How the calculator works

What this calculator does

Set the clearance and the heading you are tracking to the fix. It gives you the ICAO entry: direct, parallel or offset, the one American charts call the teardrop. It draws the pattern and the entry sectors around the fix too, so you can see where the answer comes from.

Switch the wind on and it also solves the drift correction, the tripled correction for the outbound leg and the outbound timing, and draws the shape the hold really makes over the ground.

Reading the answer

The entry depends on one angle: the bearing you are arriving from, measured around the fix from the inbound course. The circle splits into three, and the aeroplane on the picture sits in whichever slice you are coming from. Drag it around and watch the answer change as it crosses each boundary. That is the fastest way to get a feel for where the sectors actually sit, and it is why the picture is a control and not a diagram.

The holding is a control too. Take hold of the pattern anywhere on it and turn it round the fix, and the inbound course turns with it, so a clearance can be set up by pointing at it rather than by typing a number. It turns by however far your hand turns, so it never jumps, and the Inbound course field above follows along as you go.

Press SHOW PATH beside the answer and the entry itself is drawn over the pattern: where you would go from where you are, in over the fix, and through the manoeuvre, in the colour of the sector you are in. It is off until you ask for it, so the picture answers the question first and shows you the method second.

The boundaries are the ICAO Doc 8168 ones, 70 degrees on the non holding side and 110 on the holding side, mirrored for a left hand pattern. Nothing here is rounded off or approximated: the same function decides the entry on this page and in the trainer, so the two can never tell you different things.

What the wind does

A hold flown in wind does not trace a racetrack over the ground. It traces what pilots call the potato: one turn blown wide open, the other squeezed shut, and the two legs no longer parallel. Turn the wind on and the picture draws that shape over the still-air one, because the difference between them is the part worth seeing.

The outbound leg is flown at three times the inbound drift correction, not double. You drift for three of the four stretches of a lap, the turn out, the outbound leg and the turn back, and only the outbound leg carries any correction, so it has to work three times as hard. The inbound leg does not count, you are tracking it.