What is an "operational" clearance?
Wondering if anyone can explain what it means to get an "operational" clearance. Context: I was recently flying in Niger, and frequently heard various military aircraft and military/government contracted aircraft request and receive (prior to takeoff) a clearance to be "Operational on XXX Radial". It generally seemed to be requested by aircraft whcih were not flying to another destination, ie: were departing on an airborne mission with the intent of landing back at the airport of departure following mission completion. The aircraft requesting such were not local ie: not Niger Armed forces, but aircraft from other countries operating within the country. Any idea what this means? I heard a suggestion that it was the same as operating "Due Regard". I'm familiar with the concept of operating with "Due Regard" but in other places where I have heard military or State aircraft operating "due regard" the phrase "due regard" was used to invoke that. Is this an Niger or Africa thing? Is it a NATO/US military term? I'd appreciate any light whcih could be shed on this. Supporting references would be appreciated even more. Thanks.