Stan Gosnell writes:

My understanding is that WAAS has an integrety function and is able to
detect an inaccurate signal.

RAIM (Receiver Autonomous Integrity Monitoring) is available without WAAS,
and was available before WAAS was implemented.

Look up FDE "fault detection / exclusion" instead. This computation
is possible to perform without WAAS (the GNS430 does some now), but
WAAS carries satellite health flags that simplify it.


- FChE