Enroute ATC requirements
G'day All,
Just wanting some background information regarding the use of an FMS/FMC when an aircraft is given an ATC "requirement".
As operators how do you manage an ATC requirement given as a "distance" to run eg Reach FL370 by 75 ABC given that ABC is in the legs page of the FMS. Is it easier for ATC's like myself to just give you a requirement by a waypoint as opposed to a distance from the waypoint (obviously outside the area of potential conflict).
Alternatively, how does a pilot calculate when he needs to change level when given a "time" based requirement. eg reach FL350 by time 0324. Time now 0315. Is the V/S functionality involved or is it mentally cacluated??.
Thanks in advance.
DBE...