quick drift calculation on approach

[skyhigher]

Can anyone explain to me how to use the 1 in 60 rule to calculate the required drift allowance needed on approach?

wind 270/30 kts, runway 33, approach ground speed 140kts?

I used to be know but have a complete memory blank!

thankyou

[qwertyuiop]

Use the "clock code". If the wind is 15 degrees off take 1/4of wind, 30 take 1/2, 45 take 3/4 and 60 and over take all the wind.

On your example the wind is 60 off so take it all, ie 30.

That gives you max drift, divide that by your speed in miles per minute ie about 2 1/2 and you get the drift of 12 degrees.

Very rough but quite easy and close enough.

[hetfield]

WCA = CWC x 60 TAS

So 30kt x 60 / 140 = 13 °

not exactly but good enough

[galaxy flyer]

There is, no doubt, an FMS page that displays wind, drift, air data. Select it before starting approach! The old INS CDUs had a selection for Drift/XTE, marvelous for hand flown approaches. Heading opposite of drift and right on course

GF

[clivewatson]

There is, no doubt, an FMS page that displays wind, drift, air data. Select it before starting approach]

I'm sure there is, but if that's the case why is such geometric wizardry needed?

Oh, silly me - someone might need to pass a European exam, and then graduate to fly a TV screen equipped airplane!

[Intruder]

If you're looking for a "quick" calculation, then turn the airplane into the wind a few degrees. Watch your VOR/LOC needle. Turn again to correct...

[josh121.5]

Another easy method which works pretty well .

*if the difference between ur heading and the wind direction is

90deg - use 1/2 the wind strength and thats ur drift
60deg - use 1/3rd
45deg -use 1/4th
30deg - use 1/5th

so in ur case the drift is approx 10deg !!

[strikemaster82]

I use qwerty's method. I've never heard of "ur drift" though.

[josh121.5]

@strikemaster : how do u use the qwerty method ??

[Checkboard]

josh121.5 Think of a clock face. 15 minutes is ¼ of the way around the face, so this reminds you to use ¼ of the wind speed as the drift angle when the wind is 15º off the nose.

30 minutes is ½ of the way around the face, so this reminds you to use ½ of the wind speed as the drift angle when the wind speed is 30º off the nose ... and so on.


One in 60 method. Take the ground speed and divide it by 60 to get your factor. Divide the crosswind by that factor to get your drift.

[Microburst2002]

Crosswind is

1/2 of wind when at 30º
2/3 of wind when at 45º
90% of wind when at 60º

The required drift for a given crosswind is approximately half of the wind component. (that would be exact for a 120 Kt TAS)

Typical approach TAS is about 140 kt, so it is quite approximate and easy

[Sciolistes]

The clock method is excellent and is easily good enough to dead reckon by. But for approach I prefer to think of drift simply in terms for none, small, medium or lots - 0, 5, 10, 15+ respectively. The wind on approach is constantly changing, I find I just need to point the nose in the right direction by roughly the right amount and then make whatever small adjustments I need to from there.

The same for holds except err on the larger, use the gate to widen the turn if need be.

[Slasher]

....to calculate the required drift allowance needed on approach?

Crab Angle = crosswind component / TAS nm per min.

270* / 330* = 60* off = .9 x 30 = 27kt

140kt = 2.5nm /min

27 / 2.5 (mentally) = 10* crab near enough.

Easy. No wizzwheel or calculator needed.

[whitelabel]

I multiply winspeed X 60. Then devide that figure by TAS and you have max drift!

TAS 120
Wind 180/20
RWY 21

20*60 = 1200
1200/120 = 10 degrees max drift

Wind is 30 degrees off rwy so 1/2 of the max drift is the correction angle (5 degrees)

regards.