There is no jetpack in the original programming for “Grand Theft Auto IV,” and no in-game codes or cheats exist to unlock one. Players on personal computers can install an external mod, such as the jetpack script mod, available at GTA4-Mods.com, but no similar method exists for console players.
To modify the PC game, you must first unlock it. Download and run a specialized patcher, such as GTA IV Modding Unlocker or GTA IV Magic Patcher, to back-up your game files, and prepare the game for modding. Download the mod file, and export it to the data folder under the common directory in your game folder.
When you start the game with the jetpack script mod, the Jetpack Kill Frenzy event is visible on the map. Navigate to the location, and activate the mission to use the jetpack. The timed mission requires you to use a rocket launcher to destroy 20 vehicles while flying with the jetpack.
The only game in the series to feature the jetpack officially is “Grand Theft Auto: San Andreas,” as of 2015. Some of the script for “Grand Theft Auto V” provides evidence that a jetpack was in development for the game, but there was no playable jetpack in the release version or subsequent content updates.