A holding pattern is a closed, hippodrome-shaped trajectory which is anchored onto a VOR, or a NDB. A holding pattern is usually used by traffic controllers, at a given point of a IFR airway, to regulate the traffic through having planes waiting at such points. Holding patterns too are used along the vicinity of the airport areas, where controllers used them then to scale the arriving planes. The radar-vectored trajectories however, at the major aiports, usually render obsolete the holding patterns as the air traffic controllers are delaying some planes through headings, instead of a holding pattern. Holding patterns are most of the time published on the IFR routes charts. Several planes may be directed towards a same holding pattern with each plane flying at a different altitude. When the lowest plane is cleared off the pattern, each plane then steps down one level
Starting at the anchor, a holding pattern begins with a right turn which brings to the first leg of the pattern -which gets away from the anchor, with a heading published. Then, after one minute -which is the standard time for the leg of the holding pattern- of flight, one turns right again, which brings the plane on the leg of the pattern which brings back to the anchor and which is too flewn in one minute. The standard holding pattern are right-turned as non-standard ones left-turned. The length of a holding pattern may be too measured in NM when the anchoring radionav aid is a VOR-DME (the usual distance then is of 5NM relative to the DME). The turns, on a holding pattern, are to be turns at a standard rate, with the 180° turns flewn in 1 minute by the GA planes, and 2 mn, for the airliners. The speed is limited too along a holding pattern, with 175 kts the max. for a propeller plane -whatever the altitude of the pattern- 200 kts for turbine plane, up to 6,000ft. 230 kts for a turbine plane between 6,000 et 14,000ft, and 265 kts beyond 14,000 ft. Any shift due to wind has to be compensated along a holding pattern
Should the ATC forecast that, at a clearance limit, or at any point of a airway, it will have to have a plane to wait, the controllers had to warn the pilot that the latter will have to hold on a holding pattern. And that has to be done at least 5 minutes before the ETA at the point! As far as a published holding pattern is concernend, the ATC controllers are waiting that the pilot flew the pattern like described on the chart. The controllers too have to tell the time at which the pilot will be cleared for what comes after. A holding pattern ATC request usually is formulated like '“Beechcraft, one seven five, hold east of VIDEE Intersection as published, expect further clearance at 1634.' When the ATC ask for a non-published holding pattern, they give to the pilot all the necessary data for like the heading or duration of the legs, etc.
As the entry into a holding pattern located along a IFR airway does not pose any problem in term of access, with the entry point along the axis of the flight, some other cases oblige to use some entry techniques, function of on what trajectory relatively to the anchoring point of the pattern, the plane is flying (the area surrounding the anchoring point usually is divided into three zones):
|click on the picture to the procedures of entry into a holding pattern|