A flight plan must be filed for each airline flight. This requires a lot of work, starting with the flight dispatchers for the airline you are flying on. They do all of the flight planning, will be flight tracking your flight, and be the point of contact within the respective airline operations for your pilots. The airline dispatcher is also responsible for the safety of your flight, besides the Captain. These days, almost all plans are computerized which makes the job somewhat easier. Yet, there are many variables that go into this plan and there is a constant balancing act among the variables. These include the origination, destination and enroute weather; scheduled flight time, route of flight, fuel required, weight of the aircraft, and any maintenance items that might have an operational impact.
The dispatcher must juggle all of these variables to optimize each flight in terms of safety, being on-time, and being most efficient in terms of fuel. The dispatcher will usually work up the flight plan and associated paperwork about 1.5 to 2 hours before your flight is scheduled to depart. There will also be an initial talk with the load planner to determine how many passengers are booked and if there is cargo to be taken. There are several sections of this plan including flight weights, times, and engine parameters, weather, runway analysis, Notams (Notice to Airman), altitude winds, and applicable aircraft placards (inop items, systems, etc.).
The Captain of your flight will then print or have printed this flight plan, it can be up to 30 pages long! While there are many sections to check on this flight plan, and each Captain is different, the following items are among the most important:
1) route of flight/time enroute(with fuel burn) - what route has the dispatcher planned for. Many times there is a standard company route that goes from your origination point to your destination. Or there can be several, however the route selected is, in the dispatcher's opinion, the optimum route in terms of weather, fuel burned, and winds. This requires looking at aeronautical charts, especially for an international flight. Obviously the best case scenario is the route that gets the flight on time to destination with the least fuel burned and avoiding bad weather and strong headwinds (which increase fuel burned and time enroute).
2) weather- what is the weather where you are now, enroute weather, and destination weather? If the weather is not too good at your destination, an alternate airport must be listed and the corresponding fuel must be added to be able to get to that airport. If there is a chance of enroute thunderstorms then that must be taken into account. Enroute weather also includes the chances of reported turbulence at altitude and possible mountain wave activity if flying over mountainous terrain.
3) fuel over destination (and alternate if applicable) - what is the estimate fuel that the dipatcher has you arriving over destination with? Does it take into account all the forecast weather factors? And based on experience, can you expect delays and slowing on arrival, thus burning more fuel? Burn fuel enroute is predicated on the flight level and winds expected at your altitude. Generally, jet engines burn less fuel at higher altitudes, with the wind playing a big variable. Obviously, on a long flight, fuel and weight is more critical then a short flight. For example, we were flight planned to fly at 37,000 feet [FL(Flight Level) 370] and land at destination with 6000 (6.0) pounds of fuel. However, as the flight progressed strong turbulence was reported and encountered at our altitude and higher. For safety reasons and a smoother ride we might descend to 31,000 feet (FL 310). Now that we are flying at an altitude 6,000 feet below our projected altitude (especially for a length of time), we will be burning more fuel and thus decreasing the amount of fuel over destination. In essence, you must be very careful that, especially on a long flight, that you are not boxed in a corner. If your preflighted fuel over destination was not much above the recommended minimum fuel for that aircraft to begin with, and predicated on a high altitude for fuel burn, then it could start to get worrisome! All aircraft have recommended minimum landing fuel weights. These are a compilation of weights from the aircraft manufacturer and that airline's policy. Also, while most all Captains follow these guidelines, they might have more conservative weight from their experiences on the aircraft and arriving at your destination.
4) takeoff and landing weights - predicted weights must be within aircraft limitations. For takeoff, the aircraft's structural takeoff weight limitation or runway in use maximum weight cannot be exceeded (more on this in a later section!). For landing, the same parameters apply.
Finally, the Captain signs the Dispatch Release (electronically or written). This means he agrees with the filed flight plan and signs and accepts responsibility for the flight.