Cliffhanger

Rangers Gabriel "Gabe" Walker and Jessie Deighan are dispatched to rescue their friend Hal Tucker and his girlfriend Sarah after Hal suffered a knee injury and stranded them on a peak in the Colorado Rockies. As they try to rescue Sarah, part of her harness breaks, and though Gabe is able to grab her, her gloved hand slips out, and she falls to her death. Hal blames Gabe for her death and Gabe is overcome with guilt, taking an extended leave.
Eight months later, Gabe returns to the ranger station to gather his remaining possessions and convince Jessie to leave with him. While there, they receive a distress call from a group of stranded climbers. Hal goes to locate the climbers and Jessie is able to convince Gabe to help out. Hal remains bitter towards Gabe over Sarah's death, at one point threatening to send Gabe over a ledge. When they find the climbers, they discover the distress call was a ruse and are taken prisoner by former Military Intelligence operative Eric Qualen and several mercenaries. Qualen, along with turncoat U.S. Treasury agent Richard Travers, were able to steal three suitcases full of uncirculated bills valuing over $100 million. Their escape plan backfired, sending their plane crashing into the mountain, and they now require Gabe and Hal's help to locate the cases with the help of beacon locators.
At gunpoint, Gabe leads them to the first case, located at the top of a steep rock face. They force Gabe to tether himself to reach it, and Gabe uses the opportunity to escape. The mercenaries attempt to fire on Gabe, which causes an avalanche that kills one of their members. When they see the money from the first case fluttering away, Qualen believes Gabe is dead, and orders Hal to lead them onward. Gabe races ahead to find Jessie at an abandoned cabin. They recover old mountaineering gear to reach the second case before Qualen does. By the time Qualen arrives, Gabe and Jessie have emptied the case and left only a single bill with the taunting message "Want to trade?" on it. Qualen orders his men to split up, allowing Gabe to dispatch two more of Qualen's men. Gabe attempts to call for help from Frank, their rescue helicopter pilot, on one of the mercenaries' radios, but Hal alerts him to explosives Qualen has rigged above them on the mountain. Gabe and Jessie escape the falling debris in time. Elsewhere, when Hal sees two friends, Evan and Brett, he warns them away before Qualen orders his men to open fire. Brett is killed while Evan is wounded, though he manages to ski off the mountain and parachute to safety. Night falls on the mountain and both groups take shelter. Frank, having not heard from Gabe or the others, scouts the mountain in the helicopter, spots Evan's parachute, and is able to get him to safety while contacting the authorities.
When morning breaks, Gabe and Jessie beat Qualen to the last case. Meanwhile, the mercenaries flag down Frank in the helicopter, and by the time he realizes it's a trap it is too late. He is shot by one of the mercenaries and dies, but not before slipping Hal a knife. As the mercenaries split up to look for the other case, Hal is able to use the knife to wound one of the mercenaries, kill him with his own gun, and escape. Elsewhere Hal finds Gabe, and together they kill Travers. However, at the same time, Qualen takes Jessie hostage when she waves down the helicopter, believing that Frank was flying it. Qualen tells Gabe and Hal over the radio that he is holding Jessie captive on board the helicopter, demanding Gabe and Hal to surrender the money from the third case at a high elevated rendezvous point and threatens to kill her should they refuse to cooperate.
Gabe and Hal agree, and they meet at a cliff side bridge. However, Qualen tries to challenge Gabe into throwing the case into the helicopter, but when he also threatens to kill Jessie again, Gabe orders Qualen to free her at a safe distance away from the cliff. Qualen reluctantly agrees, and uses a winch to lower Jessie to the ground. Once Jessie is safely down, however, Gabe throws the bag of money into the helicopter's rotors, shredding the money. Enraged, Qualen attempts to fly off, but Gabe has used the winch cable to tether the helicopter to a steel ladder up the cliff face. The ladder snaps and leaves Gabe and Qualen atop the wreckage of the helicopter hanging by the cable. Gabe fights Qualen and manages to climb to safety as the wreckage snaps off the cable, sending Qualen to his death. Gabe reunites with Jessie and Hal as federal agents arrive in helicopters to offer their assistance.

Question: In the movie, who shoots Frank, resulting in his death?
Answer: one of the mercenaries