Here is the official FAQ answer on using a stall maneuver before or after an Immelmann ...
Q) Can you play a stall (that goes straight ahead) just before or after an Immelmann Turn?
A) No. Rules says: "You have to play a straight move (one with the *little arrow pointing up*
symbol) just before the Immelmann Turn and one just after". If you look carefully, you notice that
the stall has only a little diamond, not a little arrow pointing up.