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Calculating Wind Speed And Direction  
User currently offlineTimRees From United Kingdom, joined Aug 2001, 354 posts, RR: 0
Posted (9 years 2 months 3 days 1 hour ago) and read 3729 times:

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.

5 replies: All unread, jump to last
 
User currently offlineGoldenshield From United States of America, joined Jan 2001, 5963 posts, RR: 14
Reply 1, posted (9 years 2 months 2 days 22 hours ago) and read 3696 times:

The GPS or INS takes and compares the following data:

Trajectory heading - actual heading
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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User currently offlinePihero From France, joined Jan 2005, 4383 posts, RR: 76
Reply 2, posted (9 years 2 months 2 days 20 hours ago) and read 3678 times:
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Goldenshield,

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

heading - actual TRACK
TRUE airspeed - groundspeed " ?

Regards



Contrail designer
User currently offlineGoldenshield From United States of America, joined Jan 2001, 5963 posts, RR: 14
Reply 3, posted (9 years 2 months 2 days 20 hours ago) and read 3675 times:

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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User currently offlineSaintsman From United Kingdom, joined Mar 2002, 2065 posts, RR: 2
Reply 4, posted (9 years 2 months 2 days 13 hours ago) and read 3649 times:

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  Wink


User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 5, posted (9 years 2 months 2 days 12 hours ago) and read 3655 times:

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?


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