Mental hangup with RCATC and the BOD point

[Guest klucznik]

Hi Gang, I seem to have a consistent problem with ATC giving me enough time to get down to ATC dictated flight-levels. No matter what I try I still seem to fall short of their requirement unless I sort of dive the aircraft, unrealisticaly, down to altitude. It was always my belief that the airline industry tries to use a descent rate of about 1800/ft-min but I would need on the order of 2500-3000 ft-min to meet RCATC's altitude requirement. As I use FSNav, which has the specific aircraft descent rate info, to export to RC I wonder why RCATC never, never follows the FSNav generated flightplan as far as the point where RCATC issues a BOD command? Not even closely. The BOD on the FSNav flightplan appears to be ignored by RCATC. It seems to me that the only way I could meet RCATC altitude requirements is to follow FSNav's BOD point by requesting a lower altitude from RCATC and, sort of, give up on RCATC hitting it right. Am I missing something here? I wouldn't doubt it. Hoping some of you folks may have some words of wisdom.Good Weekend to you

[jd 57]

the reason i don't use the fsnav information, is because it is not exported to the .apl file. other planners don't have this feature, so i have to go with a "least common denominator" approach on what i can use out of the .apl filei have to try to miss my crossing restriction, and i only descend at 1800 ft/mina lot of the problems may be where the last checkpoint is, whether you start your descent when you get your "pd" clearance, etc.with that all said, i think v3 will go a long way in alleviating the problem you are having.

[Guest klucznik]

Hi JD, I am not sure what you mean by 'PD' and also what checkpoint? It is not clear to me as to your specific uses of these terms. I do look forward to V3 and hope it comes out soon. I seem to only make my altitude restriction if I file for a descent speed of 290 KIAS and use an actual 220 KIAS. Nothing else seems to work for me. The delta descent rate is also a factor. If I increase my rate of descent this numerical speed difference narrows as you might expect. Yet I try to maintain a descent rate of 1800 feet/sec. I'm holding my breath for your release of V3. I still am enjoying V2.2 though.Good weekend and good dinner.

[jd 57]

PD = pilot's discretion. the reason this is important, is you will be cleared through the stratums, and then you will hear "descend and pilots discretion, maintain 15000" for instance. some people don't descend at this point. (bad idea). then when you are told to "cross 40 miles from xxx at 10000, 250 knots", that is another time it is a good idea to heed the "expert" planning the controller is doing to get you down. but 40 miles from xxx, maybe 20 miles from the airport, depending on where the last checkpoint is. see the next note.checkpoint = in this context i was asking about where the last checkpoint/waypoint in the flight plan is. i measure the distance to that checkpoint to determine when to start your descent. if it too far away from the airport on the "nearside", you will be descend way to early. if it is too far on the "farside" of the airport, you will never meet your crossing restriction.

[Guest Scott Campbell]

Which brings up the old note that your last waypoint (checkpoint) should be a VOR as close to the field as possible, although I believe that any waypoint works in V2, including NDBs and intersections.

[jd 57]

correct. some people even put the arrival airport in the flight plan twice.of course all this changes in version 3 :-)in v3 we have the "old crossing restriction" which is what you hear today in v2.2be ready for the "new crossing restriction". this was put in, to handle the situations when the last checkpoint is not near the arrival airport

[Guest Scott Campbell]

And I hear it works really, really well, too. ;-)

[Guest klucznik]

Hello JD and Scott, Since sending my last note in this thread I did mull over, and apparently guessed correctly what you had meant by your two references. My last checkpoint, unfortunately not always a VOR, is always less than 20 nm from the airport, usually 10-15 nm. I just completed a RC flight from KSLC to KOAK and this time I checked both Departure and Arrival NOTAMS and I had no problem doing the MADWIN THREE ARRIVAL at KOAK using the FMG transition. RCATC allowed me to drop from FL310 to FL200 for the FMG--BIFFY segment but would not allow me to drop from FL200 to 8000 feet for the BIFFY to ECA segment. They only allowed me to descend to 10,000'. The suggested altitude for this leg of the STAR is 8000'. So, if I always enable departure and arrival NOTAMS and follow the flightplan altitudes generated by FSNav I end up right on the money. Just can't seem to do that with RC alone even though I am using the same FSNav generated flightplan. Every once in a while RC works out fine but, in general, I do get an missed altitude restriction if I use RC alone. Maybe V3 will clear all that up for me.Cheers

[Guest Scott Campbell]

Blais,With a 10-15 mile last waypoint, it's not surprising you miss your CR. Add the OAK VOR as you last waypoint and you should have no problem making it. When RC says "Descend at pilots descetion, maiontain xxx feet", begin your descent immediately. During the descent, you will get you crossing restriction, "Cross 40 miles from OAK at 10,000', 250 knots". You should already be heading for that altitude.V2 has a very small window in which to get down, and you may need to incease your descent to 2500fpm, but you should make the crossing restriction.Remember, it's all up to having the final waypoint as close to the airport as possible. You also pretty much need to ignore the STAR, as V2 doesn't know anything about those.V3 will allow you to fly a STAR, but you will still be required to follow the controller's altitude assignments.

