Avidyne IFD410 FMS/GPS, Pilot'S Manual

Page: 287 / 380

IFD400 Series Pilot Guide
Navigation 5-35
ENROUTE VERTICAL NAVIGATION (VNAV)
The IFD is capable of providing vertical navigation during descent
operations.
Vertical navigation is driven by a “descent path” that
is defined by the altitude constraints in the flight plan and a
descent angle specified on the Setup page. When enroute VNAV
is active, the IFD will provide vertical deviations to the descent
path. The enroute VNAV capability must be enabled by the
installer after it is determined that the aircraft is equipped to
perform the function.
ALLOWING ENROUTE VNAV
The following conditions must be satisfied in order for enroute
VNAV to be allowed:

Enroute VNAV is enabled by the installer

The flight plan has an active leg

The aircraft is airborne

The IFD is receiving a valid baro corrected altitude
If enroute VNAV is not allowed, enroute vertical deviations will not
be generated. However, the IFD will still compute the top-of-
descent (TOD) point using VNAV descent angle or rate.
DEFINING THE ENROUTE VNAV ALTITUDE TARGET
Altitude constraints entered into the flight plan define the potential
altitude targets for enroute VNAV. The IFD evaluates each
successive leg of the flight plan, starting with the active leg, to
determine the active enroute VNAV altitude target. If the leg
begin evaluated meets any of the following criteria, the IFD stops
searching and there is no enroute VNAV altitude target:

The leg terminates at an altitude

The leg is a hold

The leg terminates at a FAF

The leg is preceded by a discontinuity (except the active
leg)
If the leg has an associated altitude constraint whose altitude is
lower than the aircraft altitude, the IFD uses that altitude as the