FAA experimental aircraft are restricted in operation, including no overflights of populated areas, in busy airspace or with unessential passengers.

North Atlantic airspace is the busiest oceanic airspace in the world with about 1,300 flights a day, most of which are large commercial carriers.

Kyu let Rachel go only when the busy airspace inside the garden was cleared.

Was our Defense Department experimenting with exotic vehicles in one of the busiest airspaces in the world?

Due to their high capacity and busy airspace, many international airports have air traffic control located on site.

The route assigned by air traffic control took them just south and east of Washington, away from the busy airspace around Dulles and Reagan National.

In busy airspace with a number of competing aircraft, the optimum routes and preferred altitudes may well be oversubscribed.

"This is busy airspace around here."

The object(s) maneuvered slowly within a busy airspace near O'Hare International Airport.

The ash was then carried over Europe into some of the busiest airspace in the world.