If you want to start simple, have a speed variable, and add 1 to it if the speed up key is pressed, or subtract 1 if the slowdown/reverse key is pressed. Make use of the move entity and rotateentity commands. They will calculate all the vector stuff for you :o)
TIP:
Use RotateEntity instead of TurnEntity. It rotates a better way.
XROt, YROT and ZROT are the amount you wish to turn on each axis :o)
TIP:
Use RotateEntity instead of TurnEntity. It rotates a better way.
RotateEntity plane , EntityPitch(plane) + XROT , EntityYaw(plane) + YROT , EntityRoll(plane) + ZROT
XROt, YROT and ZROT are the amount you wish to turn on each axis :o)