OnCourse Software

How does PF3 determine TOD?
More times than not I get instructions to descend about 200 miles too early. This wastes time and fuel, especially if I'm below 10,000 ft and have to do 250 for 100 miles.
I've been ignoring the ATC until I'm closer, but that kills the realism.
I've tried playing with the way points with no luck. It seems that PF3 doesn't use the 3 to 1 rule based on destination distance.

Is there a way to insure that I am told to come down at the optimal distance?
Thanks.

Logs or it didn't happen

I get something like "J-Bird 1608 Descend to 4 thousand at pilot's discretion QNH 1018", so I could use the TOD from my own calculations.

But yes, if your last waypoint is far away from the FAF, the currently released version wants you to descend too early. This will be fixed with the upcoming update.

Thanks for responding...if it's a known issue I'll just wait for the update...When should my last way point be ideally to make sure I come down at the best time?
Thanks again.

I guess everything between 15 and 40 nm should be fine.

ThomasAH wrote:

I guess everything between 15 and 40 nm should be fine.

PF3 could use the rule of thumb formula (distance to destination - 12) x 3. For example you are 82nm from your destination minus 12 to allow for slowing down times 3. 82-12=70. 70x3=210 therefore TOD= FL210.

I would definitely prefer PF3 to use the destination to determine TOD rather than last way point. Destination is less variable than last way point.

mllgrennman wrote:

I would definitely prefer PF3 to use the destination to determine TOD rather than last way point. Destination is less variable than last way point.

PF3 doesn't use the last waypoint to calculate the TOD (that would be a bit silly ). It only uses the rule-of-thumb 3 x 1 if you haven't set a rate-of-descent, if you have we calculate the TOD using altitude, rate of descent and ground speed.

dmarch wrote:

we calculate the TOD using altitude, rate of descent and ground speed.

I get TOD instructions before speed vectors. I just did a flight, and again I was told to come down 240 miles away from destination.
At FL 320, and optimal cruise speed, 3/1 should have me come down at 96 miles away. That's 154 miles of extra time. The airline doesn't like the extra fuel and the PAX don't like the extra time! I still wish TOD was based only by distance to destination.

Is there anything else I can do to get it closer, or is it on the update list?

Thanks again.

mllgrennman wrote:

dmarch wrote:

we calculate the TOD using altitude, rate of descent and ground speed.

I get TOD instructions before speed vectors. I just did a flight, and again I was told to come down 240 miles away from destination.
At FL 320, and optimal cruise speed, 3/1 should have me come down at 96 miles away. That's 154 miles of extra time. The airline doesn't like the extra fuel and the PAX don't like the extra time! I still wish TOD was based only by distance to destination.

Is there anything else I can do to get it closer, or is it on the update list?

Thanks again.

Post your flight plan with the altitudes for each waypoint.

mllgrennman wrote:

dmarch wrote:

we calculate the TOD using altitude, rate of descent and ground speed.

I get TOD instructions before speed vectors. I just did a flight, and again I was told to come down 240 miles away from destination.
At FL 320, and optimal cruise speed, 3/1 should have me come down at 96 miles away. That's 154 miles of extra time. The airline doesn't like the extra fuel and the PAX don't like the extra time! I still wish TOD was based only by distance to destination.

Is there anything else I can do to get it closer, or is it on the update list?

Thanks again.

PF3 DOES use distance from your destination. If you were told to descend it was because the altitude for your next waypoint specified it