The National Transportation Safety Board (NTSB) confirms it is investigating the June crash of Facebook's unmanned Aquila aircraft, which the company is developing to bring internet access to remote regions.
The aircraft, registration N656AQ, "experienced an in-flight structural failure on approach near Yuma, Arizona", the NTSB tells FlightGlobal. "The aircraft was substantially damaged."
The incident happened on 28 June at 07:43 local time and did not cause any injuries or ground damage, the safety investigatory agency says.
News of the first flight broke when Facebook's creator Mark Zuckerberg posted about the test flight on his Facebook page on 21 July.
Zuckerberg's post said the 42m-wingspan solar-powered aircraft had a "successful first flight". It did not mention any failure.
However, also on 21 July Facebook posted a lengthy analysis about the flight on a separate webpage in which the company acknowledged a failure.
"We are still analysing the results of the extended test, including a structural failure we experienced just before landing," the company's analysis says. "To prove out the full capacity of the design, we will continue to push the plane to its limits under more extreme conditions in a lengthy series of tests."
The NTSB notes that the unmanned aircraft was operating an "experimental test flight".
The agency investigates accidents involving unmanned aircraft with gross takeoff weights of at least 300lb (136kg) that also result in serious injury or substantial aircraft damage, the NTSB says. It expects to release its findings about the incident within two months.
Facebook says a fleet of Aquila UAVs could help bring internet access to some of the 1.6 billion people living in regions without access to mobile broadband networks.
"Once they are fully operational, these high-altitude planes will stay airborne for up to 90 days at a time and beam broadband coverage to a 60-mile-wide area on the ground, helping to open the opportunities of the internet to people in under-connected regions," says the company's 21 July post-flight analysis.
The aircraft does not have a landing gear, but is attached at takeoff from a dolly that is accelerated down the runway, Facebook says.