ALTSEL and VNAV altitude limits
FSS says ALTSEL can limit the FMS altitude target during VNAV climb and descent. Check the selected value, the FMA and the aircraft response. A path on the map does not authorize descent below your clearance.
Descent clearance
Review the arrival, altitude constraints and intended clearance. Confirm performance initialization and find the predicted TOD.
Select the cleared altitude
When authorized in your simulation, set the next cleared altitude. Check the number in the selector and the present aircraft altitude.
Arm and observe
Select FMS as the navigation source and use VNAV for the phase. Watch PTH arm and capture. FSS says switching the navigation source away from FMS cancels VNAV and reverts to green FPA; after any source change, check the vertical FMA and flight path.
Vertical path capture
Watch speed, vertical deviation and the FMA. An armed path is not yet a captured path.
Altitude constraint
Check whether the aircraft captures and holds as expected. Obtain or simulate the next clearance and set the next authorized altitude.
If the path is unsuitable
Choose an appropriate selected mode, control speed and monitor terrain and constraints. Reassess rather than repeatedly pressing VNAV.
FSS says VNAV respects ALTSEL except in GS and GP. Its vertical-modes page adds that ALTSEL limits an FMS target when the selected altitude lies between the aircraft altitude and the FMS target. ALTSEL is a limit, not an altitude-hold mode. Read the FMA after selecting VNAV and check that the aircraft actually captures the expected altitude. For GS or GP, ALTSEL is ignored; set the missed-approach altitude after the approach mode captures. FSS vertical modes [38].
A community-support thread describes a possible exception: during an EHAM STAR, the aircraft reportedly descended below a selected 7,000 ft after passing SUGOL and going direct to OSRON. The poster recalled PATH on the FMA but was unsure whether ALT hold was active; another user reported similar behaviour elsewhere. The aircraft version, exact mode and cause were not established. Treat it as unresolved. If the aircraft leaves a cleared altitude, check the active route and FMA, then use a suitable mode or manual control to remain within the clearance. Community-support thread, 22 October–4 November 2026 [69].
When VNAV is selected in flight, the FMA depends on the flight phase and the FMS target. FSS describes magenta ALT when the aircraft is within 25 ft of that target. During a descent in cruise, descent or approach with LNAV active, PTH is armed; otherwise the FMS commands magenta FLCH. Check the FMA after selecting VNAV. FSS vertical modes [38].
FSS says GS and GP can continue with the missed-approach altitude set in ALTSEL. The page describes setting that altitude after capture. Verify the actual approach guidance and build. [38]