A shuttle procedure is defined as a

A shuttle procedure is defined as a manœuvre involving a descent or climb in a pattern resembling a holding pattern. Shuttles are generally prescribed on instrument procedures located in mountainous areas. In the approach phase, it is normally prescribed where a descent of more than 2 000 feet is required during the initial or intermediate approach segments. It can also be required when flying a missed approach or departure procedure from certain airports. A shuttle procedure shall be executed in the pattern as published unless instructions contained in an ATC clearance direct otherwise. To ensure that the aircraft does not exceed the obstacle clearance protected airspace during a shuttle descent or climb, the aircraft must not exceed 200 KTIAS while in the shuttle descent or climb, nor exceed one minute outbound still air time. Normal aircraft speed may be flown once the aircraft leaves the shuttle pattern