See High altitude connectivity: The next chapter (Facebook Code blog) for more details
"Facebook said there are now other companies in aerospace that are investing in the same kind of technology. So it’s time for the company to step out of the race. Instead of building, Facebook said it will work with partners like Airbus SE on high-altitude connectivity technologies.Facebook Is No Longer Building an Internet-Beaming Aircraft -- Bloomberg
Though it ultimately didn’t live up to its ambitions in the skies, the Aquila drone served as a visible symbol of innovation at a company where all of the most important work usually happens behind the scenes, in lines of software code. The Aquila, demonstrated at Facebook’s conferences and, at one point, touted in an innovation lab at the company’s headquarters, was frequently held up as an example of the important work Facebook was doing as part of its mission to connect the world via the internet. The company is still working on other technologies that can spread online access."