On Jan 25, 11:47 am, "Bill Denton" wrote:
Keep in mind that there is a difference between "valid" and "correct".

For example, a computer program may require that a number be entered in a
specific field.

Any number that is entered would be "valid", but it would not necessarily be
"correct".

A given electronic device might cause a reading to be 10 degrees off. The
nav system might well interpret the data as "valid" even though it would not
be correct.

Agreed. However, having a choice of signals to "believe," the FMS
should have an integrity check in its logic, right? If the VOR-NAV is
showing you 3 miles to the left of the localizer and the GPS and INS
are showing you on it, then the FMS should disregard the VOR-NAV.

Also, there may be other ways of verifying integrity such as the
presence of wild fluctuations in a given period of time.

Marco