No cheat spawns a jet in GTA IV. The cheat list is limited to health, armor, weapons, vehicles (cars/boats/helicopters), and wanted level.
How to Get a Jet Legitimately
Story Progression: Unlocks access to Francis International Airport tarmac (post-Final Interview mission).
Steal at Airport:Shamal (business jet) and 747-esque "Airliner" (unflyable) spawn near hangars. Heavily guarded—expect 4-star wanted level.
Helicopter Alternative:Annihilator (attack heli) spawns on police helipad (East Holland, Algonquin) after Certain missions or 4-star wanted. Easier to steal.
PC Mods:Simple Native Trainer, Menyoo, or vehicle spawn mods add any aircraft (Hydra, P-996 Lazer, etc.).
GTA IV vs. V: GTA V has the Skyfall cheat (spawn mid-air) and Buzzard/ Lazer spawn codes. IV does not.