"Recreational use of the NAS is covered by FAA Advisory Circular (AC) 91-57 which generally limits operations to below 400 feet above ground level and away from

"Recreational use of the NAS is covered by FAA Advisory Circular (AC) 91-57 which generally limits operations to below 400 feet above ground level and away from airports and air traffic." This is recreational use, and I consistently see people deferring to this "Advisory" circular which specifically states it merely "encourages voluntary compliance"