Cirrus SR22 Pilot Operating Handbook page 281

Cirrus Design
SR22
message will be displayed on the PFDs and the vertical deviation
indicator (VDI) will be flagged. If SBAS is required for the approach,
the approach mode (e.g. LPV) will be shown in amber but the GPS/
SBAS VDI will be displayed until 60 seconds prior to the FAF. If the
SBAS integrity has not been restored at 60 seconds prior to the FAF,
the system will display the "APR DWNGRADE - Apr downgraded.
Baro VNAV." message and flag the VDI.
Once the pilot acknowledges either message by viewing it on the PFD,
the VDI will be restored using baro altitude vertical guidance instead of
SBAS. There is no downgrade from SBAS to barometric altitude after
the FAF or within 60 seconds of the FAF; "LNAV" is the only
downgrade option in those cases. For approaches using barometric
vertical guidance, downgrade is not allowed; if altitude or temperature
data becomes invalid, the vertical deviation will be flagged.
Sensor Failures
The Outside Air Temperature (OAT) from the selected-side Air Data
Computer will be used. If the OAT becomes invalid the VDI on that
side will be flagged as invalid. The crew must select the off-side Air
Data Computer sensor and VDI will return regardless of if prior to or
after the FAF.
Sensor Comparison Annunciation
The temperature compensated altitudes from the pilot and co-pilot
side are continuously compared. If a miscompare of greater than 50
feet is detected, the text "VDI MISCOMP" is displayed in the sensor
comparison annunciation area on the PFD in black text with an amber
background.
When a temperature-compensated altitude is not available for
comparison, a "VDI NO COMP" annunciation is posted in comparison
annunciation area on the PFD in black text with a white background.
P/N 13772-004 P/N 13772-004
Revision 1
Section 7
Systems Description
7-95 7-95