Flying holds and wind correction
 

Just wondering how you guys work out wind correction on the outbound leg of holds.

After searching the archives the 3 X WCA outbound theory is the most popular (especially in the UK). However, over here it just seems to be a matter of adjusting bank angles and outbound timing (from what I have seen anyway). I have tried both methods and they have their merits.

However:

1. The 3 X WCA method is all very well when you have a VERY good idea of what the wind is doing which is not always possible, especially at the top of the Nth Island.

2. Adjusting bank angles seems to conflict with the idea that we should maintain rate one turns in holds.

I also came upon a post that goes into great depth on how to work out WCA. It involved a great deal of mathematics and head down flying (eyes off the panel). Do pilots really do this?

I use the 3 x WCA method and it seems to work out OK.

As for determining the WCA, I use the following method

1. Determine the amount of drift for full crosswind (ie on a 30knt day in a 180 knot aircraft max drift will be ~10 degrees)

2. mentally overlay the wind direction on the DG and use it like a whiz wheel using +- the drift angle above.

Difficult to describe without a picture.

Bevan..

From the AIP ENR 1.5 - 23
 

3.4 Standard Holding Pattern

3.4.1 When flying the standard holding pattern, an aircraft
must:

a. follow the precribed track inbound to the holding point;
b. execute a 180 degree turn in the direction specified, so as to fly outbound a track parallel to the inbound track;

etc etc

So if you do use the three times drift method you are not complying with the requirements as laid down in the AIP. That said however, I know organisations that teach this method as standard.

I think you'll find that the AIP is no longer a document that sets standards. It's intent, at least under the new CARs, is to explain and clarify specific rules. You don't always need to take the reference to a "180 degree turn" as gospel when drift correction is involved.

This is confirmed by another part of your quote that talks about a TRACK. You use whatever heading is appropriate to maintain that TRACK the best way you can. With correct anticipation of drift after completion of the turn, you may find that you roll out of the turn after something more or less than 180 degrees of turn.

Take the example of a R/H pattern with a +20 degree drift angle set on an inbound course of 360. Heading will be 020. To track outbound on 180, your heading will be 160. Total heading change is 140 degrees.

The same setup with a -20 degree drift angle on the inbound course means a heading of 340. Outbound heading should be 200. Total heading change is 220 degrees.

In each case you will maintain an outbound TRACK that is 180 degrees different from the inbound TRACK. The only real difference is that the outbound track is a DR track.

I think one of us has missed the point.

If the pilot plans to use 3 times the WCA as mentioned above, then the aircraft will not TRACK PARALLEL to the inbound leg. Which is my point. I am very comfortable with the difference between track & heading. However some of the pilots that I flight test seem to have a problem with it.

Agreed that the turn will not always be 180 degrees. It will vary by the amount of drift correction + or -. That was not disputed.

Icarus2001

So from a flight testing standpoint it is OK to vary turns rates in holds as long as a rate one is not exceeded as long as a track parrallel to the inbound is maintained.

Correct??

Not only is it OKAY to vary the AOB to adjust the turn rate(up to rate one or 25), it really is required...

Thanks Icarus

The reason why I started this post is that after reading the archives I noted that the Europeans use WCA x 3 almost exclusively with no variation from rate one of 25 degrees. Seems very strange.

Take a look at AIP ENR 1.5 3.2.1 e.

Yes Icarus, that's a fair point. I had to re-read my previous post to realise that it was missing the final couple of paras. I wrote the whole thing in Notepad, then did a cut and paste but, somehow, I missed the last two paras. Doh!

They were the ones that explained that, while all of the above was the theory, I'd only posted it by way of getting to the point about turning thru more or less than 180 degrees. Then a quick discussion of why the 3-times WCA technique works well and is, in fact, a bit of overkill in a one-minute pattern.

It's not a serious problem in such a short pattern, but I wouldn't use such a drastic drift correction angle in a longer holding pattern, or a racetrack approach procedure, where outbound timing can be up to 3 minutes or more. There's a greater risk of straying outside the primary protection area in such cases.

We are taught to use "double the drift" on the outbound leg, i.e holding ten degrees drift inbound then twenty geress outbound. Worked pretty well for us.

I believe in this philosophy which seems to comply with all the rules and keep things simple at the same time.... THE PROCEDURES ARE TRACKS

As far as I know ALL procedures on a chart are considered TRACKS (unless specified otherwise). Therefore we should be flying TRACKS at ALL times in a hold - simple. So in a hold when you are flying a track (inbound or outbound) apply drift - the same as you have been doing for the last hour or whatever all they way to the aid. When you are turning inbound or outbound remember that these are also TRACKS so..... as the procedure is based on nil wind rate 1 25 deg etc, apply a correction to bank angle to correct for wind so that the aircraft flies the same TRACK as was originally prescribed in the procedure.

And a question for the Jet guys with all the technology. Does their FMS autopilot thingy fly holding patterns on drift or does it multiply by 2 or 3 or whatever??? And what does it do to bank angle to compensate for wind in the in / out bound turns?

Errm, I beg to differ. An omni-directional wind is considered for the design of the pattern, to establish the protection area. If statistical wind data is available it can be used, otherwise Pans Ops require 3h+47, which is to say, 3 times the height in thousands of feet plus 47. So, if the holding is at 6,000 feet, an onmi-directional wind velocity of ((3x6=18)+47) 65 knots!

The reason for a double or triple WCA is that, if you have an adverse wind during the turn to the O/B leg, the aircraft will be blown back toward the holding point (or fix). Thus, there is a need to ensure that there will be enough distance to allow a neat turn back to the I/B leg.

For the most part, the equipment available to the "jet guys" allows an accurate determination of W/V, which can then be appropriately allowed for. It's only the pilots who lack that sort of sophisticated gear who need to use one or other of the above methods.

I think a practicle look at this situation is required. Don't start shooting yet!

Yes,the holding procedures require tracks and 180 degree turns etc. but if you are descending into a holding pattern, initially, depending on the level of equipment,( let's say a sole ADF preparing for an NDB approach -poor bas####s) then the forecast is the only indicator available as to set up for the outbound leg. So you could carefully calculate the drift with your wizz wheel, apply an outbound heading, and you still would'nt know how your outbound track ended up until turning inbound.

So to make life a bit easier, it was suggested when I did my I/R (>20 yrs ago - no GPS) that you would initially apply 2 times drift for a 2 min pattern, or 3 times drift for a 1 min pattern, and use the information gleaned by the inbound turn and tracking to adjust the next patterns outbound leg. The theory being that after that first pattern, you should have the track pretty well summed up.

The FMCs used on the jets use the FMC derived wind to fly the required entry and holding procedures. So the outbound track will be exactly that, a track

I've been told so many different ways, now I use my own system:

14 times the square root of your grandmothers age divided by the amount of grandchildren she has. The grandmother you use is up to you. Works great!! ;)

So does anyone know what a certain testing officer at the top of the North Island (NZ) requires?

Exactly cap10.. SUCK AND SEE

no_HANDLE you should be studying!!

The UK mob just loves that 3 x the WC. Nearly all of their holds are 1 min right hand pattern. They get all keen about timing, AoB, and gates etc.. The other day I had to do a hold for the LPC, I just sort of winged it with an educated guess and applied enough drift to amuse myself. Amazingly it worked. Must admit, that gate method does give a good idea as to how it's going.

Yeh very true THUMP but you need a break sometimes specially when the nerves get the better of ya.:O