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Holding Pattern (Merriam-Webster) - the usually oval course flown by aircraft awaiting further clearance; especially to land
Hold Procedure (FAA Pilot/Controller Glossary) -a predetermined maneuver which keeps aircraft within a specified airspace while awaiting further clearance from air traffic control
Holding Fix (FAA Pilot/Controller Glossary) - a specified fix identifiable to a pilot by NAVAIDs or visual reference to the ground used as a reference point in establishing and maintaining the position of an aircraft while holding
Holding patterns are flown as a delaying tactic, be it for ATC requirements such as airspace saturation or approach delays, as the published termination of a missed approach procedure to be flown whilst coordinating further clearance, at pilot request to allow time for completion of abnormal or emergency checklist procedures or at any other time that a delay in flight progress is required. Under Instrument Flight Rules (IFR) pilots are expected to adhere to proscribed holding procedures inclusive of speed, hold entry procedures, timing and rate of turn, as the protected airspace for the holding pattern, and thus separation from other traffic, is predicated on those procedures.
Standard Holding Pattern
A standard holding pattern is depicted in the following diagram which shows the ground track as it would appear in still-air conditions. The holding "fix" can be any of a VOR, a NDB, a radial/DME fix, a specified waypoint or, in some circumstances, the current aircraft position as generated by the Flight Management System (FMS).
After the completion of the appropriate procedure to enter the hold, all turns in a standard pattern are to the right. During entry and holding, pilots manually flying the aircraft are expected to make all turns to achieve an average bank angle of at least 25˚ or a rate of turn of 3˚ per second, whichever requires the lesser bank. The inbound leg is flown following the assigned radial or bearing to the fix whilst the ground track for the outbound leg is adjusted for the wind conditions to facilitate the turn to intercept the inbound track. The outbound leg is flown for the appropriate time interval to achieve the regulated inbound timing. Inbound timing for a standard hold is one minute when at or below 14,000' and one and a half minutes when above 14,000'. When the pilot receives ATC clearance specifying the time of departure from the holding fix, adjustments should be made to the flight pattern within the limits of the established holding pattern to leave the fix as close as possible to the time specified.
Non-Standard Holding Pattern
A non-standard holding pattern is one in which the turns are made to the left or the inbound timing is other than standard values. Unless the ATC clearance includes instruction to hold non-standard, make left turns or a non-standard holding pattern is depicted on the chart, pilots are expected to make all turns to the right after initial entry into the holding pattern; that is, a standard holding pattern is to be flown unless specifically cleared otherwise.
Entry sectors for a standard holding pattern are depicted in the following diagram. Note that there are three entry sectors based upon the heading at which the aircraft approaches the holding fix. Note also that there is a zone of flexibility of 5˚ on either side of each boundary; that is, within the zone, the entry procedure appropriate to either side of the boundary can be executed at the discretion of the pilot.
- Sector 1 procedures (parallel entry):
- Upon reaching the fix, turn onto the outbound heading of the holding pattern for the appropriate period of time
- Turn left to intercept the inbound track or to return directly to the fix
- On the second arrival over the fix, turn right and follow the holding pattern
- Sector 2 procedures (offset entry):
- Upon reaching the fix, turn to a heading that results in a track having an angle of 30˚ or less from the inbound track reciprocal on the holding side
- Continue for the appropriate period of time, then turn right to intercept the inbound track and follow the holding pattern
- Sector 3 procedure (direct entry):
- Upon reaching the fix, turn right and follow the holding pattern
Entry procedures to a non-standard holding pattern requiring left turns are oriented in relation to the 70˚ line on the holding side,just as in the standard pattern. Thus the corresponding entry procedure diagram for a non-standard holding pattern is a mirror image of that for the standard pattern.
DME holding is subject to the same entry and holding procedures as a standard holding pattern except that distances, in nautical miles (NM), are used in lieu of time values to define the limits of the holding pattern. In describing the direction from the fix on which to hold and the limits of a DME holding pattern, an ATC clearance will specify the DME distance from the navigation aid at which the inbound and outbound legs are to be terminated. The end of each leg is determined by the DME indications. Conversely, when the aircraft is FMS equipped, a pilot might be cleared to hold at a defined waypoint on a specified track with a specific leg distance expressed in NM.
The expected holding speed for many charted holding patterns is published on the associated enroute, terminal or approach chart. In cases where a speed is not specified, holding patterns must be entered and flown at or below the appropriate airspeed for the holding altitude. These speeds can vary from region to region so pilots must be aware of the limitations in force for the area in which they are operating. International Civil Aviation Organisation (ICAO) maximum holding speeds are as follows:
- Holding altitude 14000' or below - 230 KIAS
- Holding altitude above 14000' to 20000' - 240 KIAS
- Holding altitude above 20000' to 34000' - 265 KIAS
- Holding altitude above 34000' - Mach .83
- Holding patterns restricted to Category A and B aircraft only - 170 KIAS
- Pilots are to advise ATC immediately if airspeeds in excess of those specified above become necessary for any reason, including turbulence. After such higher speed is no longer necessary, the aircraft should be operated at or below the specified airspeeds and ATC notified
- Airspace protection for turbulent air holding is based on a maximum of 280 KIAS or Mach 0.8, whichever is lower, from the Minimum Holding Altitude (MHA) to 34000' and Mach .83 above that altitude.
- Considerable impact on the flow of air traffic may result when aircraft hold at speeds which are higher than those specified above. After departing a holding fix, pilots should resume normal speed subject to other requirements, such as speed limitations in the vicinity of controlled airports, specific ATC requests, etc.
A holding clearance issued by ATC will include at least the following items:
- a clearance to the holding fix
- the direction to hold from the holding fix
- a specified radial, course, or inbound track
- if DME is used, the DME distances at which the fix end and outbound end turns are to be commenced (hold between [number of miles] and [number of miles]). If the outbound DME is not specified by ATC, pilots are expected adhere to the standard holding pattern timing procedures above
- the altitude or FL to be maintained
- the time to expect further clearance or an approach clearance or the time to leave the fix in the event of a communications failure
For example, "BA123 is cleared direct the SHA VOR, descend to and maintain FL180. Hold South East on the 140 degree radial. Expect further clearance at 1035Z". If the holding procedure is charted, the clearance can be abbreviated to exclude the published information. "BA123 cleared to OLLNO, hold as published, maintain FL120. Expect approach clearance at 2215Z".