Hi I was wondering if anyone knew if in real life: ATC tells you that you are clearded to descend to ex. FL180 from your crz alt but when they tell you to descend what if it doesn't match up with the green top of descent point on the ND what do you do...descend when ATC tells you to, or ask if you can keep cruising until the T/D? Thanks in advanceTyler

you descend when they tell you to, utilizing the DESCEND NOW selection on the CDU (prior to the TOD) or level change mode (post TOD marker)according to an Alaska Airline NG driver (good freind), actually having hit the TOD AND getting a descent clearence at the same (or close) time - is a very very rare thing in the US.most of calls tend to be 'late' (i.e. post TOD marker).

Assuming you just want to stay at your cruise for the ease of following your FMC plan only, you could request that you maintain present alt until your TOD and you might be lucky & have it granted. On the other hand there might be a very good reason why ATC want you at a lower alt. and your request may not be granted and you should comply asap. Just because that little green circle is showing you where ToD is doesn't mean you have to obey it without question, even though it is a nice feature.dave

I've wondered the same thing for 4 years now. It must mess up any hope of a carefully planned VNAV descent, no? Presumably, most descents in the U.S. must be done by MCP and VNAV is thrown to the wind (no pun intended)?Jonathan

Jonathan,Depends if you were set-up for a VNAV ALT or VNAV SPD descent.If you were set up for the latter - it could be adjusted to suit, simply by changing your VNAV SPD to a higher restraint. Eg. You were planning to descend at 265kts, but you are given clearance later, so you bump up your VNAV SPD to descend at 280kts and you can get down (i.e Vertical Speed) a little quicker, without sacrificing your V/S.Essentially though, if you were given a really late clearance, then LVL CH would be the obvious option - as you can probably imagine the VNAV SPD option is only good if you were notified of TOD a short time (long enough for VNAV ALT to not be an option) after actually passing it.Not sure if it helps - just let me know if you want more detail!

Most ATC descent instructions are given POST TOD. When approaching TOD, you could ask ATC for step descend.

Hi Tyler,A common practice in Europe, or at least Sweden, is that ATC will inform you that they are ready for your descent but you as PIC chose when: "Barnburner 123, when ready descent to and maintain FL230" The ATC people often has a good knowledge of what every aircraft type is capable of.At TOD you just reset your MCP and declare "Center, barnburner 123 leaving FL370 for FL230" and that's it. Neat and simple if traffic allows for it.Now the ATC in FS9 is a different animal alltogether... :+Hope it helps,

Two tricks ATC use at times for the initial descent that I have come across in the States:One is a crossing restriction (which actually is what a STAR is all about when you look at it). ATC will clear you to "Cross Deere at 7,000" or modify by a clearence "At or above" or "At or below". ATC blocks the altitudes but leaves the start of the descent up to the pilot. ATC doesn't care when you start your descent-only that you meet the restriction.Another variant is the "Pilot's Descretion Decent" or sometimes called "PD down to Whatever". There is no crossing restriction BUT ACT blocks the airspace below to the cleared altitude.Both these are nice when arriving into uncluttered airspace, but in a large metroplex expect "hard" clearences such as "descend and maintain.....".The controllers know we are trying to maintain efficiencies by staying high and coasting on in. When an ATC specialist rides in our flightdecks, one thing we try to do is impress upon them how important that is.Tim__757

As Matt said, mostly in Europe, unless there is a descent required due to traffic conditions etc, the instruction will usually be "Descend when ready, FLxxx". This is all fine as long as you meet the descent requirement, which can either be the restriction in the STAR or one that is provided by ATC.eg. "Descend when ready, FL150, level by LOGAN"

Hi Thanks you all for the replies i apprectiate it. now im that much smarter lol thanksTyler