This dataref summarizes all of the possible state for the autopilot. The return value is a series of bit flags, as follows:
1 autothrottle 2 heading hold 4 wing leveler on 8 airspeed hold 16 vvi climb 32 altitude hold armed* 64 level change 128 auto-sync 256 hnav armed 512 hnav engaged 1024 gls armed** 2048 gls engaged** (X-Plane 8.11 and newer only) 4096 fms vnav armed 8192 fms vnav engaged 16384 altitude hold engaged
- Before 8.11 altitude was always 'armed'. In 8.11 the altitude becomes 'engaged' when level and not climbing to that altitude.
- Before 8.11 FMS vertical was the same as glide slope.
Some bitflags will never occur together. For example, vnav cannot be engaged and armed at the same time.
In X-Plane 7.10-7.30 you __cannot__ change the autopilot mode by writing this dataref. Instead use XPLMCommandKeyStroke to send the appropriate key stroke commands to the sim to engage the autopilot in various ways.
X-Plane 860: airspeed hold no longer exists separately from level change. For now airspeed mode is aliased to level change.
! Setting the autopilot in 7.40.
Starting with X-PLane 7.40 you can write to this dataref to activate the autopilot. Write to the dataref with the bit set for each function you want to simulate a press to. (In other words, if alt hold is on and you want to turn on heading, just write the heading bit; you don't need to set the alt hold bit too.) Some functions will toggle depending on the autopilot...the rules are the same as for users hand-controlling the autopilot. For HNAV and VNAV, write using the "armed" enums, because you are arming the autopilot. (You can't engage it, that happens when the signal is picked up and GS/loc are passed.)
Generally if a command key press and a dataref exist for the autopilot - use the command key press. It will be compatible with more versions of X-Pane.
! Deprecated Datarefs
These are the enum mappings for the older datarefs. Please avoid using them whenever possible; they will be discontinued!
sim/cockpit/autopilot/airspeed_mode 9 = discon 10 = autothrottle 13 = airspeed via pitch sim/cockpit/autopilot/heading_mode 9 = discoin 11 = heading mode 12 = wing leveler sim/cockpit/autopilot/altitude_mode 9 = discon 14 = vvi 15 = alt mode arm 16 = alt hold engage 17 = fms arm 18 = fms engage 19 = lca 20 = pitch sync sim/cockpit/autopilot/mode_hnav 9 = discon 21 = loc arm 22 = loc engage sim/cockpit/autopilot/altitude_gls 9 = discon 23 = gls arm 24 = gls engage