T&T: GPS Error

[Gil Johnson]

Here's a great example of problems that can occur with
your autopilot that can be catastrophic.

While cruising up the Potomac River with the AP
engaged our boat makes a hard turn to starboard, the
AP goes into alarm and disengages.  Luckily, the boat
coming our way was far enough out not to have anyone
panic.  After quickly putting the boat back on course
I checked what happened.  The rate compass was still
indicating the correct direction, but the GPS derived
course was indicating we were headed almost 180
degrees off of our actual course.

This occurred while one of the Marine One
(Presidential Helicopter) was landing at Quantico. 
This may have been coincidental, although we have had
GPS errors in this area before.  Those errors have
previously only been slight position accuracy errors.

The fix to the problem was to turn off the AP and turn
it back on.  Well, at least that did fix the problem
which may or may not have corrected itself over the
same distance the unit was off and powering back up.

So, the AP, like any other processor driven device can
fail you.

Gil


       
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