Abnormal Procedures
5-21
AHRS MISCOMP
In Cirrus SR2X or Piper PA46 installations where the DFC90 is
replacing a STec 55X autopilot, the DFC90 will use the previously
installed turn coordinator as a source of attitude comparison. In
all other cases, there is no connectivity to a turn coordinator and
this scenario does not apply.
Failure Indication:
If the DFC-PFD system recognizes that a miscompare condition
is active between the PFD AHRS and the blind-mounted turn
coordinator
, a yellow “
AHRS MISCOMP
” message is displayed
on the PFD. This display alert is accompanied by a single aural
alert “GYRO MISCOMPARE” that is audible in the headsets. The
autopilot should not disengage under this condition.
Functionality Lost:
If on the ground, the autopilot will not allow engagement in any
mode with this condition.
If a miscompare condition is experienced at any time after initially
engaging the autopilot in any mode, then the only autopilot
functionality that has been lost is the automatic, behind-the-
scenes comparator that is running between the PFD AHRS and
the blind-mounted turn coordinator.
Recommended Pilot Action:
If on the ground during this condition, cycle power to the turn
coordinator by cycling the avionics master. This also has the
affect of cycling power to the autopilot itself which would clear any
false reports of AHRS-TC miscompares. If that was not
successful, plan your flight without autopilot.
If the alert is presented at some time after initial autopilot
engagement, evaluate the accuracy of the PFD AHRS solution by
comparing the PFD display to the backup gauges, and if in VMC
conditions, the out-the-window view. If it can be concluded that
the PFD is accurate, consider re-engaging the autopilot and
continue standard autopilot operations but be vigilant knowing
that the AHRS-TC comparator has noted a sensor miscompare.
Change 3