When the dispatcher produces and files the flight plan for a scheduled flight with ATC, are the determined optimal cruise altitudes part of the flight plan, or does the flight plan only contain lateral route information?
The flight plan contains the requested cruise flight level, as well as step climbs or level changes along the route in the route field.
(Image Source: skybrary.aero)
SAM UN621 BASIK/N0412F330 UZ150 BADUR/N0426F340 UN472 ARE/N0424F350 UN864 PIMOS
Fxxx being the requested flight level.
The ATC Flightplan (FPL) does not directly contain the optimum cruise levels for a flight. These levels are calculated and printed in the Operational Flightplan (OFP).
The FPL does contain the requested cruising levels for the flight along its planned route. The requested flight levels (RFL) in the FPL will often be quite close to the optimum cruising levels, but they are unlikely to be exactly the same. This is because there are certain regulatory restrictions regarding which levels can be requested along certain routes. For example, semi circular rules state that flights in specific directions must be flown at a specific range of cruising levels - for example, all westbound flights must fly at "even" flightlevel (FL300, 320, 340, etc.) - the exact rules vary from place to place. There can also be other restrictions in place as a result of active military areas and ATC capacity.
The optimum cruising levels are usually a part of the OFP, and the current optimum level is also shown in the flight management computer in the cockpit. Air traffic controllers do not have direct access to these levels, but pilots will routinely request a level change if their RFL from their FPL deviate significantly from their optimum level.
To recap - the ATC flightplan does contain one or more requested levels for a flight, but these levels are not just based on the optimum performance, they also have to comply with published regulations and restrictions.