TOD incorrect?

[kneighbour 32]

I have done a few flights now (in the Zibo 738) and each time P2A gets the TOD incorrect by a huge margin. Last night I did a flight from YBTL - YBCS, about 150nm. I was at FL120 and the TOD by P2A was about 20nm from the FAF which required me to be at 3,000'. There is no way I could have descended in time if I followed the P2A profile. I descended via the flight plan in the Zibo and things were ok - but P2A kept on telling me to go back up to FL120. I just ignored it, but it is annoying that P2A does not know the descent profile. I guess I should have request a lower altitude, but the approach did say that I was to descend via the STAR, which is what I was doing. I had a V/s set in P2A at 1500fps, which was about correct and I had it set on 'airliner'.

When I fly the DO-228 (a much smaller aircraft), the TOD seems to be fairly close.

Is there something I can do to make P2A understand that I am flying a jet airliner and not a small commuter? Can I adjust the TOD manually to more accurately match the one computed in the 738?

In this flight I think I was told to contact Brisbane Control like 3 or 4 times while in the cruise (which was about 20 minutes). Each time I did and the system responded. It may have been normal, but it seemed a lot for such a short flight.

[JeB1952 15]

I like to fly the FF 777 and TOD is normally way off until I update the settings for the flight plan.  I am guessing but it seems that airliners like to minimize the fuel and hold the descent until they can just idle the engines and glide down. Although, the 777 wants to drop like a rock and I have a hard time holding the speed down.

I just FIRST keep the ground speed GS updated with what the aircraft is doing and then SECOND I adjust the descent rate to make the TOD close to the aircraft fmc calculation.  I find that it is ground speed that is the big culprit.  I find that for the FF 777 my descent is around 1600-1800 fpm.  Whether what I am doing has any influence on what P2A is doing I don't know for sure but it does make me feel better to have TOD close to FMC.

P2A gives me the 'Expect...' information when it reaches the STAR.   Then I get the 'Descend via...' response which I used to think that I had to begin the descent now.  I have learned that this isn't the case and with TOD close I just let the aircraft descend when it wants and I don't get nagged.

Sometimes no matter what I am responsible to fly the plane so if I want to go down because something isn't right I just request a new lower altitude until P2A catches up.

I am spoiled by P2A to have the information and map visible.  In real world I would have nothing but my ears to receive instructions and act upon them.  The map and flight plan and aircraft information is great for planning but I really think I need to start minimizing P2A.  I think i will be less critical of the discrepancies.

P2A does have problems at times so reporting here is your best approach so Dave can investigate or provide an explanation.  P2A isn't perfect just like ATC is not perfect. 

Have a great flight

 

[Dave-Pilot2ATC 875]

The 4 major determinates of TOD are Cruise Altitude, Target Altitude, Descent rate and speed.  You may need to increase your planned groundspeed to 450-500 or so to get an earlier TOD.  Target altitude is usually somewhere near the FAF altitude, but if  the STAR has "At or Above" altitude restrictions, then the first of these might be the target.

Sounds like your Center Controller radius is too small.  When flying a jet, a setting of 150-200 NM is about right, which would have given you just one Center controller on this flight.

Dave

[kneighbour 32]

Some good pointers. I think I had the GS set to 300kts, which I think was way too slow.

On most of my flights in Queensland, there is (I think) only one Center Controller - and that is in Brisbane a 1000km to the south. There might be one in Cairns as well. It is a big state. A number of regional airstrips don't have tower controllers either. It is not a problem.

[SierraPapaYankee 0]

My TOD problem appears to be the other way around. The controller had me descending WAY too early, & then had me spend the rest of the flight with my a320 flying just above the hills at 4500ft for nearly 20min. 

I had my GS set to 450kts in the flight plan, which was not far off the margin to the true GS I was doing at about 460-470kts. (How are we supposed to know the true speed when programming the flight plan?) 

Apart from that, the program is excellent, although HUGELY overpriced for most of the market of simmers.

[Dave-Pilot2ATC 875]

Be sure your actual descent rate is the same as the planned descent rate.

Edited March 26, 2018 by Dave-Pilot2ATC

[janbergwall01 10]

Or you can use options to adjust the rate of descent. In my case, it's adjusted to FF Boeing 752. And it works fine.

Edited March 27, 2018 by janbergwall01