Hello:Iwould like to understand why descent is starting 40 NM before the actual descent indicated in the FMC.I am doing MMAA MMMX latest has notams and is at 7320 feet. FL is established at 230. I do not think this is normalVersion 3.1 wa s starting early also but no that muchIsthere anyway to configure that in order to havedescent closer to FMC descent?Thanks in advancePedro

>Hello:>>Iwould like to understand why descent is starting 40 NM before>the actual descent indicated in the FMC.Think about it - the FMC predicts the optimal descent point based upon several things: cost index, current altitude, final altitude (as programmed for that flight). The FMC calculated T/D is going to vary from aircraft to aircraft (even of the same type) and from flight to flight. How could ATC possibly know what the FMC T/D is for any given aircraft and any given flight? >Isthere anyway to configure that in order to havedescent>closer to FMC descent?No it can not be configured. But you can always request a Pilots Discretion (PD) descent from cruise. In order to do so, you must have comms. When told to initiate your descent from cruise, note that option 3 is PD. If the PD is granted, then you you can delay your descent until it coincides with the T/D calculated by the FMC. The PD option was added as a new feature of RC4 with the intent to accomodate those flying with FMCs and who would like to fly the descent per the FMC VNAV profile. But as in the real world - you must be prepared to fly as directed by ATC regardless of what you have programmed into the FMC. The FMC is only a tool for managing the aircrafts flight path. -michael

Hello:Thank you for your answer. I agree with that, but I can not imagine that descent is so early.I have been working with all RC since the beginning and this time is much earlier.I know every thing that you mentionned, but still in real life ATC will not make you descend as early as that.Just think for a moment: if you apply the thumbs rule distance = 3 X difference of altitude to descend in my case 23000 - 7000 = 16000X3 = 48 NM and not 98 NM !!!!...so I do not think that is very realistic....of course ATC is not calculating so precisely but it should not be that much....Maybe something to look over the next patch?Pedro

I fly the Level D 767 100% of the time and it has a pretty realistic flight model with an excellent FMC. I find that almost all the time, ATC starts my descent within about 20-25 miles from the TOD suggested by the FMC. I would rather start my descent a bit early rather than a bit late.

>Thank you for your answer. You are welcome.>Just think for a moment: if you apply the thumbs rule distance>= 3 X difference of altitude to descend in my case 23000 ->7000 = 16000X3 = 48 NM and not 98 NM !!!!...so I do not think>that is very realistic....>of course ATC is not calculating so precisely but it should>not be that much....Maybe something to look over the next>patch?Not the next patch but perhaps in future enhancements. I forgot to mention that the RC4 calculation is based on a/c position direct to a point 40nm from destination. The calculation does not take into account the actual distance flown based on waypoints. Therefore, if you show 98 miles remaining until ~40nm from destination based on your filed route of flight but the direct to distance calculated by RC indicates it is time to start down, you will receive the descent instruction somewhat early.-michael

I agree: 20 to 25NM earlier is perfectly OK with me. As a matter of fact I was flying the level D when noticed this situation in this very particular flightMexico city arrival on 5R might disturb a little bit the normal descent procedure but I will use certainly the suggestion made by using pilot's discretion. I also use iap procedures so far the arrival is very goodThanks for both repliesBest regardsPedro

>Mexico city arrival on 5R might disturb a little bit the>normal descent procedure but I will use certainly the>suggestion made by using pilot's discretion. I also use iap>procedures so far the arrival is very goodMMMX 5R is one of my favorite approaches! And I do request full IAP so that I can fly the approach as published. ;-)>Thanks for both repliesYou are very welcome. And thanks for the feedback.-michael

Most FMC's will have "DES NOW" option on the DES page. You can use this function for descents before T/D point.Dave FisherCYYZP4 Prescott 3.2e 478p 800mhz 1mg CPUP4P800SE Asus Motherboard1.5 gig PC3200 DDR RAM 400MHZGeforce Ti 4200/128Maxtor 80 Gig ATA 133 HD x2WDC WD800 80 Gig HDhttp://www.precisionmanuals.com/images/forum/ng_driver.jpghttp://fs2crew.com/linepilot.jpg

>Pilots Discretion (PD) descent from cruise. In order to do>so, you must have comms. When told to initiate your descent>from cruise, note that option 3 is PD. If the PD is granted,>then you you can delay your descent until it coincides with>the T/D calculated by the FMC. HI.I have not seen this Option 3 as yet in all the flights I have made. Is there something I am missing?RegardsDrayton

Hi Drayton,It is only available when Pilot auto-reply is not checked. In other words you have to be acking manually. If Pilot auto-reply is checked the pilot just acks the instruction to descend.Cheers,

Ray,Thanks for the reply, I have now unchecked the Autoreply box.RegardsDrayton

wait a sec here....does that mean if you hand the comms over to the copilot, that you CAN NOT utilize the optional TOD?

That's correct Mike. You must have comms in order to request a PD. You can always select Pause at x miles so you can take over from the co-pilot for long haul flights.Cheers,

I personally think the descent is very good. Maybe in some planes it seems too early, but in a lot of jets it's very difficult to slow down if you just follow the calculated FMC VNAV. Most descents are done in steps anyhow, not one long descent like the FMC will to do without intervention.For example, no matter what altitude a commercial jet is flying into KPHX from the north, it's almost always told to cross BRUSR at 12,000 and even to slow to 250. That's about 40nm north of the airport which is at 1135 feet.