3-8
Climb-out/Enroute
the active flight plan or if additional/different altitude constraints
are desired, use the IFD flight plan edit controls to adjust the
vertical constraint field of a flight plan leg. “At”, “At or Below”, “At
or Above”, and “Window” constraints are all supported within the
FMS but the VNAV calculation will attempt to reach the waypoint
right “at” the constraint. An example of the FMS altitude
constraint field is shown immediately below.
VNAV will plan and attempt to meet constraints using the
preferred climb/descent rate, but will adjust as necessary up to
the maximum rate. The default descent/climb rate for all VNAV
operations is 500 fpm. If a different default rate is desired, the
FMS Setup pages can be used to set a new value (up to 1500
fpm) but this is not recommended by Avidyne. Maximum rates
may also be modified, but you should always be sure to leave at
least a 250 FPM difference from the preferred rate so that VNAV
has a margin for control. If the two rates are too close together,
VNAV will have little to no margin and the “VNAV Unable
Constraint” alert will be a frequent occurrence.
The FMS-computed VNAV target altitude is depicted on the
altimeter tape as a magenta diamond as shown in the image
below. The green VSR diamond on the VSI scale is advisory only.
