What is required to let an IFR aircraft descend through another airspace?

For an IFR (Instrument Flight Rules) aircraft to descend through another airspace, a point out is required. A point out is a communication process in which one air traffic controller informs another controller of an aircraft's intention to operate within the latter's airspace. This allows for the coordination necessary to ensure that the traffic is managed safely and efficiently.

When a controller makes a point out, it establishes everyone's situational awareness regarding the aircraft's trajectory and intentions, thus facilitating the safe descent of the IFR aircraft through the adjacent airspace. This communication is typically verbal and requires acknowledgment from the receiving controller, which helps maintain clear communication and proper separation between aircraft.

While other methods of communication, such as verbal clearances or handoffs, are essential in air traffic management, a point out is specifically utilized for the purpose of coordinating the passage of an aircraft through another controller's airspace without a formal clearance or handoff.