In what scenario can arriving aircraft be told they can’t enter class B, C, D, or E airspace?

In situations where visibility is less than 1 mile and the aircraft is not facing an emergency, it is crucial to maintain safe operations within controlled airspace. Class B, C, D, or E airspace has specific visibility and cloud clearance requirements that must be met for an aircraft to safely enter and operate within that airspace. When visibility is below this threshold, the potential for conflict with other aircraft and the risks associated with low visibility operations increase. Therefore, air traffic control may advise arriving aircraft that they cannot enter these classes of airspace to ensure safety by preventing operations that could lead to unsafe conditions.

The other scenarios do not provide sufficient justification for denying entry into controlled airspace. Approaching the runway does not inherently affect the ability to enter these airspace classifications if the pilot meets the necessary visibility and operational requirements. Being within 5 miles of the airport does not automatically restrict entry, as many aircraft operate within that range with appropriate clearances. Lastly, even in emergency situations, pilots often have the authority to enter controlled airspace to ensure safety, making it counterproductive to deny access during such critical moments. Thus, low visibility conditions stand out as a scenario where entry cannot be granted, ensuring air traffic safety protocols are upheld.