Facebook's solar-powered internet drone Aquila crashed during its inaugural test flight in Yuma, Arizona this summer due to strong winds, federal investigators concluded on Friday. According to a report released by the National Transportation Safety Board, the drone encountered an unexpected, powerful gust of wind as it came in for a landing that made it difficult for the unmanned drone to maintain its correct angle of descent.
In a blog post, Facebook said that in the final seconds of the flight, the aircraft flew into "higher-than-expected wind conditions" as it was descending that lifted the craft above its glidepath. The autopilot then responded by lowering the nose of the aircraft down to compensate and lifted the flaps called elevons on its wings upward.
"The combination of high airspeed, up elevon, and low angle of attack resulted in increased downward downward lift (and torsion) on the outer wing panels," the NTSB's report reads. "This loading exceeded its structural limit and resulted in a downward deformation and failure of the right wing." There were no injuries or ground damage in the crash.
According to Facebook, 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."
The social media giant said they are already working on incorporating possible fixes in future designs and flight tests including a drag device that allows the drone to descend without increasing airspeed.
"We are already designing and building second-generation aircraft with new features added as a result of our learnings, and are eager to fly again," Facebook said. "Each successive test flight will bring both expected and unexpected technical challenges, and will teach us more about how to fly this experimental aircraft.
The Aquila drone, which has a wingspan wider than a Boeing 737 at 141 feet (43m), was built with carbon fiber and weighs around 900 pounds (408kg). During the test flight on 28 June, the aircraft remained aloft at low altitudes for over 90 minutes, longer than the team expected time of 30 minutes.
Facebook expects its Aquila drones to stay airborne for up to 90 days at a time and provide broadband coverage to remote areas without reliable access to internet.
Although the crash was a setback in the Facebook's plans to bring internet access to areas around the world through its Internet.org initiative, the company did call the test flight a success in July despite the structural failure just before landing.
"Providing connectivity with solar-powered aircraft is something that hasn't been done before, and there are still a lot of hard science and engineering problems to solve," Facebook said. "This is a hard, years-long challenge, and things will break along the way ó that's the nature of engineering. Our results from the first test flight have solidified our confidence in the Aquila program and what we can potentially achieve with this technology.
"We intend to push the plan to its limits so we can learn more, learn faster, and reach our ultimate goal of connecting people sooner."