TimRees
Topic Author
Posts: 300
Joined: Thu Aug 02, 2001 2:09 am

### Calculating Wind Speed And Direction

I'm puzzled as to how when ATC ask an aircraft the outside wind speed and direction they simply 'read it back'.

Is this a function of pitot tubes (wasn't mentioned in the thread on them I read) or is it the INS or something I'm not aware of. As you can guess, I'm not a pilot.

Goldenshield
Posts: 5017
Joined: Sun Jan 14, 2001 3:45 pm

### RE: Calculating Wind Speed And Direction

The GPS or INS takes and compares the following data:

Actual airspeed - groundspeed

This will give you a simple wind. There are other factors taken into account as well for a more exact figure, such as altitude, OAT, etc.
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Pihero
Posts: 4292
Joined: Mon Jan 31, 2005 5:11 am

### RE: Calculating Wind Speed And Direction

Goldenshield,

Shouldn't it be :
"compares the following data :

TRUE airspeed - groundspeed " ?

Regards
Contrail designer

Goldenshield
Posts: 5017
Joined: Sun Jan 14, 2001 3:45 pm

### RE: Calculating Wind Speed And Direction

The heading part could be said either way, since you are correcting for drift, and, yes, true airspeed would be your actual indicated airspeed corrected for everything else, but I didn't want to get too in depth.

Basically, it's all triginometry in the end.
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saintsman
Posts: 2037
Joined: Fri Mar 15, 2002 12:34 am

### RE: Calculating Wind Speed And Direction

If they simply read it back then the information is on a screen in front of them, already worked out by one of the navigational computers.

Actually, I bet most airline pilots would have to think hard about working those figures out! It would have been a long time since they had to do it themselves

PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

### RE: Calculating Wind Speed And Direction

 Quoting Saintsman (Reply 4):Actually, I bet most airline pilots would have to think hard about working those figures out! It would have been a long time since they had to do it themselves

Don't bet too much. There are some of us who had that drilled into our heads in the military. I can still remember having to determine wind at altitude with only DME, and wizz wheel. Funny thing is somethings you never forget. Or perhaps having to do an ICE T speed calculation?
Fly fast, live slow

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