The designated altitude at which an aircraft is expected to enter a receiving facility area should be confirmed unless?

The correct answer is that the designated altitude should be confirmed unless it is lower than the assigned altitude. This is important because the assigned altitude represents the minimum altitude that the aircraft should maintain for safe operation and separation from other air traffic. If the receiving facility expects the aircraft to enter at a lower altitude than what has been assigned, it may lead to potential safety risks such as inadequate vertical separation from other aircraft. Hence, in such cases, confirming the designated altitude is not necessary since it does not affect safety or operational procedures.

The other options present scenarios that might typically require a confirmation. For example, military flights may have specific protocols, changing weather conditions can impact expected altitudes for safety, and without a filed flight plan, there might be uncertainty regarding the intended route and altitude. However, these situations do not negate the standard operational procedure concerning altitude confirmation in the case of an aircraft entering a receiving facility area.