ATC descent clearance

[captain_adf 16]

I've been listening to a lot of live atc but mostly approach and departure, so I usually miss the point where clearances are given to descend from cruise. I know the phraseology is something like "[callsign], cleared to descend at your discretion" but my question is, does the crew need to wait for an explicit descent clearance before reaching t/d? If you reach t/d but haven't been explicitly cleared, are you expected to hold or is it expected that you follow your fmc profile?

[skelsey 765]

 

 

does the crew need to wait for an explicit descent clearance before reaching t/d?

 

Absolutely -- you never, ever leave your cleared level without a clearance from ATC.

 

 

 

 

If you reach t/d but haven't been explicitly cleared, are you expected to hold or is it expected that you follow your fmc profile?

 

Neither -- you're expected to continue at your cleared level. Remember, ATC's objective is to keep aircraft separated. They have no idea what your FMC descent profile is: if everybody just started doing their own thing -- it would be chaos.

 

If you are approaching a point at which you'd like to start down, it's up to you to obtain a descent clearance from ATC -- usually a gentle nudge ("Bigjet 123, ready for descent") is enough. However, there may be a reason why ATC are keeping you high: there might be conflicting traffic, for example. If so, you'll normally be told the reason and to expect lower in X miles.

 

Most of the time, however, you'll be descended in good time (often a little earlier than ideal depending on the airspace restrictions), though some places are notorious for keeping you high.