I won't give you the exact answers but I will point you in the right direction.
You're going to want to learn about the Distance() expression. This is used to determine the distance between 2 objects. If your helicopter is close enough to the POW's then they should run towards the helicopter.
Also, you will probably use the On collision with object event as well. When the pow's overlap with the helicopter, you'd add how many he picked up to a variable maxing out at however many he can hold before having to fly away again.
once he lands on the helipad to drop them off you can start subtracting how many he's holding, then spawn the animations of them running off to safety.
Just try breaking down each little element then searching the forums for examples or trying some things out in the engine to see how to get them to work.
Try bringing up the available events for a sprite for example and look through each of the possible actions. Ask yourself how you can use each one for different types of scenarios and you'll start to see how powerful the engine is, and the possibilities that are endless.