Default ATC and top of descent?

[strider 0]

What does FS9 ATC "look at" to decide when to tell you to begin your descent? Is there a "hard number" for an aircraft's default vertical speed, written in one of it's files (.MDL, .AIR, .CFG, etc)? I occasionally have FS9 ATC ordering my descent much too late to be able to make the runway without popping every passenger's eardrums! What drives FS9's ATC to begin a descent when it does? Thanks! Vic

[Mike T 208]

What does FS9 ATC "look at" to decide when to tell you to begin your descent? Is there a "hard number" for an aircraft's default vertical speed, written in one of it's files (.MDL, .AIR, .CFG, etc)? I occasionally have FS9 ATC ordering my descent much too late to be able to make the runway without popping every passenger's eardrums! What drives FS9's ATC to begin a descent when it does? Thanks! Vic

Vic:FS ATC brings you down at ~ 100 nm from the airport almost every time. Unfortunately, depending on your flight plan, that is much too late unless you approach the airport -4000 FPM. May I suggest ProFlight Emulator?

[JerryH 1]

Hi strider,I don't know how ATC determines top of descent. But I almost never have a problem descending on time unless I'm distracted by the copilot or a flight attendant.My procedure is to descend at a 3-degree angle. To keep the descent angle constant, the vertical speed must vary as a multiple of the ground speed. Why did I pick a 3-degree angle? Because that's the same as the typical ILS glide slope and it keeps the aircraft cabin reasonably level so the drink cart is easy to push around.The relationship I use is "Vertical speed = 5.3 times Ground Speed". For example: Descending from high altitude in a B747 at GS = 490 knots, the VS = -2600 ft/min. As the GS decreases, the VS must be reduced to maintain the 3-degree glide angle. Near the airport at GS = 210 knots, the VS = -1100 ft/min.I've installed Ground speed gauges in aircraft that don't display that info. I think the GPS also displays Ground speed. Because winds enter into the calculation of Ground speed, it's not easy to figure out on your own.Anyway, that's the way I do it. It keeps me busy during the descent phase while I monitor the Ground speed and VSI to maintain the correct glide angle. And ATC (usually) stays off my back.Hope this helps.Regards,JerryH

[strider 0]

Thanks Jerry. I appreciate the response but it still leaves me wondering why ATC sometimes waits until way too late to begin my descent. My last flight into RCTP is a perfect example...the only way I could have reached the glideslope would have been to descend the 737-800 at somewhere between 4,500 and 5,000 fpm...not very reasonable. I ended up calling a "missed approach" as there was just no way I was going to make it. If FS9 ATC would leave me alone, I would descend on time on my own, but you know how that is :( . Anyone know what FS9 ATC uses to trigger the beginning of the descent?*EDIT* Didn't see your reply, Mike. It's always ~100 nm no matter what aircraft? I have tossed about using an ATC add-on, one of which you mentioned, or Radar Contact. Still considering that question, however.

[Guest tatest]

Flying IFR in propliners, FS9, I find that ATC does not start bringing me down from 100 NM out. It may be 50 NM, it may be 30 NM. Most of the time, it is too close for a reasonable descent in this type of aircraft, which can't be throttled down to an idle, and has very little IAS headroom, for a dive.I suspect the code for FS9 ATC is working with the TCA definitions, i.e. when you enter the ring that corresponds to your altitude, you are expected start down in a profile that keeps you inside the wedding cake. The TCAs were designed to the performance requirements of post 1950's commercial turbine-powered aircraft, not aircraft that climb at 500 to 700 fpm, and descend in steps at similar rates.

[strider 0]

Flying IFR in propliners, FS9, I find that ATC does not start bringing me down from 100 NM out. It may be 50 NM, it may be 30 NM. Most of the time, it is too close for a reasonable descent in this type of aircraft, which can't be throttled down to an idle, and has very little IAS headroom, for a dive.I suspect the code for FS9 ATC is working with the TCA definitions, i.e. when you enter the ring that corresponds to your altitude, you are expected start down in a profile that keeps you inside the wedding cake. The TCAs were designed to the performance requirements of post 1950's commercial turbine-powered aircraft, not aircraft that climb at 500 to 700 fpm, and descend in steps at similar rates.

I have found the same in my DC3, 6 and 7's. Does anyone know if any of the addon ATC programs handle aircraft in a better manner?

[MarkRey 16]

Strange - I've always found ATC seems to set TOD something like at least FLx3 or so, hence if I'm at fl370, descent starts at 37x3 = 111nm at minimum, most often further out. Only time I ever get <100nm is when flying much lower levels.It can get difficult if the active is same as your general approach direction, but if opposite there's always tonloads of time as ATC levels you downwind, at least that's my experience.

[Guest lgvpilot1]

Strange - I've always found ATC seems to set TOD something like at least FLx3 or so, hence if I'm at fl370, descent starts at 37x3 = 111nm at minimum, most often further out. Only time I ever get <100nm is when flying much lower levels.

