Avidyne IFD540 Pilot's Manual page 154

The GPS navigation states possible are:
GPS Navigation State
Self Test
Init
Search
Basic Nav
FDE Nav
SBAS Nav
Fault
The graphical bars represent the relative signal strength of each
individual SV as well as the SV identification number. SV
numbers above 100 represent the WAAS satellites. It typically
requires three WAAS satellites before full WAAS functionality can
be realized.
4-46 AUX Pages
Operational Meaning
System performing self test. This is
the initial state value but happens so
quickly it is rarely observed.
System is initializing – this state is
also very quick and is rarely
observed.
Satellite acquisition mode.
System has acquired enough
satellites to conduct basic navigation
but without integrity.
System has acquired enough
satellites to conduct navigation with
fault detection and exclusion integrity.
System is capable of navigation with
satellite-based augmentation (e.g. the
WAAS platform in the US).
System has detected an internal fault
and does not have a satellite
navigation solution.
This may require a manual power
cycle of the IFD to restore a GPS
lock.