Pitch and Z-velocity

[Devastator_cm 434]

Does anybody knows how setting the velocity at Z angle adjusts the pitch angle of fixed wings?

 

Example code is below

 

private _AirCraft = vehicle player;

while {alive _AirCraft} do

{
	_AirCraft setVelocity [(velocity _AirCraft select 0), (velocity _AirCraft select 1), 10];	

};

when I run this code by airplanes is is auto adjusting the pitch angle. I only had one modded airplane where this didn't work and I wonder why...