Unfortunately there is not a cheat code in "GTA 4" that spawns an airplane. It is possible, however, to spawn a helicopter and can be done by dialing 359-555-0100 in the game.
Cheat codes are used in "GTA 4" by dialing numbers into the cell phone during game play. In addition to spawning a helicopter, there are several other cheat codes that aid players in the game. To regain health and armor, players dial 362-555-0100. To spawn advanced-tier weapons, players dial 486-555-0100. To remove the wanted level, players can dial 267-555-0100. Cheat codes are fun and helpful, but some disable the ability to unlock achievements or trophies. These features are disabled as long as the cheat remains active.