Aircraft categories define the performance envelope and crowd separation requirements for each act. Category I covers high-performance aerobatic aircraft — the most restrictive separation requirements because the risk profile is highest. Category II covers mid-performance aerobatics, formation teams, and warbirds performing aerobatics. Category III is fly-bys and non-aerobatic passes — lowest separation requirements.
And the key constraint for a Basic Air Show?
Cat I aerobatics are not permitted at a Basic Air Show. A Cat I aircraft can perform a limited, non-aerobatic fly-by, but the aerobatic sequence requires an SAB or higher. That’s outside BAB authority. If a performer shows up expecting to fly their full aerobatic Cat I routine at your Basic Air Show, the answer is no.
How does the crowd line connect to aircraft category?
The crowd line placement determines what acts you can authorize. Minimum separation distances are specified in the CoW and FAA Order 8900.1. Physical markers must be placed on the ground and verified against CoW specifications before the show opens. You cannot move the crowd line without a CoW amendment — so if the placement is wrong, you solve it before aerials begin, not by pushing the line a few feet and hoping.
Emergency vehicle access also factors in.
Critical detail. Emergency vehicle routes must remain clear. Crowd line markers and spectator positioning cannot block ARFF or EMS access to the flight line. That gets coordinated in advance with the Airport Manager and emergency services, and it gets confirmed on show day before you open the gates.