BENDIXKing AeroNav 910 Pilot's Manual page 122

AeroNav 900/880 Series Pilot's Guide
To generate the TOD feature:

There must be an altitude constraint defined on at least
one down-path waypoint at least 50' below present
altitude

There must be a valid GPS MSL Altitude or Baro Altitude

The aircraft is less than 2nm from the active leg
centerline

Aircraft course is within 45 degrees of Desired Track
(DTK)
The TOD function is not available on any waypoint of an
approach past the Final Approach Fix (FAF), or in holds, or
procedures turns.
The FMS uses a default of 500 feet per minute descent rate (or
as edited in the "Preferred Descent Rate" field on the FMS Setup
page). Keep these the same values in dual AeroNav installations.
There is an associated tone (sounds like a door bell and requires
wiring to the audio panel) and CAS countdown message 10
seconds prior to reaching the TOD point.
The "TOD" label may be auto-decluttered from the map
depending on map range and feature density. The TOD depiction
and CAS message are removed from the map immediately after
passing the TOD point.
Top of Descent (TOD) Marker
3-28 FMS Subsystem
89000039-010
Rev 1 May 2019