Holding (aeronautics)

In aviation, holding (or flying a hold) is a maneuver designed to delay an aircraft already in flight while keeping it within a specified airspace; i.e. "going in circles."

Implementation

A holding pattern for instrument flight rules (IFR) aircraft is usually a racetrack pattern based on a holding fix. This fix can be a radio beacon such as a non-directional beacon (NDB) or VHF omnidirectional range (VOR). The fix is the start of the first turn of the racetrack pattern. Aircraft will fly towards the fix, and once there will enter a predefined racetrack pattern. A standard holding pattern uses right-hand turns and takes approximately 4 minutes to complete (one minute for each 180-degree turn, and two one-minute straight ahead sections). Deviations from this pattern can happen if long delays are expected; longer legs (usually two or three minutes) may be used, or aircraft with distance measuring equipment (DME) may be assigned patterns with legs defined in nautical miles rather than minutes. Additionally, if there is wind, the pilot is expected to adjust the outbound timing so that the inbound leg can be flown in 1 minute, or 1.5 minutes if it is above 14,000 ft.

History

The 1965 framework standardized such matters as holding speeds, turn performance, outbound timing, wind correction and the construction of protected holding airspace. Procedure designers could consequently account systematically for aircraft speed, turn radius, navigation tolerances, wind and pilot reaction time when determining the area requiring obstacle protection.