Instructions
Download a mod called "Halo: Combat Evolved Custom Edition." This is a free, very large download made by "Halo" players. You can find the download on the CNET Downloads site.
Create a separate folder for "Halo: Combat Evolved Custom Edition." Install the program in this folder so that it doesn't interfere with the official game. You will need a "Halo" installation key to install the program.
Download a "Custom Edition" map called "Hugeass," easily found through an Internet search. This is a large, player-made map with a pair of bases that house several vehicles. The resultant download should be in a ZIP file.
Open the ZIP file. Look for a file called hugeass.map.
Open the "Maps" folder within the "Halo: Combat Evolved Custom Edition" folder. Drag the hugeass.map file into this folder.
Begin playing "Halo: Combat Evolved Custom Edition." Begin a multiplayer game and select the map file. Select the game type.
Start the game. You will be in one of the hangers within the map. Find the Pelican ship and climb through the back. At the pilot's seat, press the "E" key to begin flying the ship.