What is the function of a fix in relation to altitude changes?

A fix serves as a crucial reference point in an IFR flight for initiating altitude changes. When a pilot approaches a predetermined fix, it often corresponds with specific altitude instructions that are part of air traffic control (ATC) procedures. For instance, pilots may be instructed to climb or descend to a certain altitude upon reaching a fix, facilitating controlled and safe altitude changes in conjunction with flight path management. This allows pilots to adhere to ATC clearances and ensures separation from other aircraft, making fixes a vital component of altitude management during flight operations.

While fixes can be used for navigation, turning maneuvers, and indirectly maintaining speed, their primary purpose in the context of altitude changes is to provide reference points for vertical navigation as specified in flight procedures.