7-94 P/N 21399-004
Section 7 Cirrus Design
Airplane and Systems Description SR20
supported using Baro-VNAV. If Baro-VNAV can be supported, the
“APR ADVISORY - SBAS VNAV not available. Using Baro VNAV.”
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
Serials with single Air Data Computer (ADC) installations: The Outside
Air Temperature (OAT) from the ADC will be used. If the OAT becomes
invalid the VDI will be flagged as invalid.
Serials with dual Air Data Computer (ADC) installations: The Outside
Air Temperature (OAT) from the selected-side ADC will be used. If the
OAT becomes invalid the VDI on that side will be flagged as invalid.
The pilot must select the off-side ADC sensor and VDI will return
regardless of if prior to or after the FAF.
Sensor Comparison Annunciation
Serials with dual Air Data Computer (ADC) installations:
The temperature compensated altitudes from ADC1 and ADC2 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.
Revision A1
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