5-10
Abnormal Procedures
VNAV Unable
Constraint
The system has determined that it can not
make the next vertical constraint. It may
be too close or require too much of a
climb or descent rate. Additional pilot
input may be required.
VNAV Unavailable
Message displayed when the VNAV
button on the autopilot has been pressed
but the system is not able to provide
VNAV because either Primary Nav is not
set to FMS, the autopilot is not in NAV
mode (engaged or armed), or there is no
down-path altitude constraint in the flight
plan.
VNAV Terminated
The system has transitioned out of VNAV
mode. This may be a normal operation
during VNAV descents to instrument
finals. The autopilot will typically
transition to ALT Hold in this case.
LOSS OF ENGINE
Loss of engine does not affect the DFC100 operation but the
DFC100 autopilot can be useful during loss of engine situations.
One technique is to set the IAS bug to best glide speed and
engage IAS mode in the event of engine-out conditions. The
autopilot will adjust aircraft pitch as required to slow down, or
speed up to achieve V
g
, freeing up time to perform other cockpit
duties during this emergency situation.
One minor variation of this technique is to set the IAS bug to V
g
after climb-out so that it is already preset to V
g
.
In either technique, it is recommended to press the “IAS” button
on the autopilot control panel a second time to prevent an
inadvertent altitude capture.
Envelope Protection will prevent the autopilot from stalling the
aircraft during power-off operations.