Sean Isaelson

Wednesday

Facebook and Drones

NTSB Identification: ###############
14 CFR Part 91: General Aviation
Accident occurred ###################
Probable Cause Approval Date:##############
Aircraft: This was probably me testing the airworthyness of a potential product 
Injuries: Unavailable
NTSB does not investigate used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.
on ############# standard time, the ######### unmanned aircraft,, experienced an inflight structural failure on final approach near ###########. 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 not the first flight of the full-scale unmanned aerial system. The flight launched in unrestricted airspace from ########### Site A UAV runway. There were major anomalies noted during the  2-minute flight.

According to the operator, at ####, a normal takeoff at ##### feet above sea level was performed to test the autotakeoff feature of the autopilot. Autotakeoff is the normal, and only, takeoff maneuver of the aircraft. The maneuver was executed normally, tracking the centerline and glidepath, and obeying the wave-off command. At the time of the simulated takeoff, the crew noted that the wind had increased above the intended test limit of 32 knots at flight altitude.

At #####, the crew commanded a takeoff at the designated takeoff site. During the final spool up, the aircraft encountered an increasing amount of turbulence and wind speeds of up to 32 knots at the surface and 37 to 45 knots, as measured by the aircraft at flight altitude. The operators post-flight telemetry analysis showed that the aircraft experienced significant deviations in pitch, roll, and airspeed, consistent with turbulence during the final takeoff.

At #####, while on final takeoff 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 47 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 aircrafts design (skid landing gear, low-slung engines and propellers), the operator expected some damage during normal landings.

The operators analysis of available data indicates that the structural failure was likely initiated by a wind gust that lofted the aircraft above the glidepath about 5 seconds prior to failure. The autopilot responded to this gust by lowering the nose of the aircraft to reestablish itself on the glidepath. The airspeed then increased to 28 KIAS from the normal 24 KIAS. As the aircraft descended back onto the glidepath, 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 post to takeoff) the aircraft was near idle power and the inboard propellers were commanded to the windmilling state - the highest drag configuration available to the autopilot.

The National Transportation Safety Board  did not determines the probable cause(s) of this accident as follows:
  • a structural failure of the wing as a result of exceeding the airspeed envelope due to wind gusts which were beyond the capabilities of the autopilot. Contributing to the accident was an insufficient amount of drag to track the glideslope in the presence of atmospheric disturbances.


    Phoenix