Press [T] for the message prompt and type:

 you got what i need  - Unlimited ammo
 food goes here       - Reload plane
 big gulp             - Refuel plane
 youre here forever   - Invincible
 damn that corner     - Can't crash
 chiliburger          - Repair plane
 spindive             - Can't be hit
 upside down          - Auto level fly upside down
 paperairplane        - Paper airplane
 patsux               - Unknown

 (Same Cheats also work for Mig 29 Fulcrum)