FA33N7WLTR

On February 20, 2024, at 1438 eastern standard time, an Apellix B1 small unmanned aircraft system (sUAS), FA33N7WLTR, was involved in an accident near Orlando, Florida. The remote pilot-in-command (RPIC) was seriously injured. The flight was operated under the provisions of Title 14 Code of Federal Regulations Part 107.

According to the RPIC, the purpose of the flight was to perform a power wash cleaning of a hospital; the accident flight occurred on the second day of cleaning. The RPIC stated that the sUAS operated normally throughout the day without any signs of control issues. During a repositioning flight, the RPIC reported that after taking off, and at an altitude of about 3 feet above the takeoff point, the sUAS began to lose directional control. The RPIC attempted to control the sUAS using the normal controls from the remote control; however, it responded erratically to any inputs the RPIC commanded through the control station. The RPIC attempted to disarm the motors with the control station; however, the RPIC reported that the sUAS did not respond to the command to disarm the motors. The RPIC determined that he no longer had control over the sUAS and decided to grab the sUAS and unplug the battery manually to disarm it. While unplugging the battery, the RPIC sustained several lacerations on his arms, hands, and legs, and partially severed one of his fingers. A review of the onboard GPS location data and aerial imagery revealed the accident flight was on top of a hospital roof. The flight track revealed that it was operating near a large rectangular object that is consistent with a commercial air conditioning unit.

The RPIC was asked about the training he received for operating the sUAS. The RPIC reported that because he already had experience operating other power washing sUASs he received condensed training provided by the manufacturer. The RPIC also stated that during the training he asked the representative how to shut off the motors in case of an emergency and was told that bringing both control sticks down and inward should shut down the motors in an emergency.

The manufacturer’s operations manual, Section 2.4 “Fly-Away (Complete Loss of Control),” stated that the RPIC should first attempt to send the return to home command to the sUAS; next, the RPIC should activate the flight termination system (if equipped). If these steps failed, the RPIC was to note the direction of travel, maintain visual line of sight with the sUAS, and warn others who were near it. Further review of the sUAS operations and wash system user manuals revealed no instructions on how to disarm the sUAS in an emergency or how to engage the flight termination system. According to the manufacturer, the accident sUAS was configured to shut down by the RPIC bringing both sticks inward at a 45-degree angle (the same command used to start the motors). The manufacturer reported that the system worked by shutting down all power, including power to the motors and the flight processor.

Before notifying the NTSB of the accident, the operator returned the sUAS to the manufacturer for repair. The manufacturer downloaded the flight controller’s internal datalogger, repaired the sUAS, and returned the sUAS to the operator. The sUAS was also not provided to an inspector from the FAA before the repairs. According to Apellix, the sUAS was repaired and returned to service by replacing the following components: all the propellers, two arms with their respective electrical motors, the radio, the receiver, and the lower parts of the landing gear.

The downloaded data from the flight controller’s internal datalogger was provided to the NTSB by the manufacturer. A review of the data of the accident flight revealed that the sUAS was airborne for approximately 19 seconds and was locked on to 14 GPS satellites when it became airborne using the assisted takeoff mode at 1437:58. The sUAS was then switched to the GPS Positioning mode (P-GPS). For the next 5 seconds, the data revealed the remote controller (RC) commanded a positive elevator change of 100%; however, the pitch in degrees remained relatively unchanged. Around the same time, the RC commanded a positive aileron (roll) input to 100%; the roll angle increased to a +9.9°. The elevator was then commanded back to 0% followed by an immediate increase back to a +100%; the pitch then changed to a -10.1° (Note: It is normal for a positive elevator input of the RC to create a negative pitch angle of the sUAS). During this time, the rudder command (yaw) was set to a maximum of -50%; the sUAS responded with a compass heading change from 124.7° to 84.9°. There were no alerts noted in the fault log that would indicate a problem during the first 5 seconds of flight.

From 1438:03 through 1438:07, the elevator command decreased to 0% followed by an immediate increase to +100%; the pitch changed to -9.7°. The elevator control then changed back to 0% and the pitch varied between -15.4° and +5.1°. During this time the aileron input varied between -65% and 100%; however, the sUAS roll did not fully correspond with the input. At 1438:04, the aileron input was set to +100% and the roll amount was reported to be +13.1°; when the aileron input moved to a lower level of +32%, the sUAS reported a roll level of +47.1°. During this same time period, the rudder input remained at 0%; however, the sUAS compass heading indicated a left turn from 58.4° to 16.9°, followed by a right turn to 79.9°, and then another left turn to 54.7°. One second later, the log reported a fault “fault on, magn_heading_err_large,” indicating a fault noted with the magnetometer. After the fault occurred, the sUAS was switched to “Sport” mode. After another second, the fault “COMPASS(2): fault on, over_large” was reported. The fault then turned off and back on two more times within 1 second of the recording. Shortly after recording the first fault, the number of GPS satellites that were locked decreased from 12 to 5.

From 1438:08 through 1438:10, the elevator control remained mostly at 0% with the only significant increase up to +54% for less than 1 second. The sUAS’s pitch at this time varied between -9.2° to a +20.4°. The aileron input varied between +23% and +100% and the sUAS’s varied between .5° and 29.3°. The rudder input remained at 0% during this time period; however, the compass heading indicated a constant right turn from 55.4° to 183.1°. The data also logged another “COMPASS(2): fault on, over_large” error as well as a fault indicating “COMPASS(2): fault on, interfere.” During this time the GPS satellite locks increased from 5 to 11.

The last 6 seconds of data revealed the elevator input was set to -100%; however, the sUAS’s pitch remained relatively stable at approximately +2°. The aileron input remained stable at 2%; however, the sUAS’s roll was reported to be about +65°. The rudder control was increased to +65%; however, the compass heading remained relatively stable around 164°. During the 35th second of the recording, the data log indicated two new faults, “[CTRL]: fault on , height_ctrl_fail” and “[L-RC]craft ctrl failed!!!.” The recording then ended with the elevator input at -100%, sUAS pitch angle at +1.6°, aileron input at +2%, sUAS roll angle at +64.1°, rudder input at +65%, and a compass heading of 164.7°.

Further examination of the control stick inputs in the recorded data revealed that the control sticks were not moved into the disarm position during the accident flight. The data revealed that throughout the time the sUAS was airborne, the sUAS reported that it was connected to the RC and there were no alerts indicating a lost link. According to the manufacturer, none of the recorded magnetometer errors would have been provided as feedback to the RPIC.