In several places in the Days Gone, you may encounter seemingly inaccessible wreckages of helicopters. From this page you will learn what you requirements you need to complete to get to the wrecks and be able to search the area around them.
The wreckage of the helicopters can be found in some of the places that are marked on the map in the form of NERO Research Site. An example of this type of site is shown in the attached picture - it is a research facility southeast of the Copeland camp.
Upon arrival, you will notice that the helicopter is behind a small precipice. Deacon can't jump or climb to get there.
The solution to this problem, fortunately, is relatively simple - you need to equip Deacon's motorcycle with nitro. Check our information about upgrading motorcycle in a specific section of our guide - How to unlock nitro?. To remind you - you have to buy nitro from the mechanic after Deacon gets fairly high level of trust in the camp.
After installing nitro return to one of the helicopters. Accelerate a lot and activate the nitro while driving fast. The motorcycle should easily jump over a small abyss, and you will get to a new place.
Each point of NERO's research site allows you to find a injection that constantly increases Deacon's health, stamina or focus. It is worth visiting all these places immediately after the installation of the first generation of nitro.