Holding Management

Holding management is an essential part of providing professional ATC - not only but especially in high traffic situations. This tutorial shows what to keep in mind regarding holdings and includes basics of holdings and advanced holding management.

Definition

A holding (or holding pattern or hold) is a maneuver designated to delay airplanes in flight by keeping them within a specified airspace. Standard holding patterns use right turns, non-standard ones use left turns. Holding patterns may be published on charts (enroute, STARs, approach) or may be given by ATC. Holdings may be anchored on a VOR, VOR/DME, NDB or compass locator, intersection or DME distances.

Standard Holding Pattern

A standard holding pattern consists of:

• The holding fix
• A right 180° turn at standard rate (3 degrees/sec) away from the holding fix
• An outbound leg (standard length: 1 minute below 14000 ft, see below for speed/altitudes)
• A right 180° turn at standard rate towards the holding fix
• An inbound leg (standard length: 1 minute)

However, pilots have to correct wind shifts, and therefore there is hardly any "ideal" standard pattern.

A standard holding pattern

ATC Holding Clearances

A typical ATC holding clearance for a published holding could be:

"AUA123, enter holding at NERDU as published, maintain 9000ft, (220 knots), 1 minute leg, expect further clearance at 1015Z."

Of course, there are times when an ATC - for any reason - can't clear a published holding. Possible holding fixes can be any waypoints, VORs or NDBs, also DME distances or the current position. Anyway, as it is a non-published holding, ATC has to give more information so that pilots know how to fly the holding - for example: "AUA123, proceed direct and hold at NIGSI, FL110, 2 minutes leg, left orbit, expect further clearance at 1310Z."

For longer holdings keep in mind that the pilot has to crosscheck the EFC-time (expect further clearance-time) with available fuel (reserves). Note: the EFC-time is always assigned in the USA (FAA procedures), however in most parts of Europe and also in South America ATC never gives EFC-time, especially for shorter holdings (10-20 minutes). However, advising an EFC-time - if possible - is always a service for the pilot and should be done.

ATC has to issue further instructions while the airplane is in the hold if:

• The delay exceeds one hour
• A revised EFC is necessary
• Weather is becoming less than the required for the intended approach
• Other operational information is necessary (eg: airport closed)

Altitudes And Speed Restrictions

ICAO holding restrictions

Altitude segment for holding	Speed (IAS/Mach) in the holding	Time length of legs
surface to 14,000 ft	max. 230 kts	1 minute
14,001 to 20,000 ft	max. 240 kts	1 1/2 minutes
20,001 to 34,000 ft	max. 265 kts	1 1/2 minutes
above 34,001 ft	max. 0,83 Mach	1 1/2 minutes

Every published holding has got a minimum holding altitude (MHA) which is noted on the charts. For example, NERDU has an MHA of 5,000 ft (see STAR chart for LOWW here: [1]).

Note that, for operational requirements (e.g. if an extended period of holding is foreseen, to avoid too many “rounds” for passenger comfort or to stay in clean configuration), the pilot may request and ATC grant (if possible), either longer legs (usually 2 minutes) or higher speeds in the holding pattern.

Holding Stack And Separation

In periods of very high traffic it may be required that two or more aircraft hold above the same fix. In this case ATC must consider:

• Approach sequence shall be kept unchanged. The aircraft that enters the holding at first, should leave it at first too.
• Aircraft must be separated 1000 feet vertically.
• Aircrafts may be advised to descend in the holding if necessary for succeeding approach.

An aircraft may be cleared to a level previously occupied by another aircraft only after the latter has reported vacating it, except when:

• severe turbulence is known to exist;
• the higher aircraft is effecting a cruise climb; or
• the difference in aircraft performance is such that less than the applicable separation minimum may result; in which case such clearance shall be withheld until the aircraft vacating the level has reported at or passing another level separated by the required minimum.

When the aircraft concerned are established in the same holding pattern, consideration shall be given to aircraft descending at markedly different rates and, if necessary, additional measures such as specifying a maximum descent rate for the higher aircraft and a minimum descent rate for the lower aircraft, should be applied to ensure that the required separation is maintained.

Radar separation shall not be applied between aircraft holding over the same holding point!

References

United Virtual Airlines Trainings Departement: Pilot's Guide. Holdings (http://www.united-virtual.com/files/documents/UVA_Guides_HOLDING.pdf)