Starlionblue is right. Most work is done by the Operations department. However we have the final responsibitlity that we meet all the requirements before we enbark on a flight.
On a normal shorthaul flight we check the weather for our departure, arrival and alternate airfields. And offcourse some of the inflight diversion airfields. NOTAMS will be checked and any defects on the aircraft which can have a significant operational impact. With this information in mind we make a decision on how much fuel we take. That's more or less it. On arrival in the aircraft we load the FMGC (Airbus) or FMS (Boeing) and check if our routing is as per filed flightplan.
On a longhaul flight there is a bit more to do. Most steps are as above only now we need to pay more attention to our diversion airfields. Our aircraft (A330) are 180 min ETOPS. So for every diversion airfield you get a 'window' in which you are likely to use this airfield in case of an inflight diversion. In this 'window' the forecast weather has to fullfil several requirements which are more restricting than the weather maybe during an actual diversion. Remember this is all at planning stage. After we both agree that the weather on our selected airfields is above planning minima we then plot the route on a plotting chart. On this plotting chart arcs are drawn to identify the ETOPS sections and our maximum 180 min from a suitable airfield. We both have to check that we have plotted the correct routing on the chart and that the route stays within 180 min of a suitable airfield.
In the mena time the PF
is loading the FMGC and when he is finished we both again have to confirm tracks and distances between waypoints. On atlantic crossing we check the lat and long for every position to be absolutely sure that we have the correct routing in the FMGC.
This can take quite some tie and a standard turn around for our aircraft is 90 min. And we first have to wait till the other crew has left the flight deck. Asyou can see there isa lot to be done in a short space of time. If we have to do everything ourselves we need a much longer turn around time.
Just one thing. On a shorthaul flight we report for duty an hour before the flight. On a longhaul flight we normally report 1:15 hour before the flight. However most of the crew are in the office approx 1:45 hour before a longhaul flight.
Hope this helps.