I don't know where to post this question since there isn't a forum on just "how to fly". I use Radar Contact with the PMDG 737 ngx. Several times I've gotten the message from ATC that I didn't meet my altitude restrictions and I'm diverted away from the airport to loose altitude. This is after I get a message from ATC something to the affect. "Descend to 11000 feet and slow to 250 knots. I need you down in 30 miles". I don't know how realistic this type of ATC message might be but assuming it is realistic, how would an professional pilot assure that he is at 11000 feet at a point 30 miles from his current position (which likely is not directly over a navigation point). I know I can do some high level math and calculate a decent rate (but it would take me 15 of the 30 minutes to do this ;-). Can the FMC be programmed to follow this instruction and if so how?Thanks for any help or direction where I might find help.

One way is to create a waypoint 30 miles from when you get your clearance and then set the FMC to 250/11000 for that newly created waypoint waypoint.Another way is to create a chart based on speed, rate of descent, and distance traveled and then just monitor the descent.You could also use a range ring. Go to the FMC FIX page and enter /30 from some fix that will meet the 30 mile requirement so that when you reach the range ring you are at 250/11000.Often if you total the distance between waypoints from your current location you can come close to 30 miles then just set the FMC to 250/110000 for that waypoint.As a side not I listen to ATC frequently and I never hear the method RC4 uses. What you normally hear is "Cross [FIx Name] A at or above [Altitude given]. Reduce speed not to exceed [speed Given].In defense of RC4 I always use this add-on and have gotten use to its quirks.Hope this helps you.Don

Same thing, every time (not your fault, and this is a reason why I refuse to use Radar Contact):It's not very realistic at all. I mean, there's nothing against saying it in the real world, but controllers don't because of the question you're asking here. We'd be asking you to make a change on the fly, running quick calculations on the fly. That doesn't make things easy for you, and in the descent phase, pilot are already in a higher work load situation.Most controllers will tell you cross a fix at a particular altitude, using:"Descend pilot's discretion to cross FALKO at 10,000 and 250 knots."To do that, go to the legs page and type in /10000 (leave off the 250, as the aircraft already knows to use 250 max at and below 10,000) at FALKO.In order to save your rear for Radar Contact's unlikely (and borderline unrealistic) instruction, dial your Nav Display distance down so you can see 20 on the hash mark. The next mark out is 30. Use the V/S wheel to put the banana on the 20 hash mark (allowing a few nm buffer because you've burned a few since the instruction, and a few nm at the end to slow down if necessary).Over-reliance on the FMS is going to get you in a world of trouble, but you could also try to insert a PBD (place/bearing/distance) waypoint in front of your current location, which would allow you to get the aircraft to do it using VNAV. This is more work than it's worth, however.Again, because it's so random/unpredictable, real ATC would rarely issue an instruction like this. If anything, we'd just say "descend and maintain 1-1, eleven, thousand, best rate please - Dulles altimeter 30.29." From there, the rate is up to you, but we're asking you to do it quickly (FL CH or similar). That's likely for traffic or we screwed up in giving you a descent earlier, or similar. In any case, we'll do what we need to do on our end to make sure we don't overburden the pilots with weird restrictions.

Edited February 2, 201214 yr by scandinavian13

A descent to be level by a distance is something controllers can use (although maybe not that often) its more likely to be by (or before) a nav point or fix but it can be used at any time really. Its used often when an aircraft is handed over to another adjoining ATC unit ... the receiving unit may want you at X level by X point to maintain separation from their traffic ... traffic that your controller more than likely can’t see depending on many factors. Practicality ... as a ruff example ... at 250kt (GS) you cover about 4.16nm per min (250/60=4.16).... at 250kt you will cover 30nm in 7.21 mins (30/4.16=7.21) ... at 2000fp/min you will descend 14,000 feet in 7 mins (7 (rounded off)x2000=14,000) so you can lose a lot of height if you need to providing you don’t hang about working out the figures ... ok there are alot of factors and every scenario is diffrent but as you know the bottom line is with you if you can make the request or not ... ive found RC does use this type of descent a lot ... guess it something to keep in mind .... especially if your approaching a hand-over close to your desination.In a well equipped IFR rated aircraft you should have all the goodies to assist you which the NGX has in bucket loads, if not some very quick and simple maths should get you out of trouble, the 4nm per min at 250kt is a good one to remember.Hope this helps on the ATC side at least, maybe other members can explain it better as im doing this quickly in my lunch break. RegardsRich

