Primary finding
Probable cause
The incorrect altitude indication by test software during landing.
Investigator assessment
Analysis narrative
The operator of the unmanned aircraft system (UAS) reported that, during a test flight with a new software upgrade, the UAS completed the delivery mission and was transitioning to land, when all six motors suddenly stopped. The UAS fell to the ground and impacted the asphalt taxiway, resulting in substantial damage to the fuselage. Examination of the UAS by the operator revealed that the newly installed software caused an incorrect altitude reading in the UAS during landing, causing the motors to shut down. The operator reported that there were no preaccident mechanical failures or malfunctions with the UAS that would have precluded normal operation.