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​Facebook drone investigation: Wind gust led to broken wing

A wing on the internet-beaming aircraft broke when its autopilot tried to maintain its angle of descent, a US government report concludes.

Facebook's Aquila drone

Facebook/Screenshot by Stephen Shankland/CNET

Aquila, Facebook's internet-beaming drone prototype, was laid low because of an inability to handle a gust of wind, a federal investigation concluded, and Facebook is changing the aircraft design accordingly.

The drone, unmanned and operated by autopilot technology, crashed June 28 as it was coming in to land at the very end of its first test flight in Yuma, Arizona. Nobody was injured, but the aircraft was "substantially damaged," according to a National Transportation Safety Board report released Friday.

The stronger-than-expected wind gust made it hard for the drone to maintain its proper angle of descent, so its autopilot compensated by pointing the nose of the aircraft down, the NTSB said. To do so, it lifted up flaps called elevons on the trailing edge of its wing. That led to too much pressure and twisting for the lightweight aircraft to handle, the report said.

Facebook, keen to find new ways to bring internet access to people who can't easily get it today, still called the flight a success overall.

Another problem the crash showed is that the Aquila couldn't slow itself down enough through aerodynamic drag, the NTSB said.

Facebook concurred. "The autopilot was unable to track both the airspeed and glidepath simultaneously, and gave too much priority to tracking the glidepath at the expense of not limiting the airspeed," Facebook said in a blog post Friday. Future designs will include a mechanism to increase drag so the Aquila can descend without gaining too much speed.

Powered by solar energy and designed to circle overhead for 60 to 90 days at a time, the Aquila drone is part of Facebook's effort to boost broadband coverage to remote areas without traditional internet infrastructure. The Aquila crash was just one setback, though. In September, a satellite designed to bring internet access to parts of Africa courtesy of Facebook was destroyed when the SpaceX Falcon 9 rocket that was supposed to carry it into space exploded at Cape Canaveral, Florida.