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TOD question

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Hi Dave

I plan my PMDG737 flights with PFPX and my TOD for a flight from LEAL to LEMH was 65nm before the destination. My cruise altitude according to PFPX was FL220 and G/S 377kts.

In P2A the closest Cruise Alt I could set was FL230 with Plan GS 380kts. I set the Dscnt Rate to 1950FPM which gave a TOD to Dest 68.5NM.

I thought that as the P2A TOD to Dest was slightly greater than the PFPX TOD I would receive descent clearance at 68.5NM which would enable me to easily intercept VNAV PTH but P2A

did not issue a descent. As soon as I passed the PFPX TOD I requested a descent which I finally received and was able to catch the VNAV PTH.

Why did P2A go past the 68.5NM without giving me descent clearance? Am I misunderstanding the use of TOD to Dest figure?

Regards Colin Ackerman


Regards Colin Ackerman

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Colin,

P2A gave you an odd FL because you were heading East.  IF you want ATC to ignore this rule, then check the "ATC Ignores Bearing Based Altitude" option on the FltPln tab of config.

TOD is initially calculated based on planned GS.  During flight, if your actual GS is slower or faster, then a recalculation of the TOD will be made by ATC that might change when you get your descent.  So in this case, if GS was slower, then the descent would have been delayed.

I would suggest reducing your planned Descent rate to 1800 or even 1500.  The recalculation will always use that planned rate, since it doesn't have an actual rate to use.  So your control over getting an early descent clearance is better done with adjustments to descent rate.

Dave

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On 1/11/2020 at 5:04 PM, Dave-Pilot2ATC said:

Colin,

P2A gave you an odd FL because you were heading East.  IF you want ATC to ignore this rule, then check the "ATC Ignores Bearing Based Altitude" option on the FltPln tab of config.

TOD is initially calculated based on planned GS.  During flight, if your actual GS is slower or faster, then a recalculation of the TOD will be made by ATC that might change when you get your descent.  So in this case, if GS was slower, then the descent would have been delayed.

I would suggest reducing your planned Descent rate to 1800 or even 1500.  The recalculation will always use that planned rate, since it doesn't have an actual rate to use.  So your control over getting an early descent clearance is better done with adjustments to descent rate.

Dave

Hi Dave

Thanks for the information, much appreciated.

Regards Colin


Regards Colin Ackerman

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