That is not a bad rule of thumb to be honest , when Im flying with an Fmc , the default ATC is never far off the TOD that the Fmc displays.Admittedly things do generally start to go bad after that with the default Atc :( But if you use MarkReys Flx3 as a guide then if after 30 or so miles if you dont hear anything , you will have an idea that its all gone wrong and you are going to get vectored off into the blue yonder and get dropped :( Mark

[ronzie 21]

Radar Contact v4 uses the 3-in-one rule of thumb basically:http://en.wikipedia.org/wiki/Rule_of_three_(aviation)where altitude is the (current plane altitude) - (destination elevation).RC also has for the first descent level from cruise issued by ATC a pilot discretion option that lets the user delay descending until reaching the desired position such as that calculated by an FMC. RC also puts a crossing restriction typically of 11,000 or 12,000 feet (or FL equivalent) about forty miles out from destination. If that is issued on an ND that allows it I put a range ring of 40 nm around the airport such as using a FIX definition on an FMC so I know if I require modifying airspeed and/or V/S.Once inside the approach jurisdiction RC lets you do your own nav to the selected runway by requesting an IAP or you can preflight select a NOTAMS option for the departure and/or approach zones that lets you deviate from assigned altitudes.I do not know about FS ATC but RC has an average MSA value for the airport area in which case for a specific approach it might bring you in too high where terrain varies unevenly around the airport. That should be fixed in the new version. RC currently allows the user to implement their own average MSA value for departure and arrival for that session.To work around the FS ATC limitation mentioned consider requesting lower flight levels as you get closer to destination if descent has not been issued soon enough.

[edetroit 933]

My experience is that FS ATC's TOD is normally pretty accurate.......and it is also pretty good on the correct transition altitudes (the STAR's if you select an approach not vectors)What I do is plan my TOD (if not using an FMC with VNAV) and simply ask FS ATC to start my descent early (to which they always comply LOL).Obviously FS ATC will catch up with you as your shallower descent profile matches FS ATC's descent profile.If using an FMC...again simply ask FS ATC for a lower cruising alt (say 10000ft less) at the appropriate time.

[onurksn 1]

My experience is that FS ATC's TOD is normally pretty accurate.......and it is also pretty good on the correct transition altitudes (the STAR's if you select an approach not vectors)What I do is plan my TOD (if not using an FMC with VNAV) and simply ask FS ATC to start my descent early (to which they always comply LOL).Obviously FS ATC will catch up with you as your shallower descent profile matches FS ATC's descent profile.If using an FMC...again simply ask FS ATC for a lower cruising alt (say 10000ft less) at the appropriate time.

This works perfectly for me too. However, I must say that FS ATC is way too late in tailwind situations. :(

[strider 0]

S0...no one knows, exactly, what FS9 ATC looks at to determine begining of descent?It seems someone here would have to know this?All your replies are appreciated...but none of them answer the question?What determines when FS9 ATC begins a descent?(I can't believe I've found the "Golden Question"??) Vic

[mgh 89]

S0...no one knows, exactly, what FS9 ATC looks at to determine begining of descent?It seems someone here would have to know this?All your replies are appreciated...but none of them answer the question?What determines when FS9 ATC begins a descent?(I can't believe I've found the "Golden Question"??) Vic

It's probably hard-coded somewhere in the depths of FS. I wouldn't be surprised, given the age of FS9 and its development, if no one knows the answer now - maybe not even Microsoft!

[hjwalter 25]

It's probably hard-coded somewhere in the depths of FS. I wouldn't be surprised, given the age of FS9 and its development, if no one knows the answer now - maybe not even Microsoft!

My experience with this problem in FS9 is that it's only an issue when there are mountains in the vicinity of your destination airport. The problem can most often be solved by changing the wind direction at your destination airport so that standard ATC will now vector you for an approach to the other end of the runway, where hopefully there are no mountains getting in ATC's way. Changing the wind direction at your destination airport can be done when your (previously saved) flight is opened at your departure airport and then by changing the wind direction and strength (10 Knots) at your "specific" destination airport via the weather drop down menu map etc. When you then (re-) save that flight, this new wind situation at your destination airport will also be saved and will be active every time you re-open that same flight. AI aircraft will now also be using this new wind situation by the time you arrive at your "problem" airport. Perform this procedure for all flights to any airport with comparable problems.Another method could be to increase the ILS GS angle to 4.5 degrees (and sometimes even the ILS range to about 35 Nm) for the runway concerned via AFCAD but I'm assuming here that there are in fact high mountains in your final approach to the "problem" runway. The combination of a steeper ILS GS and the extended ILS range will place the "entrance" to the ILS GS beams at a higher altitude and this quite often solves these types of problems. Don't forget to re-start FS9 altogether after making any changes via AFCAD.Hope this helps a little but some trial and error methods may be necessary.Good luck !!Hans

[Guest rekhraj]

to be safe.....open ur spoilers ABIT until u see a decrease in airspeed...and descend at an average rate of -2500 ft/min..... thats wat i do...slowing down helps...trust me...