Holding (aviation) - AbsoluteAstronomy.com

Aviation

Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

, holding (or flying a hold) is a maneuver designed to delay an aircraft already in flight while keeping it within a specified airspace.

Implementation

A holding pattern for instrument flight rules

Instrument flight rules

Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual 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

Non-directional beacon

A non-directional beacon is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF...

(NDB) or VHF omnidirectional range

VHF omnidirectional range

VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...

(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

Distance Measuring Equipment

Distance measuring equipment is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals....

(DME) may be assigned patterns with legs defined in nautical mile

Nautical mile

The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...

s rather than minutes. Less frequent turns are more comfortable for passengers and crew. Additionally, left-hand turns may be assigned to some holding patterns if there are airspace restrictions nearby.

In the absence of a radio beacon, the holding fix can be any fixed point in the air, and can be created using two crossing VHF omnidirectional range radials (also called intersection), or it can be at a specific distance from a VOR using a coupled distance measuring equipment. When DME is used, the inbound turn of the racetrack may be permanently defined by distance limits rather than in minutes. Furthermore, in appropriately equipped aircraft, GPS waypoints may be used to define the holding pattern, eliminating the need for ground-based navigational aids entirely.

A hold for visual flight rules

Visual flight rules

Visual flight rules are a set of regulations which allow a pilot to operate an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minimums, as specified in the rules of the...

aircraft is usually a (smaller) racetrack pattern flown over something easily recognizable on the ground, such as a bridge, highway intersection or lake.

Usage

The primary use of a holding pattern is delaying aircraft that have arrived at their destination but cannot land yet because of traffic congestion, poor weather, or runway unavailability (for instance, during snow removal

Snow removal

Snow removal is the job of removing snow after a snowfall to make travel easier and safer. This is done by both individual households and by governments and institutions.-De-icing and anti-icing:...

). Several aircraft may fly the same holding pattern at the same time, separated vertically by 1,000 feet or more. This is generally described as a stack or holding stack. As a rule, new arrivals will be added at the top. The aircraft at the bottom of the stack will be taken out and allowed to make an approach first, after which all aircraft in the stack move down one level, and so on. Air traffic control

Air traffic control

Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

(ATC) will control the whole process, in some cases using a dedicated controller (called a stack controller) for each individual pattern.

One airport may have several holding patterns; depending on where aircraft arrive from or which runway is in use, or because of vertical airspace limitations.

Since an aircraft with an emergency has priority over all other air traffic, they will always be allowed to bypass the holding pattern and go directly to the airport (if possible). Obviously, this causes more delays for other aircraft already in the stack.

Limiting usage of holdings

Aircraft flying in circles is an inefficient (and hence costly) usage of time and fuel, so measures are taken to limit the amount of holding necessary. Air traffic flow management

Air traffic flow management

Air Traffic Flow Management is the regulation of air traffic in order to avoid exceeding airport or air traffic control capacity in handling traffic, and to ensure that available capacity is used efficiently....

is used to delay aircraft while grounded at their departure points when delays are expected at their destinations.

Flying a holding pattern

Many aircraft have a specific holding speed published by the manufacturer; this is a lower speed at which the aircraft uses less fuel per hour than normal cruise speeds. A typical holding speed for transport category aircraft is 210 to 265 knots (519.4 km/h). Holding speeds are a function of aircraft weight at the point of holding. If possible, a holding pattern is flown with flaps

Flap (aircraft)

Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...

and landing gear

Undercarriage

The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...

up to save fuel.

Entry procedures and accurate flying of the holding procedure are essential parts of IFR pilot

Aviator

An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

training

Training

The term training refers to the acquisition of knowledge, skills, and competencies as a result of the teaching of vocational or practical skills and knowledge that relate to specific useful competencies. It forms the core of apprenticeships and provides the backbone of content at institutes of...

, and will always be tested on examination flights.

Modern autopilot

Autopilot

An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles...

s, coupled with flight management system

Flight management system

A flight management system is a fundamental part of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern aircraft no longer carry flight engineers or navigators. A...

s, can enter and fly holding patterns automatically.

Entry procedures

The entry to a holding pattern is often the hardest part for a novice pilot to grasp, and determining and executing the proper entry while simultaneously controlling the aircraft, navigating and communicating with ATC requires practice. There are three standard types of entries: direct, parallel, and offset (teardrop). The proper entry procedure is determined by the angle difference between the direction the aircraft flies to arrive at the beacon and the direction of the inbound leg of the holding pattern.

A direct entry is performed exactly as it sounds: the aircraft flies directly to the holding fix, and immediately begins the first turn outbound.
In a parallel entry, the aircraft flies to the holding fix, parallels the inbound course for one minute outbound, and then turns back, flies directly to the fix, and continues in the hold from there.
In an offset or teardrop entry, the aircraft flies to the holding fix, turns into the protected area, flies for one minute, and then turns back inbound, proceeds to the fix and continues from there.

The parallel and teardrop entry are mirrored in case of a left-hand holding pattern.

Speed limits

Maximum holding speeds are established in order to keep aircraft within the protected holding area during their one-minute inbound and outbound legs. For civil aircraft

Civil aviation

Civil aviation is one of two major categories of flying, representing all non-military aviation, both private and commercial. Most of the countries in the world are members of the International Civil Aviation Organization and work together to establish common standards and recommended practices...

(not military

Military aviation

Military aviation is the use of aircraft and other flying machines for the purposes of conducting or enabling warfare, including national airlift capacity to provide logistical supply to forces stationed in a theater or along a front. Air power includes the national means of conducting such...

) in the United States, these airspeeds are:

Up to 6,000 ft MSL: 200 KIAS
From 6,001 to 14,000 ft MSL: 230 KIAS
14,001 ft MSL and above: 265 KIAS

The ICAO Maximum holding speeds:

Up to 14000 ft: 230kts
14000 ft to 20000 ft: 240kts
20000 ft to 34000 ft: 265kts
Above 34000 ft: M0.83

With their higher performance characteristics, military aircraft have higher holding speed limits.

In Canada the speeds are:

All propeller including turboprop aircraft - MHA^† to 30000 ft (9,144 m): 175 knots
Civilian Jet - MHA to 14000 ft (4,267.2 m): 230 knots
Above 14000 ft: 265 knots

Climbing during the hold:

turboprop - normal climb speed
Jet aircraft - 310 knots maximum

^†MHA – Minimum Holding Altitude

Timing corrections

In order to achieve a one-minute inbound leg, there are two key ways to modify timings:

Simple Method: If inbound leg is less than one minute, add the same number of seconds to the outbound leg. If the inbound time is more than one minute, subtract the same number of seconds from the outbound leg.
- i.e. Inbound time is 0:55 --> Outbound time is 1:05
- i.e. Inbound time is 1:06 --> Outbound time is 0:54
Ideal Method: Subtract 2/3 of the error (in seconds) for inbound legs more than one minute, and add 3/2 of the error (in seconds) for inbound legs of less than one minute.
- i.e. Inbound time is 0:55 --> Error is 5 seconds. Thus +3/2*5=+7. 1:00+0:07=1:07. Fly 1:07 Outbound.
- i.e. Inbound time is 1:06 --> Error is 6 seconds. Thus (-2)/3*6=(-4). 1:00-0:04=0:56. Fly 0:56 Outbound.
For an initial gauge, add the headwind or subtract the tailwind component speed in knots.
- i.e. Initial outbound with a tailwind component of 7 knots. Initial outbound 0:53.
- i.e. Initial outbound with a headwind component of 20 knots. Initial outbound 1:20.

External links

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