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The Perils of Unapproved GPS
by Shawn Coyle, Engineering Test Pilot, Transport Canada
Recently
one of our readers sent a letter outlining problems with a hand-held global
positioning system (GPS). Basically the problems were with the map display. It appears
this particular model showed highways in the incorrect location, and the Toronto
Island airport was shown far out into the lake. The manufacturer of the equipment
blamed the database (which they obtain from another supplier), but other hand-held
GPSs that use the same database were correct. What lessons are to be learned from
this? For those who supplement their IFR navigation with hand-held GPS units, remember
they are very different from IFR-approved GPS receivers. Hand-held GPSs are not subject
to any certification process, and while they are useful, they are not a substitute for
standard IFR navigation instruments or proper VFR map reading. Hand-held GPSs have no
self-monitoring to tell you that the satellite geometry may be less than optimum. There
have been reports of errors of up to 80 NM with hand-held GPSs. GPS is a very
useful tool, but it is not without its pitfalls.
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