Certain characters are unlocked at certain rank levels for play in Fragile Alliance.

When you are at the spot where you have to proceed to El Capacito, tell your men to go to the big pointy statue in the center and take cover. Then, proceed to shoot down the helicopter first before continuing. A few RPGs will be required before it will go down. If you run out of RPGs, go back to the previous spot where you had to shoot the APC vehicle to get more supplies.