What goes up doesn’t necessarily come down in one piece. That’s what Facebook seems to be finding out during its tests of prototype systems designed to get the world online.

The social network cooed when its stratospheric Internet-spewing drone, Aquila, took to the skies for the first time back in July. But while the test flight lasted three times longer than planned, it didn’t end so well. Facebook engineers noted at the time that the aircraft suffered a “structural failure” during the flight. But according to Bloomberg, the National Transportation Safety Board has been investigating the incident, and now says that the aircraft experienced “substantial” damage.

It’s the second big setback for Facebook’s plans to bathe the planet in Internet access. Back in September, a SpaceX rocket containing the Amos 6 communications satellite exploded on the launchpad. A large chunk of the satellite’s spectrum was reserved for use by Facebook as part of its plan to roll out wireless broadband across the globe. The explosion has since been found to be the result of a fueling problem, but that’s no consolation to Mark Zuckerberg, who at the time said that “the problem isn’t the money; it’s that now it may take longer to connect people.”

Clearly, Zuckerberg is feeling the frustration that comes with testing exotic hardware. (It’s almost as if it’s more difficult than building a website.)

Still, it’s understandable: two-thirds of the company’s three-part plan to connect the world is now mired in technical issues. The third route to providing a global Internet, by the way, is a new breed of wireless networks. At least they don’t need to be airborne.

(Read more: Bloomberg, The New Yorker, “Facebook’s Three-Point Plan to Get Four Billion More People Online,” “Facebook Is Testing a Super-Speed Public Wi-Fi System,” “Meet Facebook’s Stratospheric Internet Drone”)