The National Transportation Safety Board (NTBS) is investigating an accident involving the inaugural flight of Facebook's massive experimental drone, designed to bring internet access to remote areas across the world. The solar-powered drone called Aquila suffered a "structural failure" as it was coming in for a landing in Yuma, Arizona during a test flight on 28 June, Bloomberg reports. No one was hurt in the crash.

"We were happy with the successful first test flight and were able to verify several performance models and components including aerodynamics, batteries, control systems and crew training, with no major unexpected results," Facebook said in a statement.

Although Facebook was pleased with the successful test flight, it said in July that its drone suffered a structural failure just before landing.

NTSB spokesman Peter Knudson told Bloomberg that the accident occurred at 7.43am local time, classifying the failure as an accident which means the damage was "substantial". However, he said there was "no damage on the ground". The NTSB has not yet released their findings about the incident, the extent of the damage or cause of the failure.

"We gathered lots of data about our models and the aircraft structure - and after two years of development, it was emotional to see Aquila actually get off the ground," Zuckerberg wrote in a post published on 21 July.

"But as big as this milestone is, we still have a lot of work to do. Eventually, our goal is to have a fleet of Aquilas flying together at 60,000 feet, communicating with each other with lasers and staying aloft for months at a time - something that's never been done before. To get there, we need to solve some difficult engineering challenges," he added.

Built with carbon fiber and weighing around 900 pounds (408kg), Facebook's Aquila drone has a wingspan wider than a Boeing 737 at 141 feet (43m). It remained aloft at low altitudes for 96 minutes, more than an hour longer than Facebook initially planned. The company expects these drones to stay airborne for up to 90 days at a time and provide broadband coverage within a 60-mile area on the ground, once they are fully operational.

The accident has caused a hitch in Facebook's ambitious plans to extend internet availability across the globe through the Internet.org initiative.

Facebook's $200m (£160m) satellite, which aimed to extend internet access in Africa, the Middle East and Europe, was destroyed in a SpaceX rocket explosion in September. Zuckerberg had at the time said he was "deeply disappointed to hear that SpaceX's launch failure destroyed our satellite" and added that it would have "provided connectivity to so many entrepreneurs and everyone else across the continent".