The Helicopter Mercs were mercenaries in the employ of Eli Mills. They rode in a helicopter and participated in the mission to retrieve a piece of the skeleton of the Indominus rex. There were three of them in addition to the team leader and the group's pilot. Among them was Jack.
When Jack lost communications with Marine One, the helicopter mercs tried to warn him of something approaching from the jungle. However, over the noise of the helicopter and the storm, Jack failed to hear them. When Isla Nublar's resident Tyrannosaurus rex attacked Jack and pursued him down Main Street, the helicopter took off to avoid getting attacked. The mercenaries tossed a ladder to help Jack, but halfway through Jack's climb, the T-Rex caught the ladder in its jaws.
The lead mercenary ordered the mercs to cut the ladder and leave Jack to die so they could extract with the Indominus rex bone. However, conflict broke out among the mercenaries as one of them tried to stop another from cutting the ladder with a knife, hoping to get Jack on the chopper in one piece. After the lead mercenary loudly repeated the order, the ladder broke and the helicopter was freed, making it seem like Jack would survive the mission.
This relief would be short-lived, as the Mosasaurus lurking in the lagoon below breached the water and snapped Jack up immediately. While some of the mercenaries stared at the water in horror and disbelief, another reported that the mission to retrieve the bone was a success and the helicopter proceeded to leave the island.