Many things what are being said here is right!But to make it very, very simple........Just use Lvl change instead of decending by VNAV.I use RC4 all the time and never had any probs to be at an ATC altitude 30Nm ahead, if Iuse Lvl change./ Leffe

Edited February 2, 201214 yr by Leffe

I would agree with the above - if you get an instruction as bizzare as that - don't start thinking how to program it in the FMC, just do it. Many pilot think that absolutely everything needs to be programmed in and that's not the case nor is it realistic. Sure a crossing restriction is easy to throw in but a lot of stuff isn't.If I got that instruction, I would put the altitude in and hit LVL CH, then keep an eye on the banana. If it doesn't look like i'm descending fast enough then I'll throw out some drag.

If I got that instruction, I would put the altitude in and hit LVL CH, then keep an eye on the banana. If it doesn't look like i'm descending fast enough then I'll throw out some drag.

What are you going to compare the green banana to?

Just use the "unable to comply" option.

Edited February 2, 201214 yr by gman1986

What are you going to compare the green banana to?

My best guess.

when he says "I need you down in 30 miles or less" there should be an option that says "Unable to Comply" or words to that effect.But yes Radar contact does ask me to come down far to early or late lol.

What are you going to compare the green banana to?

If you set the range at 40, the first mark after the middle mark (20) is 30. You can compare to it.Anyway, i always use the unable to comply also, cause radar contact will always vector to approach and i like to do the full procedures almost all the times. Also, because of that often i get the descend instruction almost miles before the calculated TD.

To make things clearer on that type of restriction, you'll see it in ATC SOPs where the controller must have the aircraft at a particular altitude by the border of their airspace. Normally, the controller takes care of that in the background, meaning, we issue a descent instruction of the "descend and maintain FL250" (instead of adding "pilot's discretion," or "cross X fix at Y") with enough room for you to be at that altitude at the border. I think that's why you'll see VATSIM controllers or RC telling you "this altitude by this many NM," but like I said, we take care of that in the background instead of placing the burden on the pilots.

The real instruction would be something like, "descend to cross 30 DME south of XYZ at 15,000." For the reasons mentioned above, controllers will not issue an instruction that basically says descend to 15,000by 30 miles from you current position. there's no way to use your instruments to comply with it. It should fairly easy to set your ND range to 40 miles and see about where the banana is. One thing you COULD do...say your 50 miles from waypoint ABC, RC says to do the 30 mile thing, well you know 30 miles from where you are would be 20 miles from ABC, so you could go to the fix page and dray a 20 mile range ring from ABC...but that likely wont work since by this point in your flight plan you probably wont have enough distance between different waypoints.

My best guess.

If you set the range at 40, the first mark after the middle mark (20) is 30. You can compare to it.Anyway, i always use the unable to comply also, cause radar contact will always vector to approach and i like to do the full procedures almost all the times. Also, because of that often i get the descend instruction almost miles before the calculated TD.

By the time the jet has an established descent and the green banana has settled down, you're probably ticked off 4 miles.I'd probably start down in LVL CHG if I thought it was going to be close (3-1 rule) and do the simple math (I'm 50 miles from XYZ, so that's XYZ/-20) and plug in a point with the restriction.I wouldn't say "Unable" just because I couldn't do the math. Once I started down, I'd take a look at it and say something along the lines of, "It looks like we'll be unable to make XXX at ZZZ. Do you want the altitude or the airspeed?" Kyle will probably sigh and respond, "Okay, just do your best." ;)

 

By the time the jet has an established descent and the green banana has settled down, you're probably ticked off 4 miles.I'd probably start down in LVL CHG if I thought it was going to be close (3-1 rule) and do the simple math (I'm 50 miles from XYZ, so that's XYZ/-20) and plug in a point with the restriction.I wouldn't say "Unable" just because I couldn't do the math. Once I started down, I'd take a look at it and say something along the lines of, "It looks like we'll be unable to make XXX at ZZZ. Do you want the altitude or the airspeed?" Kyle will probably sigh and respond, "Okay, just do your best." ;)

I was talking using Radar Contact not VATSIM/IVAO.I doesn't care if i can comply with the 30 miles or not. I always choose the unable option. So that way radar contact will ask me to contact approach instead of making me turn 90 degrees until I reach the altitude.But that just what I do.