GPS gives the IFD the System time displayed in UTC (Universal Time Component), but the IFD also has an internal clock; in case the IFD is not getting GPS time from satellites, the IFD can still display this system time.
Internal clock time is updated from the GPS. If the IFD sits for long periods of time without being powered up, it is possible for the displayed system time to be off considerably until the unit receives GPS signal again.
This can be especially noticeable in dual IFD installations when the System time is off by a considerable number before receiving GPS signals to update the time:
When this happens, you may see the 'UTC Mismatch' CAS message and associated expanded message on the Alerts page:
The remedy for this is to make sure the IFD is receiving GPS signals so that the System Time can be updated. As the above excerpt from the IFD Pilot Guide suggests, power cycling the IFD will also update the time.
There may be instances where the IFD will not update the system time regardless of power cycles or GPS reception. If the UTC Mismatch in the Alerts Page remains active, or continues through power cycles, contact your Avidyne Dealer.