This wild ascent begins at he Rattlesnake Trail Bridge, in the high northwest mountains of Jacob's patch.
The prepper note is at the end of the bridge.
Follow the path and the blue ropes up, until you near the broken bridge.
You can't climb up to the bridge from there, but you can swing underneath to a ledge north.
Then you can take the path up, and take down the hostiles at the bridge.
Jump over the bridge, and grapple up the next cliff. There's another, smaller broken bridge you can jump or swing over.
Just after that, you can grapple down to another set of ledges, though the wingsuit works even better.
Grapple up to the top, with the wreckage, and three looters. But not looters like you- evil looters.
Kill them, then find the key in a little manger past the tail of the plane.
Return to the fuselage and open the long box there to complete the stash.