module to compare a fpl with the aircraft's performance in order to avoid this situation of climbing too slowly? And if I was flying a 747 freighter all the way from Europe to the Far East I would certainly have to manually add step climbs to PF3's basic plan. I can't see how PF3 would be able to reprofile a fpl according to a/c weight and performance.

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Dan77
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 12:42 pm
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Maybe throw a warning if cruise is set above a certain ratio relative to length of flight? This value would need to be arbitrary and a warning only, as aircraft specs differ and the pilot would need to make the determination. As far as not reaching cruise by the time one reaches TOD, that could be a problem.

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awralls
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 1:17 pm
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What I'm slightly baffled by is that if the user has set an accurate profile in for the aircraft in use, this could easily be checked against basic climb-cruise-descent speeds and climb and descent rates. It's this element that should be driving the calculation of initial TOC and TOD points and whether or not these are viable. As long as the user has entered it correctly, the data is all there.

In the cases where I've experienced late or non existent descent instructions, it seems that these figures have been either miscalculated or not factored in because I have entered very conservative figures and they are not being respected by the code (that I can see).

If you want to check it out, the log of one of my recent flights is in the thread 'Oceanic Procedures (again)'.

Just a thought....

Andy


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ThomasAH
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 1:19 pm
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vololiberista wrote:
From Dave's point of view how would he programme a module to compare a fpl with the aircraft's performance in order to avoid this situation of climbing too slowly?
He does not have to: If the TOD is reached, issue descent instructions, even if the cruise altitude hasn't been reached yet.
This makes a strange flight, so setting a lower cruising altitude would indeed be better, but at least it results in a workable approach.
Dan77 wrote:
Maybe throw a warning if cruise is set above a certain ratio relative to length of flight? This value would need to be arbitrary and a warning only, as aircraft specs differ and the pilot would need to make the determination. As far as not reaching cruise by the time one reaches TOD, that could be a problem.
Nice idea. PF3 has the climb rate from the preset and rough speed estimates from the aircraft.cfg or PF3 preset, so with a similar calculation as for the TOD, PF3 could calculate a rough estimate of the TOC. If both are too close: Warn. Or if the TOC beyond the middle (or 40% or whatever) of the fpl distance: Warn.
On the other hand there already are flight planners that know the aircraft specs, so they could issue a warning here, too.

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vololiberista
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 1:32 pm
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ThomasAH wrote:
vololiberista wrote:
From Dave's point of view how would he programme a module to compare a fpl with the aircraft's performance in order to avoid this situation of climbing too slowly?
He does not have to: If the TOD is reached, issue descent instructions, even if the cruise altitude hasn't been reached yet.
This makes a strange flight, so setting a lower cruising altitude would indeed be better, but at least it results in a workable approach.
Dan77 wrote:
Maybe throw a warning if cruise is set above a certain ratio relative to length of flight? This value would need to be arbitrary and a warning only, as aircraft specs differ and the pilot would need to make the determination. As far as not reaching cruise by the time one reaches TOD, that could be a problem.
Nice idea. PF3 has the climb rate from the preset and rough speed estimates from the aircraft.cfg or PF3 preset, so with a similar calculation as for the TOD, PF3 could calculate a rough estimate of the TOC. If both are too close: Warn. Or if the TOC beyond the middle (or 40% or whatever) of the fpl distance: Warn.
On the other hand there already are flight planners that know the aircraft specs, so they could issue a warning here, too.
It's not just the basic a/c spec though. Weight and temperature have a significant effect on climb performance. As I said a 747 on a hot day really struggles.

I agree though that if the TOD wypt is reached then a descent call to that of the next wypt be issued regardless of the a/c "actual" altitude.

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ThomasAH
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 1:55 pm
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awralls wrote:
In the cases where I've experienced late or non existent descent instructions, it seems that these figures have been either miscalculated or not factored in because I have entered very conservative figures and they are not being respected by the code (that I can see).

If you want to check it out, the log of one of my recent flights is in the thread 'Oceanic Procedures (again)'.
Andy, your log looks similar to Martin's, except that you have reached your cruise altitude in time and still did not get descent instructions after PF3 logged "Reached TOD".

And what's stange: None of the 54 logs I have kept for bug reports contain this phrase! But this might be due to the descent rate of 1500fpm combined with low cruise altitude (max. FL190) and slow speed (max. 160 knots), which results in TOD distances of 10-30 NM.

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awralls
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 3:02 pm
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Thanks for checking it out, but now it gets weirder... My cruise alt was actually FL250 (I have the FSCaptain log which shows this) and my profile descent rate should have been 500 rpm, not 1500fpm, which would explain why I was not getting any meaningful descent instructions.

Therefore, if the figures you're quoting are from the PF3 logs, something is even more amiss since they don't represent the actual flight parameters I fulfilled.

Andy


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Dave March
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 3:55 pm
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ThomasAH wrote:
Something I found in the logs:
TOD recalculated now distance is set to 236 NM
The length of the flight plan is only 284 NM!
It makes no difference whatever the total distance of the FP is, a TOD is a TOD and the total distance does not form part of the calculation.
Quote:
With a preset descent rate of 1000 feet per minute and a height differential from cruise alt to destination of about 27500 feet, the descent would need about 27.5 minutes.
With speeds between 180 and 280 knots this should only be between roughly 82 and 130 NM.
Cruise was 34,000, FAF altitude was 2,000 so difference was 32,000'

With a GS of about 440 knots 236 miles would be correct. The problem here is the TOD didn't get triggered and it should have done... in this case, due to the short distance, as soon as the aircraft reached TOC.

Currently there's no way of know what GS PF3 was using but I've now added it to the logging ;)

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ThomasAH
Post subject: Re: Constantly too late TOD !
Posted: Sat Apr 02, 2016 5:19 pm
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awralls wrote:
Thanks for checking it out, but now it gets weirder... My cruise alt was actually FL250 (I have the FSCaptain log which shows this) and my profile descent rate should have been 500 rpm, not 1500fpm, which would explain why I was not getting any meaningful descent instructions.
No, FL190 and 1500fpm where my settings, not yours. Your log correctly had FL250/500fpm.

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