The GTA: San Andreas mission where CJ steals a jetpack from Area 69 is called “Black Project.”
The mission is assigned by The Truth, an eccentric hippie who believes a secret military installation is developing extraordinary technology. He sends Carl “CJ” Johnson to infiltrate Area 69, a heavily guarded base in Bone County modeled on the real-world Area 51 conspiracy myth.
CJ must enter the underground facility, avoid or eliminate soldiers, work around searchlights, and reach the research laboratory before sunrise. Inside the base, he finds the Black Project: a jetpack stored in a launch bay. After taking it, CJ escapes through the opening above the bay and flies to a drop-off point in the desert.
The mission is often confused with “Up, Up and Away!”, another San Andreas mission involving a military base and a jetpack. However, “Up, Up and Away!” occurs later and involves stealing a military vehicle to obtain a high-value item. “Black Project” is the mission specifically centered on infiltrating Area 69 and acquiring the jetpack.