Top of descent and ALTSEL

Select lower clearance

Before TOD, select the next cleared lower altitude when authorised in the simulation.

Complete PERF INIT and fly a simple route with a displayed top of descent. Confirm that FMS is the navigation source and that LNAV and VNAV are active.

ALTSEL as a limit

Watch the VTA, armed PTH, capture and the actual descent path.

FSS says VNAV respects ALTSEL except in GS and GP; its page describes ALTSEL as limiting an FMS target when the selected altitude lies between the aircraft altitude and FMS target.

FMS and ALTSEL

Check FMS source, active LNAV and VNAV, confirmed performance data, ALTSEL and actual vertical deviation. Treat the selected altitude as a limit, not proof that altitude hold is active.