When instructed by ATC to cross a point at a certain time for sequencing, what is the process that is followed to achieve this? e.g. Is it just a matter of telling the FMS that you want to hit the point at a certain time and the autopilot handles the rest?
Crossing times usually come close to TOD. RTA only works in cruise (in the Airbus and if my recollection is correct the Boeing).
1. Adjust the FMS descent speed to meet the crossing time.
2. Insert a time marker for the crossing time.
3. Manually adjust speed to keep the time marker circle over the crossing point. (Airbus; "Selected Speed". Boeing; "Speed Intervene"?)
4. Make small and frequent adjustments
5. Cross within plus/minus 5 seconds every time
So to answer the question, setting the time in the FMS will not get the desired result. The descent speed needs to be adjusted manually to meet the requirement. In cruise an RTA will work but cruise crossing time requirements are rare in Australia.