When must ZAE forward the destination airport to JAN APCH?

The appropriate situation for ZAE to forward the destination airport to JAN APCH is when the arrival is not targeting JAN. This is crucial because communication of the destination allows JAN APCH to prepare for potential traffic, manage airspace, and ensure they are aware of any aircraft that may not be routing directly to their control area. Clear information about the destination is necessary for effective traffic management and safety.

The other options do not accurately reflect necessary procedures. Forwarding destination airport information as soon as the aircraft departs is not always practical or necessary, especially in a busy airspace where multiple destinations are in play. Communication for emergency landings may be different and is typically handled on a case-by-case basis rather than being a standard procedure for all flights. Lastly, waiting until the clearance limit is reached does not serve air traffic control's proactive approach in managing air traffic flow effectively, hence why the correct answer is when the arrival is not targeting JAN.