[CactusDx 0]

Blais,It was always my belief that the airline industry tries to use a descent rate of about 1800/ft-min but I would need on the order of 2500-3000 ft-min to meet RCATC's altitude requirement. No that's not correct. 1800/ft-min is what Microsoft has arbitrarily assigned as a default climb and descent rate in the autopilot mode control panel. Due to this, MS has created the misconception that transport category aircraft are flown by reference to vertical speed and that's not correct. Transport category aircraft are flown by reference to airspeed profiles, not vertical speed.Maintaining V2 + 15 on takeoff with a pitch of 15-20 degrees will yield vertical speeds around 3000-4000 feet per minute. Descending at 300 knots to 10,000 feet will also yield descent rates between 2000-3000 feet per minute. Perhaps try reversing your thinking just a bit: Instead of expecting the radar contact controllers to give you instructions based on your past methods of flying, you may need to adjust the way you operate your aircraft to comply with what ATC is requiring you to do.Keep the questions coming if you're still confused about something and I'm sure someone will be able to get you vectored in the right direction!:-waveMike Collierhttp://fsflightdeck.com/images/RCbeta.jpg

[Guest klucznik]

Hi Mike, I would not wager a bet with you as to the integrity of a VS of 1800 ft/sec while descending but I did not come to that understanding because of Microsoft. I believe I read that in the book "Fly the Wing" by Jim Webb, a long time captain for Eastern Airlines. He used the DC-9 as his basic reference aircraft. I have just pulled the book from the bookshelf and will refresh my memory. In all the RW flights that I have taken in my 68 years I have never had an ear-ache due to the aircraft's descent rate but did experience this problem once while in one aircraft, a Lufthansa DC-10, as it made its descent into Frankfurt. As we were departing the aircraft I did ask the captain what his descent rate was and he said, because of the traffic he was told to descend at 2500-2800 ft/min. I will re-check Jim's book and get back to you, if you're interested.Thanks for your note.

[Guest klucznik]

Hi, Jim Webb of Fly the Wing, and I quote, "Normal descent and even profile descents are predicated upon a rate of descent of 300-feet per nm. The rate of descent required to attain this distance may be determined by dividing ground speed by 2 and adding a 0 or by multiplying ground speed by 5.Page 77 from "Fly the Wing" by Jim Webb, IOWA State University PressISBN 0-8138-0541-41990 Thus I will try to follow this suggestion in the next RC flights I take and see how that works out.Regards

[Guest klucznik]

Hi, I just completed a flight using Jim Webb's Rule of Thumb for descent rates and it worked pretty well. For some reason I had forgotten he goes into so much detail about descent rates at various speeds. Just thought I'd let you know what I tried.Regards

[CactusDx 0]

(edited for spelling)Blais, Glad that seemed to work out ok for you. As a general rule of thumb for descent planning that should work out fine. I always tend to remember as a "quick and dirty" formula that it will take about 3 miles to descend 1000 feet, which is very nearly the same as what Jim suggests in his book. If I'm at FL310 and I have a crossing restriction at FL240 coming up, I'll know to allow myself at LEAST 21 miles for descent. I'd probably go conservative and start down at 25 miles prior to my crossing restriction! ;-)(7000 feet x 3 miles per 1000 feet of altitude = 21 miles)This technique works well when flying aircraft that aren't FMC/FMGC equipped, such as the older DC-9's and 737-200's. When flying the newer FMC equipped aircraft the VNAV functions will often times provide you with higher descent rates since they will climb and descend as fast as practical while maintaining the commanded airspeed profile.Each aircraft is going to perform differently though so minor adjustments may have to be made. Enjoy! New Graphic - Yes/No? http://awva.net/images/Collier%20Pics/RC_Signature-4.jpg

[jd 57]

nice graphic. wish i could do stuff like that. i'm right brain impaired ;-)