Altitude constraints and ALTSEL

The FMS may target a waypoint constraint before the altitude selected on the guidance panel. The two values have different origins and must both be understood. The map above shows an example descent profile; check the constraint and selected altitude on your own displays.

Read the constraint

Check the waypoint and altitude in FPL against the chart and clearance.

Read ALTSEL

Confirm the independently selected altitude on the guidance panel and PFD.

Compare the targets

FSS describes a VNAV waypoint-constraint readout and a target-altitude bug when valid and FMS is the selected source.

Watch the mode

Monitor the FMA as the aircraft approaches and captures the relevant target.

Next altitude clearance

After a level-off, do not assume VNAV will continue through ALTSEL. Select the next cleared altitude and verify the resulting guidance. ^[201]