Altitudes
An airfield will define a circuit height or pattern altitude, that is, a nominal level above the field at which pilots are required (recommended in the US, FAA AC90-66A Para. 8c )to fly while in the circuit. Unless otherwise specified, the standard recommended pattern height is 1000 ft AGL (above ground level), although a pattern height of 800 feet above ground level is relatively common. Helicopters usually fly their pattern at 500 feet above ground level. Extreme caution is exercised by pilots flying the published traffic pattern altitude as this may contribute to mid air collisions.
Read more about this topic: Airfield Traffic Pattern