Crosswind Components

drunkenbeagle

drunkenbeagle

Gang Member
Okay, had this as a question for an A/C checkout recently:

ASOS reports winds 320@30. Demonstrated Crosswind Component 15kts. Landing RWY 29, will the demonstrated crosswind be exceeded?

I said not enough information to answer the question.

Comments? Am I being silly? The point of the question was probably to show if you know how to use a whiz wheel. (I do the math in my head).

Discuss.
 
drunkenbeagle said:
Okay, had this as a question for an A/C checkout recently:

ASOS reports winds 320@30. Demonstrated Crosswind Component 15kts. Landing RWY 29, will the demonstrated crosswind be exceeded?

I said not enough information to answer the question.

Comments? Am I being silly? The point of the question was probably to show if you know how to use a whiz wheel. (I do the math in my head).

Discuss.
Click to expand...

Ever see a headwind/xwind component chart before?

windcomponent.jpg
 
drunkenbeagle said:
Okay, had this as a question for an A/C checkout recently:

ASOS reports winds 320@30. Demonstrated Crosswind Component 15kts. Landing RWY 29, will the demonstrated crosswind be exceeded?

I said not enough information to answer the question.

Comments? Am I being silly? The point of the question was probably to show if you know how to use a whiz wheel. (I do the math in my head).

Discuss.
Click to expand...
Okay it is a 30 angle off your wing assuming runway 29 is exactly 290 degrees. So you have a xwind of 30 degrees. the sin of 30 degrees is .5 .
.5 x 30 is 15 knts. so no... now if runway 29 is 289 degrees then you exceed it.
 
drunkenbeagle said:
Okay, had this as a question for an A/C checkout recently:

ASOS reports winds 320@30. Demonstrated Crosswind Component 15kts. Landing RWY 29, will the demonstrated crosswind be exceeded?

I said not enough information to answer the question.

Comments? Am I being silly? The point of the question was probably to show if you know how to use a whiz wheel. (I do the math in my head).

Discuss.
Click to expand...

How is there not enough information?

You can easily get the actual runway heading + you know the reported winds + crosswind component chart = plenty of information to answer the question.
 
ctab5060X said:
How is there not enough information?

You can easily get the actual runway heading + you know the reported winds + crosswind component chart = plenty of information to answer the question.
Click to expand...

yup, technically you don't need a crosswind component chart.
 
Did you steal that chart out of my C-5 performance manual? HA! You want a chart? Try this one out....
 

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Remember that demonstrated crosswind is not a restriction or a limitation. Crosswind limitations should be on the pilots ability only.

Computing crosswind components is something you'll appreciate if you can do the mental math. I highly recommend finding a method you like, and learning it.
 
nosehair said:
Probably :crazy:
Click to expand...

The point is that winds are generally reported True, and Runways are magnetic. ASOS reports true winds (per the FAA). With a 20 degree magnetic variation, what you thought was a 10 kt crosswind might actually be closer to 30 kts. Plus the runway heading might be different, as pointed out.

If you take a look at some airports in the Northeast, you can easily construct a scenario where ignoring variation and rwy headings gives you a 10kt crosswind, while taking them into account might give you a 30kt crosswind.

My concern is that you can't answer such questions without knowing what airport. It seems to me you should be using the correct numbers in the first place (i.e. the actual airport numbers from the AF/D)
 
drunkenbeagle said:
The point is that winds are generally reported True, and Runways are magnetic. ASOS reports true winds (per the FAA). With a 20 degree magnetic variation, what you thought was a 10 kt crosswind might actually be closer to 30 kts. Plus the runway heading might be different, as pointed out.

If you take a look at some airports in the Northeast, you can easily construct a scenario where ignoring variation and rwy headings gives you a 10kt crosswind, while taking them into account might give you a 30kt crosswind.

My concern is that you can't answer such questions without knowing what airport. It seems to me you should be using the correct numbers in the first place (i.e. the actual airport numbers from the AF/D)
Click to expand...

I thought winds aloft were true and surface winds mag. I didnt know that.
 
drunkenbeagle said:
The point is that winds are generally reported True, and Runways are magnetic. ASOS reports true winds (per the FAA). With a 20 degree magnetic variation, what you thought was a 10 kt crosswind might actually be closer to 30 kts. Plus the runway heading might be different, as pointed out.
Click to expand...

This is not correct amigo. ASOS provides mag wind. I was 99.99 percent sure, but I went and checked.

http://www.nws.noaa.gov/asos/magwind.htm
 
ctab5060X said:
I was thinking it was incorrect as well.

Thanks for the clarification!
Click to expand...

But interesting enough it says that asos derived winds for metar and speci reports are in true. So if you hear asos over the radio it is mag... I could see where his confusion was.
 
ctab5060X said:
I saw that as well.
Click to expand...

Hold on, I just looked it up yesterday. All FAA freqs transmitting winds are supposed magnetic, unless noted otherwise. Though I was reading NOAAs documentation for ASOS which said it reports true.

EDIT: Just looked it up again. ASOS reports both magnetic and true winds. True winds are reported on METARS/FSS/NWS, magnetic by telephone and ground to air.

From the ASOS book:
WIND DIRECTION AND SPEED: Direction in tens of degrees from true north (first three digits);
next two digits: speed in whole knots; as needed Gusts (character) followed by maximum observed
speed; always followed by KT to indicate knots; 00000KT for calm. A Variable wind group is
reported when the direction varies by 60ø or more when the average wind speed is greather than 6
knots; or if the wind speed is less than or equal to 6 knots.
Example: 21016G24KT 180V240=Winds are from 210 degrees at 16 knots with gusts to 24 knots.
The wind direction varies from 180 to 240 degrees. If winds less than or equal to 6 knots; VRB05KT,
etc., without the degrees of variance.

And 8 pages later:
VOICE MESSAGES
ASOS computer-generated voice message are made available through telephone dial-in access and
are broadcast directly to pilots via ground-to-air radio (where installed). The information contained
in the ground-to-air radio broadcast message and the telephone dial-in message are identical. The
voice message is composed of the body of the ASOS observation and selected remarks. Selected
remarks can include variable visibility, tower visibility, or Density Altitude when 1,000 or more feet
above airport elevation. Control tower personnel may add Notice to Airmen (NOTAM) or other
information. Note that wind direction in the voice message is given in degrees magnetic.
 
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