If ATC provides a clearance to cross MARRC intersection at FL180, do you still have to maintain that altitude after receiving a new clearance?

In aviation operations, the principle followed is that the most recent clearance from Air Traffic Control (ATC) takes precedence over any previous instructions or clearances. Once a pilot receives a new clearance, it essentially updates the operational parameters, including altitude assignments.

In this context, if ATC grants clearance to cross the MARRC intersection at FL180 and subsequently provides a new clearance, the pilot is obligated to follow the latest instruction. This approach ensures clarity and safety in flight operations, allowing for effective traffic management and reducing the risk of miscommunication.

The understanding that newer clearances supersede previous ones is vital for maintaining safe distances between aircraft and ensuring compliance with ATC directives. Thus, the latest clearance indeed has precedence, leading to an obligation for pilots to adhere to the new altitude instructions provided by ATC.