Holding patterns is the pattern, or manoeuvres, that an aircraft takes before landing. However, the question still remains, why are holding patterns important? Why can’t the plane just land? Why do they have to enter holding patterns? Often times, you can see aircrafts circling radio beacons, this is because they are not able to land yet and are currently in holding, usually in an oval pattern.
There are a number of reasons that would cause the pilot to enter a holding pattern. Holding patterns are used to prevent accidents from occurring. In some cases, incoming aircraft may be stacked due to ground (on the runway or the taxi way) or air traffic, poor weather, or runway unavailability. Another reason to enter a holding pattern may be due to a request from the pilot to allow time to handle any emergencies on board or for any other reasons that requires a flight delay as holding patterns serves as a delaying tactic.
On the ground, aircrafts are able to stay in ‘waiting rooms’. Holding stacks are waiting rooms for aircrafts before landing. London Heathrow Airport has got 4 holding stacks; Bovingdon, Lambourne, Ockham and Biggin. Due to Instrument Flight Rules (IFR), pilots have got certain rules and procedures to abide to during holding, including speed limits, hold entry procedures, timing, and the rate of turn. This allows for the Air Traffic Controller (ATC) to be able to arrange the separation of the aircraft with another aircraft.
There are two phrases to keep in mind when talking about holding patterns; Holding procedure and Holding fix. A holding procedure, as defined by the FAA, is a predetermined pattern that keeps the aircrafts within a specified airspace while awaiting further clearance from the Air Traffic Controller (ATC), while a Holding fix is a specified fix that can be identified by a pilot, often through NAVAIDs or visual references to the ground. The ground in this case is used as a reference point when establishing and maintaining the position of an aircraft during holding. Incoming aircraft may be stacked due to traffic, poor weather or runway unavailability.
Now, let’s talk about the procedures pilots must follow in order to enter holding patterns. Most pilots undergo the standard procedure, but sometimes pilots will be ordered to undergo the non-standard procedure. Standard conditions are only true when ground track is in still-air conditions. Holding fix can be of VHF Omnidirectional Radio Range (VOR), an NDB, a radial/DME fix, a specified Waypoint or due to the Flight Management System (FMS). VOR is an aircraft navigation system operating in the VHF band and may be combined with data from the aircraft to provide bearings that corresponds to the aircraft’s axis. NDB, or the Non-Directional Beacon, is a radio beacon that operates in the MF or LF band-widths in order to transmit a signal of equal strengths in all directions.
After completion of all procedures required to enter hold, the standard pattern shows that all aircrafts must turn to the right. During entry and holding, pilots must achieve an average bank angle of 25 degrees or so. The inbound leg is flown following the bearing to the holding fix while the ground track for the outbound leg will be adjusted to the current wind conditions in order to adapt to the intercepting turn on the inbound track. The outbound leg is then flown for just the right amount of time in order to achieve the right inbound timing of around 1 minute when below 14000 ft and 1 1/2 minutes when above 14000 ft. When the Air Traffic Controller (ATC) gives clearance to the pilot, adaptations can be made to the flight patterns that must be within the limits of the holding pattern in order for the aircraft to be able to escape the pattern as soon as the holding ends. A non-standard holding pattern only occurs when the aircraft is made to turn to the left, as opposed to standard holding patterns that turns to the right. Non-standard holding patterns only exists when the pilot is told to do so by the ATC. Otherwise, pilots must follow the standard holding pattern that would have the plane turning to the right after initial entry into the holding pattern.
So, why are holding patterns important? In conclusion, without holding patterns, air traffic would be chaotic and aircrafts would crash into one another. With holding patterns, this gives way for each aircraft to land safely and prevent any incidents from happening. Holding patterns would also allow pilots to land safely during bad weather scenarios or if there are emergencies on board. Basically, holding patterns are crucial to the aviation world and it is required for all pilots to have an understanding of holding patterns, both basic and advanced. Join 14DAYPILOT Flight Academy to learn on how to become a pilot and we will help you become one.