Thank you Pfeil,
i have understand, that's work now. I have add pauses between "turn on" and the GetValue, because value had not enough time to change, so, the value was always 0.
Now the code is like is and that's work:
Execute command, 'set adir display to s t s' (and wait until it completes)
Pause 0.5 seconds
Execute command, 'set adir system to one' (and wait until it completes)
Pause 0.5 seconds
Execute command, 'adir one on nav' (and wait until it completes)
Pause 0.5 seconds
Execute external plugin, 'SPAD.neXt VoiceAttack Plugin - v0.9.5+' and wait for return
Start Loop While : [xplane!sim/custom/xap/adirs/on_bat] Equals 1
Pause 0.5 seconds
Execute external plugin, 'SPAD.neXt VoiceAttack Plugin - v0.9.5+' and wait for return
Write '[Purple] xplane!sim/custom/xap/adirs/on_bat' to log
End Loop
Execute command, 'adir two on nav' (and wait until it completes)
Pause 0.5 seconds
Execute external plugin, 'SPAD.neXt VoiceAttack Plugin - v0.9.5+' and wait for return
Start Loop While : [xplane!sim/custom/xap/adirs/on_bat] Equals 1
Pause 0.5 seconds
Execute external plugin, 'SPAD.neXt VoiceAttack Plugin - v0.9.5+' and wait for return
End Loop
Execute command, 'adir three on nav' (and wait until it completes)
Pause 0.5 seconds
Execute external plugin, 'SPAD.neXt VoiceAttack Plugin - v0.9.5+' and wait for return
Start Loop While : [xplane!sim/custom/xap/adirs/on_bat] Equals 1
Pause 0.5 seconds
Execute external plugin, 'SPAD.neXt VoiceAttack Plugin - v0.9.5+' and wait for return
End Loop
Set decimal [xplane!sim/custom/xap/adirs/knob_ent] value to 1
Execute external plugin, 'SPAD.neXt VoiceAttack Plugin - v0.9.5+' and wait for return
thank you very much for your help.