If the IFD is interfaced with a GAD29/29B/42/43. There could be an instance where the IFD will display:

 

 

The first thing that should be checked is the configuration. If the GAD is interfaced with a Garmin AP then the appropriate RS-232 setting should be EFIS/AIRDATA. If the GAD is interfaced to a 3rd party AP, the correct configuration is GAD42. This RS-232 configuration will cause this CAS message to display if the configuration is incorrect. If this does not solve the issue then continue below.

 

The GAD outputs maintenance/ status labels 270 and 271 over the ARINC429 Line. 

 

270:

RAM Failure

ROM Failure

XILINX 1 Failure

XILINX 2 Failure

Configuration Required

Calibration Required

 

271:

Backup Supply Failure

20 V Supply Failure

12 V Supply Failure

+5 V Supply Failure

-5 V Supply Failure

-12 V Supply Failure

-20 V Supply Failure

 

If these labels are broadcasted, the IFD5XX/4XX will display the above CAS Advisory. 

 

This message means there is an internal supply voltage failure or calibration data is not valid in the GAD and the component needs to be returned to GARMIN for Repair.