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Holding Patterns
A holding pattern can be either for En route traffic or for approaching an airfield. They are normally introduced when traffic congestion makes it unsafe for controllers to allow the aircraft to continue directly to their destination. A hold normally takes 4 minutes to fly round once. Heathrow has 4 holding areas where all inbound aircraft will route to initially as shown in approach charts. Basically the aircraft routes to either a VOR NDB or intersection and then makes a 180 degree turn and flies outbound for one minute. The aircraft then commences another 180 turn back to the beacon again and intercepting the inbound radial as published in the charts. The aircraft should turn the 180 degrees in one minute this is known as a rate one turn. It is important to keep the same bank angle on during the turn otherwise what happens is when you come to turn back into the beacon you will either overshoot the inbound radial or undershoot it and then keep zigzagging to try and get back on it. The result is the next hold gets worse and the one after that even worse. Instead of it being a nice race track pattern it looks like the Olympic rings. You must watch your speed and altitude as well especially if you are in an approach hold as there is normally aircraft 1000ft above and below you doing the same circling procedure. The approach controller keeps pulling the bottom aircraft off for approach and dropping the aircraft above down 1000ft until it reaches the bottom of the stack. When at the bottom of the stack it is that aircrafts turn to approach. It is a bit like the old record player with all the records on top dropping down one at a time and playing. For jets the hold speed is normally 220 knots. The bank angle will vary with speed a jet normally banks with 25 degrees maximum. bank angle.
On the above picture you can now see what a holding pattern should look like. I have changed the bank angle slightly during the turns so you can see already the nice race track is now starting to get distorted. In the above case the aircraft came direct to the VOR and turned right into the hold. It is not always as simple as that as you can see below. The aircraft came to the hold from the opposite direction . The aircraft will have to fly direct to the VOR and then fly outbound for one minute on the inbound radial and commence a rate one turn all the way round back to the VOR. Once back at the VOR turn right into the hold. This method is known as a tear drop type entry.
Traffic from the Right would also use this procedure. Traffic from theLeft would route to the VOR then would turn right and do the tear drop the other way round. In this case flying outbound on a heading of 135 for one minute and commencing a right turn to intercept the inbound radial to the VOR and then turn right into the hold. The hold is easy to fly compared to joining it. The hard bit is working out which procedure to adopt to get the aircraft going the right way round.
The finished product with joining the
hold from the opposite direction should look something like this after the tear
drop and once round. (Note the tear drop.) You may have to also allow for
headwind ,tailwind and crosswind by having to treble the drift heading.
In a crosswind the turns will push you further out and in the head and tailwind case you may
fly outbound for 50 seconds and inbound for 1 minute 10 seconds. Whilst doing
this the controller keeps dropping you a 1000ft and leveling you off, and
then dropping you again.( good fun and faster heartbeat assured) especially when in
turbulence inside a cloud.
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