The purpose of a holding pattern is to provide a delay, or time buffer, to an aircraft in flight, whilst also keeping it within designated airspace. This serves a variety purposes, for example, to mitigate airspace saturation, delays to approach and for providing time for pilots to complete abnormal or emergency procedures. The Fix is a geographic reference point from which the hold is flown, relatively - a Fix can be a radial beacon, such as a VOR or NDB, a radial/DME Fix, or a designated waypoint.
Standard and Non-standard Holds
Standard Holds are flown in a Right-handed pattern, from the Fix. On completion of the Holding Pattern Entry to enter the Hold (see below), all turns in the Standard Hold are flown in a Right-handed pattern. All turns in the Hold must be, on average, standard rate (3°/sec) or at least 25° bank angle, whichever requires lesser bank angle.
The timing of the legs of a Standard Hold are:
- Up to FL140 - one minute
- Above FL140 - one and a half minutes
Non-standard Holds are explicitly instructed by ATC, so unless instructed, all Holds are Right-handed. Left-handed Holds are mirror images of their Standard (Right-handed) Holds.
There are three different Hold Entry Patterns used to enter a Hold, the pattern of which varies depending on the Heading in relation to the Hold direction. The above diagram depicts these three different types of entry, namely Direct, Parallel and Teardrop.
There is a tolerance of +/- 5° at each sector boundary, which means that within this tolerance, the chosen Pattern Entry is at the pilot's discretion.
We also need to correct for the Wind Vector (direction and speed), hence the WCA (Wind Correction Angles) required are applied to the Headings to fly, as indicated on the Top-Right of the visualisation.
- Direct - Fly to the Fix. Then, fly the Holding Pattern.
- Parallel - Fly to the Fix. Cross the Fix, then, if necessary, fly a turn in the opposite direction to the Holding Pattern to align with flying the INBOUND leg in the opposite direction. After this leg has been flown, turn again (in the opposite direction to the Hold) and fly to the Fix. Once at the Fix, fly the Holding Pattern.
Teardrop - Fly to the Fix. Cross the Fix, then fly 30 degrees offset from the OUTBOUND course for 1 minute. Then, turn in the direction of the HOLD to intercept the INBOUND. Finally, once at the Fix, fly the Holding Pattern.
Holding Pattern Speed Restrictions (ICAO)
ICAO (International Civil Aviation Organisation) have established the following Speed Restrictions for Holding Patterns:
- Up to FL140 - 230 kn
- FL140 to FL200 - 265 kn
- Above FL200 - M0.83 (mach 0.83)