![]() If Airliner-VNAV is selected (dataref sim/cockpit2/autopilot/fms_vnav or command sim/autopilot/FMS) and the plane comes close to the top-of-descent: The behavior of the airliner FMS depends on the per-airplane setting “auto-arm VNAV descent” which is found on the autopilot settings page of Plane Maker. Thus, a new descent segment will be captured automatically. If the lebel off is caused by the VNAV target altitude, the indicated level-off will be “ALTV” and VNAV will revert to armed.For a subsequent descent segment, VNAV needs to be re-armed. ![]() If the level off is caused by a pilot-selected altitude, the indicated level-off will be “ALTS” (selected) and VNAV will be disarmed.The autopilot will level off at the higher of pre-selected altitude (sim/cockpit2/autopilot/altitude_dial_ft) and VNAV target altitude(sim/cockpit2/autopilot/altitude_vnav_ft): The descent rate will be modulated according to the forward speed and the vertical track error. If the vertical track is intercepted within the time limit, VNAV will engage and follow the vertical path angle (sim/cockpit2/radios/indicators/fms_vpa_pilot) down to the flight plan target altitude (im/cockpit2/radios/indicators/fms_fpta_pilot). VNAV will not intercept a vertical track after that time, it needs to be re-armed in this case. Also, the vertical track must be intercepted within 5 minutes (300 seconds) from arming VNAV. The autopilot will monitor the vertical track error (sim/cockpit2/radios/indicators/fms_vtk_pilot) which must be intercepted from below. The dataref sim/cockpit2/autopilot/vnav_status will indicate 1 for armed. VNAV descent works by arming the VNV PTH function on the G1000 by pressing the VNV button (sim/autopilot/vnav). VNAV will be altitude hold on the vertical axis, and speed or mach hold on the auto throttle axis. If the selected cruise-altitude has been reached, the FMS goes into cruise phase. Upon level-off, the next climb will be automatic if the level-off was due to a VNAV restriction (ALTV) or must be initiated manually by altitude intervention if the level-off was due to pilot pre-selected altitude (ALTS). The target speed is provided by the FMS, and the target altitude will be the lower of sim/cockpit2/autopilot/altitude_dial_ft and sim/cockpit2/autopilot/altitude_vnav_ft. Upon selection in the climb phase, the autopilot vertical axis will be speed-by-pitch, and the autothrottle will go to REF mode. ![]() VNAV climb and cruiseįor Airliner-VNAV to be selected (dataref sim/cockpit2/autopilot/fms_vnav or command sim/autopilot/FMS) in the climb or cruise phase requires the plane to have auto-throttle. “Airliner” with auto-throttle uses the auto-throttle to set climb power in climb, hold the selected cruise speed in cruise, and comply with speed restrictions (if physically achievable) in descend. “GA” without auto throttle can only do geometric descents – the vertical path is controlled by the autopilot, while the pilot controls the speed by the throttle (or speedbrakes). The main difference is the availability of auto-throttle. X-Plane knows two different types of VNAV, which can be described as “GA” and “Airliner”-type VNAV.
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