Wind Correction Angle (WCA)

[gilla]

Can anyone give me a rule of thumb way to remember the wind correction angle in the hold.

I have my IMC renewal coming up and cannot remember the rule of thumb way of working it out. I don't want to have to get my wizz wheel out while in the hold at 2500' waiting to enter the procedure for the ILS.

[Noggin]

Nice and Simple!

max drift = Windspeed at 60 Kts or 1/2 Windspeed at 120 Kts
So for 90 Kts =2/3 Windspeed

0-30 degrees off 1/3 of max drift

30-60 degrees off 2/3 of max drift

60 - 90 degrees off = max drift

[BEagle]

Not quite. Max Drift = Windspeed in Knots/TAS in nm per minute. E.g. - 15 kt of wind, TAS 90 kts, Max Drift = 15/(3/2) = 10 deg.

Angular factor is the same as on your wristwatch. 30 off is 1/2, 15 off is 1/4, 60 or more - use all of max drift.

That's the basic drift sorted. Apply 3 times the assessed drift outbound in the hold (up to a max of 45 deg) and the basic drift inbound.....

But there is NO REQUIREMENT to fly a hold on an IMC revalidation unless ATC so direct.

[DFC]

Two simple methods - one simple brain work and the other visual but slightly less acurate.

Method 1 - "6th sense"

work out the crosswind component as follows;

10 deg off track = 1/6 of wind speed
20 deg off track = 2/6 of wind speed
etc until
60 to 90 deg off = 6/6 of wind speed.

Having calculated the crosswind as per above, divide this by the number of miles per minute True Air Speed you are doing.

60 Kt is 1nm per minute, 120Kt is 2nm per minute etc.

The answer is the WCA.

To find out the headwind/tailwind, use the above method for calculating crosswind but start at the 90deg to track position.

This above method can be used for enroute navigation especially during diversions. It is accurate enough to dispense with the back of the whiz wheel.

Example:
Track 270 TAS 120Kt
Wind 230/24

The angle between the track and the wind is 270-230 =40deg.
The crosswind is 4/6 of 24 = 16Kt

120Kt is 2nm per minute so the WCA is 16/2 = 8 deg.

The wind is 50deg from the abeam (90 deg to track) since 180 deg is abeam and thus 230-180 = 50 deg.

Thus the headwind is 5/6 of 24 = 20Kt.

One can use this headwind to adjust the timing in the hold or enroute to give a ground speed of 100Kt. One can then either say that this is near enough to 1.5nm per minute or to be super accurate, use the whiz wheel or a calculator to work it out exactly.

The visual method is using the DI.

Using a soluble pen draw a vertical and a horizontal line on the DI through the aircraft symbol. Divind this line into 1/10ths eash side of the aircraft. Thus one has 10 divisions above the aircraft and 10 divisions below etc. (This is done before departure).

Going back to my example, place 270 at the top.

The outer edge of the glass represents the max wind speed.
Locate 230 on the edge and drop vertically to your line. You can then read off the 1/10ths of maximum windspeed that is the crosswind. Going back to the 230 position on the edge, move horizontally to obtain the headwind.

With practice, the lines can be dispensed with and also the requirement for the track to be at the top.

With the crosswind, one must once again divide this figure by the number of miles per minute TAS to obtain WCA.

This second method is very useful as a quick crosswind check on final approach.

Hope that I have made it simple enough.

DFC

[RotorHorn]

Very useful.

Have printed off your responses for later contemplation since on first reading my brain exploded... :eek:

glad we don't have IMC for fling wings.... :D

and in most cases we don't have a DI either.... :rolleyes:
hence the big plastic window at the front I suspect...