Hi everybody, I have a question?which are the reasons ATC (radar contact in this case) denies a PD descent?I use the PMDG 737, and i would like to use the descent patch calculated by the FMCRegards

Hi everybody, I have a question?which are the reasons ATC (radar contact in this case) denies a PD descent?I use the PMDG 737, and i would like to use the descent patch calculated by the FMCRegards

i think there are twowell, i was curious. so i went and looked it upbetween midnight and 5 am there is a 100% chancearrival runway count > 8 there is a 33% chancearrival runway count > 6 and < 8 there is a 60% chancearrival runway count > 2 and < 4 there is an 80% chance

The other thing to remember about being refused a PD is to keep requesting one. My record is around 7 after which JD (sorry, the controller) finally relented.

Aha,that's interesting.So there is method in the madness!Thanks for the explanation JD.Never thought of that one Ray.I just meekly accept it but do a very slow ROD until the FMC catches up.But you do have to be on the ball as it happens very quickly.

RC uses the three in one rule for estimating the top of descent.http://en.wikipedia.org/wiki/Flight_management_system#VNAV see three degree descent.http://en.wikipedia.org/wiki/Rule_of_three_%28aviation%29RC calculates the estimated three degree descent path to the crossing restriction to determine the TOD. There are real world articles (Airways magazine) regarding how even with the FMC they do a back up calculation because there are certain environment discrepancies that can cause an FMC to miscalculate it.http://www.b737.org.uk/rulesofthumb.htm

RC uses the three in one rule for estimating the top of descent.http://en.wikipedia....ent_system#VNAV see three degree descent.http://en.wikipedia...._%28aviation%29RC calculates the estimated three degree descent path to the crossing restriction to determine the TOD. There are real world articles (Airways magazine) regarding how even with the FMC they do a back up calculation because there are certain environment discrepancies that can cause an FMC to miscalculate it.http://www.b737.org....ulesofthumb.htm

Is there any way of guess where will be the crossing restriction? Knowing that i could set the FMC in the preflight

The crossing restriction is about 40 nm out. My preference is to put a range ring of 40 nm around the destination airport. I then use the descent trend arc displayed in the ND (on Boeings) adjusting V/S as necessary so they do not show beyond the range ring.If there is a waypoint at or just before 40 nm out you could put an absolute altitude on it after the restriction of 11,000 (or FL110) or 12,000 (or FL120) is commanded.To make a range ring in a Boeing Smith's FMC go to the fix page. Enter the ICAO of the airport for the fix label. For the position enter /40 and EXE it to display as a dashed circle on the ND.This is also handy to locate a fix on your flight path near the range ring to place an absolute altitude on your LEGS page.Another handy range ring is 30 nm out at which point you can expect the 230 limit into and on downwind and 210 on base.

Is there any way of guess where will be the crossing restriction? Knowing that i could set the FMC in the preflight

it's only going to be a guestimate at best. depending on the arrival winds, you may get a near side crossing restriction. if the winds are a little different, and a different runway is chosen, you will get a farside crossing restriction. (11,000/12,000 or FL110/FL120 if you are outside the united states, and the transition altitude is below 18000)then your cruise altitude would be used, subtracting the crossing restriction (which will tell you the amount of altitude you have to lose). divide that by 3. that's how many miles rc is going to allow you to travel to lose that amount of altitude. add 40 miles to that.most people do what ron/rob mention - using the 40 mile arc in the fmcjd