Under what condition, if any, may pilots fly through a restricted area?

Pilots may fly through a restricted area only with the controlling agency's authorization. Restricted areas are established for the safety of both the aircraft and the areas on the ground or in the water below, often due to military operations, hazardous activities, or other factors that could pose a danger to public safety.

Obtaining authorization ensures that the pilots are aware of any temporary or ongoing activities that necessitate the restricted status, allowing for safe passage through these zones. This regulation is put in place to protect both the pilots and people on the ground, as well as to preserve the integrity of the operations occurring within those restricted areas.

Other conditions mentioned in the options, such as flying above a certain altitude or specific times, do not apply universally; rather, they do not provide an authorization mechanism like direct communication with the controlling agency does. Special flight permits are also not a general solution for restricted area access but are meant for different regulatory circumstances.