XPost: rec.aviation.piloting, alt.usenet.kooks   
   From: nospam@nospam.com   
      
   Bertie the Bunyip wrote:   
   > Flydive  wrote in news:460e0b75_5@news.bluewin.ch:   
   >   
   >> Bertie the Bunyip wrote:   
   >>> Mxsmanic  wrote in   
   >>> news:u1iru2lnv6plai306035nbplccc5o3480v@4ax.com:   
   >>>   
   >>>> Andy Hawkins writes:   
   >>>>   
   >>>>> Just out of interest, how do you measure speed on the ground?   
   >>>>> Obviously the airspeed indicator isn't much use in these   
   >>>>> situations...   
   >>>> If you have fancy avionics, they'll tell you your actual ground   
   > speed,   
   >>>> as read from an IRU or GPS.   
   >>> Says mr know nothing..   
   >>>   
   >>>   
   >>> Bertie   
   >>   
   >> But he is right   
   >>   
   >   
   > Not really. We use them as a rough guide but they're not all that   
   > reliable on the ground. Only as a guide. Older widebodies had ground   
   > speedos just like a car. Just a little clock on the capt's panel down   
   > the bottom, usually. All newer ones use IRS, but   
   > IRS info can be out by up to 10 knots by the time you land.  A   
   > negligable error in flight, but huge on the ground. Also fucks up your   
   > wind indications on appraoch. Not a problem for a pilot, BTW, but it   
   > does screw up the automatics if they get confused about the crosswind on   
   > some airplanes.   
   >  It's not uncommon for them to show movement while you're parked after a   
   > long flight particualrly if radio update isn't all the best towards the   
   > end. Like if you're flying into an area without a lot of DMEs. newer GPS   
   > stuff is better, but it's not really neccesary anyway except in 74's   
   > wher it's quite difficult to tell your GS.   
   >   
   >   
   >   
   > Bertie   
      
   True in part, the latest FMS use the GPS as primary source, so the GS   
   indication is quite accurate on the ground.   
      
   --- SoupGate-Win32 v1.05   
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