What do flight level changes refer to during an aircraft's journey?

Flight level changes refer specifically to adjustments made to the altitude of an aircraft during its journey. In aviation, altitude is measured in terms of pressure altitude, which is referenced as flight levels (FL). When an aircraft ascends or descends, pilots communicate their altitude intentions using these flight levels, such as FL350 for 35,000 feet.

This concept is essential for maintaining safe vertical separation between aircraft, particularly within controlled airspace. Changes in altitude can occur due to various operational needs, such as avoiding weather disturbances, optimizing fuel efficiency, or complying with air traffic control instructions.

Understanding that flight level changes directly pertain to altitude helps clarify that the other options—relating to speed, weight and balance, or fuel calculations—do not accurately describe this specific aspect of flight operations.