I fly the Airbus A320 and 21 and i noice that RC allways starts me down a long way before the TOD indicates. RC is reading the FS flight plan which indicates a descent much later than RC..eg, KLIT to KDFW indicates a descent starting at BYP, but RC starts about 20-25  miles before this. I am unable to follow the descent path for the airbus. If i wait after given the PD, i will never meet the required  "start down now i need you level in 30 miles or less" Any suggestions.

     Thanks in advance.

in the real world, you follow the directions of the controllers, not the fmc. if the controllers tell you start your descent, you can do one of two things. acknowledge and start your descent. or request a pilot's discretion descent, and start when you are ready. the fmc is a tool, not a pilot. why can't you do a PD, and start down when the fmc tells you its the right time?

 

there are also numerous postings here on how to set a waypoint at the 40 mile radius, and then the fmc will get you to your crossing restriction at the 40 mile mark

 

jd

oooops, i have been handing the comms to Otto for years, i didn't know i could request a PD at that point, thought i had to do as i was told. Will give it another go this evening. Thanks for your reply JD.

FMCs calculate a constant descent approach to the surface. RC calculates a descent to the crossing restriction 40 nm out from destination which is at11,000 feet (or FL110) or 12,000 feet (or FL120) determined by your arrival direction to the destination airport. RC uses the 3:1 descent profile estimate to the crossing restriction.

 

http://en.wikipedia.org/wiki/Rule_of_three_%28aviation%29

 

Such a crossing restriction is an altitude window providing for orderly entry into the arrival stages of ATC. In the FAA territories at the urging of airlines constant descent approaches (CDA) were experimented with at certain airports with comments from controllers that especially in heavy traffic areas it made it confusing for controllers to maintain a mental image or snapshot of arrivals unsorted vertically. They need to have this image in case of equipment failures essentially putting them in a non-radar state and either way controlled altitude separation is more efficient for controllers to maintain separation.

Thanks for thar Ronzie. What led me to ask the original question is that the Airbus descent has me rather baffled. It does fine in managed mode until about 11000 feet, and then it seems reluctant to descend with any urgency, 200 or 300 feet per minute which is no good to me as i cant get down quick enough. Taking it out of managed mode into an open descent, it has a tendency to overspeed, even with spoilers deployed. Back to the manuals and see if i can work it out.

     Thanks again.