I can only speak for our operation, but typically for the same flight number going from A to B every day it'll be the same route, or one of 2-3 depending on weather/wind. The actual path is calculated with planning software. The planned runway at each end (and thus planned SID and STAR) is based on seasonal patterns. On the day, of course, winds change, so the flight plan might say we are using 07L and its STAR but in the FM we put in 25R and its STAR. The published flight plan is not changed with the actual STAR, but the flight folder software tracks which runways and STARs are used and we can see what is likely based on past flights. And of course, once we get closer to the destination the runway and STAR might be different from what we expect, and the runway could change multiple times during the descent. But that's all tactical.
We don't make our own flight plans and only very rarely would we ask for a change in the actual route. There might be a volcanic eruption or serious weather that the planners have not been conservative enough about in our opinion. But again, very rare. In almost all cases any deviations for weather or other things are decided on tactically while in flight.
The one big number we decide on is fuel, and the captain can indeed request more fuel, typically if we expect extended holding. The company does not really have a mechanism to refuse such a request. We tell the fueler how much we want. The fueler does not then check with planning or dispatch if this is ok. He just loads it on. That being said, fuel requests are tracked, and if a captain frequently takes on a few extra tons "just because" he might find himself having a conversation with the chief pilot. Carrying more fuel costs money, so the fuel figures are rather "optimised" and the company accepts that there is a certain risk of diversion with the planned fuel.
Proceeding to give you way more detail than you probably wanted, chronologically the process is something like this:
- Several hours before departure, a preliminary plan is drawn up by the planners using software tools. This contains an estimated zero fuel weight and estimated trip and total fuel.
- 2-3 hours before departure, the flight plan is published to the flight folder app, along with all the ancillary documentation (NOTAMs, METARs, RAIM predictions, weather charts etc...). We can now review it.
- A new flight plan version is published if the zero fuel weight changes beyond certain thresholds. A ZFW change will always involve a fuel number change, but could also involve a planned flight level change. An aircraft change would also result in a new version.
- 60-70 minutes before departure, the crew reports to dispatch (at home port) or the aircraft (at an outport) and we do a dispatch briefing. (If on a turn, you simply download the flight plan while sitting in your seat.)
- We make a preliminary fuel decision based on the estimated zero fuel weight, typically accepting flight plan fuel but sometimes taking more, and give the fueler a standby fuel figure. This standby figure is somewhat under what we expect the final to be, so that if our zero fuel weight decreases, we can decrease the final fuel figure.
- We enter the estimated zero fuel weight and preliminary fuel figure in the FM so that it calculates performance correctly. We also use the preliminary takeoff weight for a preliminary takeoff performance calculation.
- 35-ish minutes before departure, the flight is closed, and the cockpit printer chugs out the final zero fuel weight, received via ACARS.
- We make a final fuel decision, allowing for changes from the estimated to the final zero fuel weight, and give the fueler the final figure.
- We send the final fuel figures off via ACARS. The loadsheet is produced using these numbers.
- Once the fuel is onboard, we check that we got what we asked for within a certain tolerance, and that the distribution is correct.
- The cockpit printer chugs out the preliminary loadsheet. We check it and enter the final weight/fuel/CG numbers in the FM. We also revise the takeoff calculation with the final takeoff weight and enter the resulting performance numbers in the FM.
- Once all the pax are on, the traffic guy comes in and tells us that the final loadsheet is on the way. He confirms the final pax number, which may have changed if someone was offloaded. He leaves the plane and the door is closed.
- At some point before takeoff, we receive the final loadsheet. We check it and make any changes in the FM. We accept the loadsheet via ACARS. This must be done before the "before takeoff" checklist.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo