Get the plane or helicopter tool. Sit in the plane's seat. You can now use the following controls.

Code	Effect
B	Drop bombs
F	Fire guns
Mouse Down	Tilt plane down
Mouse Left	Tilt plane left
Mouse Right	Tilt plane right
Mouse Up	Tilt plane up
T	180 degrees turn
X	Land plane
Y	Start plane
[Space]	Ejector seat