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Guest dutees

ATC descent request

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Guest dutees

Hi there. I've been using the PMDG 737 package for some time now but have only recently bought Radar Contact 4 to run alongside. What an experience!! However, I would like some help on a request from ATC as I can't find any advice about it in the 737 operating manuals.I am flying along at 36000 feet and ATC asks me to DESCEND NOW to 16000 feet and wants me to be at that level WITHIN 30 MILES.How do I go about entering this request into the FMC to get the aircraft to comply ? I descended manually (FLCH) but when I had finished the flight, I had a "gentleman" come on to ask me about a height violation so I don't think I got to 16000 feet in time.Hope someone can help an old but very enthusiastic pilot !!Regards,

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Hello,I use the 3 in one rule when asked to descend to a specific altitude/FL. In short when flying at FL360 and asked to descend to FL160 with a GS of 480:*Drop the zero from 360 and the target altitude of 160. 36 minus 16 makes 20. Multiply 20 by 3 makes 20x3=60 plus 10 makes 70nm. So the TOD is 70nm.*GS is 480 divided by 2 makes 240 and add a zero makes ROD 2400 ft a minute.So we have to start the descend at 70nm from the target with a rate of descend of 2400 ft a minute (Using VS).But if you have to be there at 30 nm you have to increase the ROD and watch the green arc at the primary flight display. If the speed increases to much use spoilers during the descend.You also can reply to ATC with "negative, unable to comply;) when the pax are finishing their dinner.As an alternative to increasing the rate of descend (with VS) a tip from a real 737 pilote: if you increase the speed during a descend you will increase the rate of descend and if you decrease the speed during a climb you will increase the rate of climb. Handy when ATC aks you to expedite your climb of descend.Hope this (is correct) and helps.Regards,Another mature;) flightsim addict from EHAM.

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That is a pretty tough ask......20,000ft in 30 miles. First of all take a note of the distance to the next waypoint and then get going down.......and quick, full speed brake and wind the airspeed right up. A normal descent profile is 3 times the height to lose/1000 and is the distance required in miles you need to conduct the descent. In your case you would need 20 x 3 = 60nm and you have to do it in 30nm !!! I will assume you are tracking to a waypoint of some description. If the waypoint is more than 30 nm away then deduct 30 from this distance. If it was say 100 nm away then this would equate to 70 nm. Go to the legs page and select the active waypoint into the scratch pad (press the top left key). Type in /-70 and then press the top left key again. Have a look on your ND to see that it appears on the map OK and if you are satisfied then press the illuminated EXEC key. This new point you have created will now be the active waypoint. Type in 16000 and select the top right key. This will now create a path from that point. Do not delay commencing getting down as you will be eating up valuable descent miles otherwise. The best option for you is to use FLCH (VNAV will struggle), speedbrake and a high airspeed to help you get down. As long as you have 16000 set in the altitude window on the MCP panel you should see a green arc on the ND. That arc tells you where along track you will be 16000 at your present rate of descent. It is a dynamic indication and not based on planned VNAV info. You can make adjustments accordingly to get it sorted nicely. I am not surprised you had a altitude violation!!!CheersSteveCheersSteve


Cheers

Steve Hall

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Guest wisborg

What I'm doing (I only have the B747, so possible there are some differences) is the following.Using Radar Contact, I know that they will ask me to be at 11,000 or 12,000 feet around 40 miles from the airport (assuming the airport is not to much higher than sea level - I think it's around 15,000 or 16,000 for e.g. Mexico City). So when I'm reaching cruize level I add a waypoint in the same manner as Steve described a little more than 40 nm from the airport (or the VOR sitting next to the airport, if I have that included in the flight plan). Typically I chose 43 nm, so I don't get in trouble if my descend is a little delayed, and if there's a speed restriction involved as well, if can be useful with those extra miles to get the speed down.Then I put a speed restriction of 280 and altitude restriction of 11,000 for that new waypoint, forcing the FMC to recalculate the TOD to a point where I can make it down in time without trouble, including slowing the plane down to 280 kts. I know that the speed restriction enforced by Radar Contact is 250 kts if the crossing restriction is 11,000 ft, but I warn the FMC about this by putting a 250 kts restriction at 11,200 ft on the descend page.In this way I can do the descend without problems and without needing to fiddle any more with the legs or descend page - I just need to set the MCP at the appropriate altitude. If the crossing restriction is 12,000 ft I do get down a little early, but it's really just a matter of around 1 minute or so flying at 12,000 ft.I don't know how real world pilots deal with these kind of issues, and there might be better ways of doing it. However, I find it a quite convinient way of preparing the descend./ Jesper

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