Upon approval to change altitude from FL250 to FL310, what report is required?

When transitioning from one altitude to another, pilots are required to provide specific reports to air traffic control, which helps maintain situational awareness and ensures safe separation between aircraft. The correct report in this scenario is to indicate that the aircraft is leaving the current flight level of FL250 while climbing to the new assigned level of FL310.

This report is critical because it informs air traffic control that the aircraft is actively changing altitudes. It not only confirms the pilot's acknowledgment of the altitude clearance but also serves as a notification that the aircraft is in the process of transitioning to a new flight level. Reporting while climbing and indicating the specific altitude being vacated allows controllers to monitor aircraft movements effectively and manage airspace efficiently.

Other reporting options do not provide the necessary context or information that controllers need to maintain safety. For example, simply reporting climbing to FL310 does not confirm when the aircraft leaves FL250. Meanwhile, reporting "at FL310 now" indicates a completed climb without giving a status update on the previous altitude, which could lead to gaps in communication. Similarly, stating "current altitude FL250" fails to communicate the intention to change altitude and could mislead controllers regarding the aircraft's intentions.