The Mystery of Holding Patterns

As aircraft cannot stop dead in the sky like a car can at traffic lights, they have to fly a holding pattern, if the approach to land has to be delayed. This is normal when aircraft approach busy airports at peak times. Air Traffic Controllers will hold aircraft over navigation points until they can safely fit them into a safe landing approach pattern. The hold is like a race track pattern over the navigation fix. The aircraft will turn either left and right 180 degrees  taking a minute to turn and roll out. After rolling out the aircraft will fly for one minute and turn again taking another minute to turn and another minute to fly back to the fix. This therefore takes 4 minutes to get around the hold once.  Charts show whether the hold is left turn or right turns and the heading back to the fix.

ATC May have a minimum stack height at which they can descend aircraft to that are holding.  For example one of the holding stacks for Heathrow is over Biggin Hill Airport VOR  ID BIG. The minimum stack height is FL 80.  This is because the Heathrow departing Aircraft fly underneath the arrivals at 6000ft before they climb to cruise level. Vertically the aircraft are placed in the holding pattern 1000 ft above each other. As the bottom one is sent into the approach the aircraft above all drop down one level and stop the descent. This is repeated over and over  again until the aircraft reaches the bottom of the stack then its their time to leave to land. The holding speed is between 210 and 220 knots for jets. if the hold gets full then a further holding pattern is made further back. In the case of Heathrow the second one is at Bexel. There are four stacks for Heathrow. Two to the north of London two to the south. depending on the direction the aircraft is coming from they follow a standard arrival route to the hold.

The aircraft  turn with 25 degrees bank normally in the  hold.  This is known as a rate one turn when an aircraft can turn 180 degrees in one minute.

Winds can distort the hold you will need to add 1 second for every knot of headwind subtract one knot for every knot of tailwind on the outbound legs..  With a crosswind you may have to treble the drift as the wind will push you out in the turn and the holding pattern.  The pattern will then look more like a triangle then. Remember there maybe aircraft  1000 ft above and below you doing the same in the hold so

Make sure you stay at your assigned altitude in the hold

Before you can fly a hold, you have to work out how to get into the pattern  This means changing direction in some cases, to get the aircraft flying the hold the correct way round. Below shows the methods of doing this. You will see it is governed by the direction you approach the hold from.

Teardrop Entry Direct Entry Opposite Direction

The hold is shown in blue and the approach to join the hold is shown in dotted green  tracks

In teardrop or opposite direction approaches the aircraft is facing the wrong way for the hold so has to turn 180 degrees to get into the hold the correct way round.  The aircraft will fly over the fix and outbound for one minute before turning directly back to the fix shown in red and  then commence the hold. (as shown above ) When over the fix for the second time they turn the correct way around the hold. report holding to ATC on the  radio.