When Eddie is leaving the terminal, he has the bag from the locker in his hand (meaning the locker key was back in place). A few seconds later as Mannix is chasing him, the bag has disappeared and all he has is the key to the locker, which he drops.
At about 31 minutes the helicopter is not running, but then started up and was able to take off in a very short time allowing the escape. In reality, it would take quite a bit more time for the main rotor blades to get up to the proper speed, and Mannix would have had plenty of time to catch the pilot before the helicopter was ready to take off.
Mannix fires a total of 7 rounds from his 6 shot revolver without reloading.