When must JAN APCH not transition arriving aircraft beyond the clearance limit?

The correct answer is that JAN APCH must not transition arriving aircraft beyond the clearance limit until the aircraft is at or below 5,000 feet. This is primarily for safety reasons, as maintaining altitude restrictions is critical when managing the flow of aircraft within airspace. Keeping aircraft at or below this altitude helps prevent conflicts with other traffic and allows for safe sequencing of arrivals at the airport.

If an aircraft exceeds the altitude of 5,000 feet before its transition, it may encounter difficulties in safely fitting into the airspace structure, especially in busy terminal areas. This altitude threshold ensures that pilots are managing their descent rates adequately and are able to comply with the instructions given by air traffic control without unnecessary risk.

In the context of the other options, transitioning before reaching the TCP (Terminal Control Point) could allow aircraft to exceed their clearance limit unintentionally, which isn't safe. Confirmation from ZAE before making transitions is usually about ensuring coordination, and waiting to enter the airspace before executing a transition can lead to poor traffic management. Thus, maintaining the proper altitude is essential for orderly and safe operations.