Often when listening to ATC (commonly Dublin), when an ATP requests push and start, the controller will reply, "You have missed your pushback window", and/or ask the pilot to call their company or handler to "file a delay" or "update your flight plan with your off-blocks time".
I have two questions about this but I expect the same answer answers both.
- Why is it necessary to re-file the plan, rather than simply activating the flight plan with the actual departure time?
- Why is it necessary for the pilot to change to the airline's frequency, chat them up, change back, and then wait for the electronic flight plan to be updated, rather than talking to the controller directly?