The following codes can be used when the the 'Invincible Aircraft' control setting has been enabled. Just enter them during flight to activate the corresponding cheat function.

Add 500 Feet to Altitude:
Press Ctrl + Tab

Slow Motion Mode:
Press Ctrl + Tab + S

Enable Joystick:
Press Ctrl + Tab + X

Press the 'P' key to pause the game and then enter the following case sensitive codes to enable the corresponding effect.

Get +1 Life - +9 Lives:
Enter LF1 - LF9

Kill 1 Enemy:
Enter Kil

Kill Enemies:
Enter All

Fly:
Enter FUS

Can't Jump (Fly Down):
Enter JDN

Walk (Fly Down):
FDN

Can Jump - Can't Jump:
Enter AJU - AJD

Keep Jumping:
Enter JUS

Go to Next Level:
Enter New

Slow 10 - Slow 30:
Enter SL1 - SL3

Speed 10 - Speed 30:
Enter SP1 - SP3

Stop 10 - Stop30
Enter ST1 - ST3