Johnson disappearing on Cairo Station is a glitch in Halo 2's Campaign level, Cairo Station. The glitch causes Sergeant Johnson to suddenly disappear during gameplay. It is easier if you get an Energy Sword from an Ultra Elite (Heroic or higher only), though this is not required.
Use the Energy Sword to slash Johnson in the direction of the airlock door that leads to the station's exterior and docking port. After killing the Rangers, continue to slash Johnson toward the fire control center. After you get Johnson in the elevator, he will disappear as soon as Fleet Admiral Harper starts talking.
- This glitch can also be performed with Miranda Keyes