Facebook Aquila accident report NTSB full narrative

Released into the wild, what the NTSB believed happened. An in-flight breakup due to the platform being operated outside of weather limits.

It was a test flight so incidents and accidents are to be expected really and of course the beauty of unmanned systems is that nobody was hurt.

A very impressive machine from Facebook despite the hiccup.

“On June 28, 2016, at 0743 standard mountain time, the Facebook Aquila unmanned aircraft, N565AQ, experienced an in-flight structural failure on final approach near Yuma, Arizona. The aircraft was substantially damaged. There were no injuries and no ground damage. The flight was conducted under 14 Code of Federal Regulations Part 91 as a test flight; the aircraft did not hold an FAA certificate of airworthiness.

This was the first flight of the full-scale aircraft. The flight launched in restricted airspace from Yuma Proving Ground’s (YPG) Site 8 UAV runway. There were no anomalies noted during the 90-minute flight.

https://youtu.be/eOez_Hk80TI

According to the operator, at 0704, a simulated landing at 1,250 feet above sea level was performed to test the autoland feature of the autopilot. Autoland is the normal, and only, landing manoeuvre of the aircraft. The manoeuvre was normally executed, tracking the centerline and glide path, and obeying the wave-off command. At the time of the simulated landing, the crew noted that the wind had increased above the intended test limit of 7 knots at flight altitude.

At 0737, the crew commanded a landing to the designated landing site. During the final approach, the aircraft encountered an increasing amount of turbulence and wind speeds of up to 10 knots at the surface and 12 to 18 knots, as measured by the aircraft at flight altitude. The operator’s post-flight telemetry analysis showed that the aircraft experienced significant deviations in pitch, roll, and airspeed, consistent with turbulence during the final approach.

At 0743, while on final approach at 20 feet above the ground, the right outboard wing experienced a structural failure with a downward deflection. Four seconds later, the aircraft impacted the ground at a groundspeed of 25 knots in an approximately wings-level attitude. The aircraft sustained substantial damage as a result of the impact and wing failure. As a result of the aircraft’s design (skid landing gear, low-slung engines and propellers), the operator expected some damage during normal landings.

The operator’s analysis of available data indicates that the structural failure was likely initiated by a wind gust that lofted the aircraft above the glide path about 5 seconds before failure. The autopilot responded to this gust by lowering the nose of the aircraft to reestablish itself on the glide path. The airspeed then increased to 28 KIAS from the normal 24 KIAS. As the aircraft descended back onto the glide path, the autopilot started to deflect the elevons upwards.

The operator determined that the combination of high airspeed, up elevon, and low angle of attack, resulted in increased downward lift (and torsion) on the outer wing panels. This loading exceeded its structural limit and resulted in a downward deformation and failure of the right wing. At the time of the last gust (5 seconds prior to touchdown), the aircraft was near idle power and the inboard propellers were commanded to the windmilling state – the highest drag configuration available to the autopilot.”