What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
On March 2, 2026, at approximately 13:57 PDT, the subject aircraft (UAS) was conducting an autonomous early-phase research and development test flight at Castle Airport (mer) in Atwater, California.
Approximately one minute and thirty seconds after takeoff, during cruise flight, the aircraft encountered a gust of wind that initiated longitudinal oscillations. The oscillatory behavior demonstrated characteristics consistent with negative dynamic stability. Despite autonomous control inputs, the oscillations progressively increased in amplitude.
The increasing pitch excursions resulted in the aircraft reaching a near-vertical nose-up attitude, which led to an aerodynamic stall. The stall progressed into a right-hand spin while the aircraft descended in an uncontrolled flight path.
The UAS impacted the ground on the north edge of taxiway alpha, just northwest of the taxiway delta intersection. The impact resulted in substantial structural damage and a post-impact fire that consumed approximately 70 percent of the wreckage.
There were no injuries to the remote pilot, support personnel, or bystanders. No ground property damage was reported.
As the FAA filed it
ON MARCH 2, 2026, AT APPROXIMATELY 13:57 PDT, THE SUBJECT AIRCRAFT (UAS) WAS CONDUCTING AN AUTONOMOUS EARLY-PHASE RESEARCH AND DEVELOPMENT TEST FLIGHT AT CASTLE AIRPORT (MER) IN ATWATER, CALIFORNIA.
APPROXIMATELY ONE MINUTE AND THIRTY SECONDS AFTER TAKEOFF, DURING CRUISE FLIGHT, THE AIRCRAFT ENCOUNTERED A GUST OF WIND THAT INITIATED LONGITUDINAL OSCILLATIONS. THE OSCILLATORY BEHAVIOR DEMONSTRATED CHARACTERISTICS CONSISTENT WITH NEGATIVE DYNAMIC STABILITY. DESPITE AUTONOMOUS CONTROL INPUTS, THE OSCILLATIONS PROGRESSIVELY INCREASED IN AMPLITUDE.
THE INCREASING PITCH EXCURSIONS RESULTED IN THE AIRCRAFT REACHING A NEAR-VERTICAL NOSE-UP ATTITUDE, WHICH LED TO AN AERODYNAMIC STALL. THE STALL PROGRESSED INTO A RIGHT-HAND SPIN WHILE THE AIRCRAFT DESCENDED IN AN UNCONTROLLED FLIGHT PATH.
THE UAS IMPACTED THE GROUND ON THE NORTH EDGE OF TAXIWAY ALPHA, JUST NORTHWEST OF THE TAXIWAY DELTA INTERSECTION. THE IMPACT RESULTED IN SUBSTANTIAL STRUCTURAL DAMAGE AND A POST-IMPACT FIRE THAT CONSUMED APPROXIMATELY 70 PERCENT OF THE WRECKAGE.
THERE WERE NO INJURIES TO THE REMOTE PILOT, SUPPORT PERSONNEL, OR BYSTANDERS. NO GROUND PROPERTY DAMAGE WAS REPORTED.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.