A Boeing CV2 Cargo Air Vehicle was substantially damaged last year when it made a contingency landing in crosswinds that were higher than expected, according to a newly released report from the National Transportation Safety Board (NTSB).
According to the report, the accident occurred during flight testing on the morning of June 21, 2019, at Chase Industrial Airport in Beeville, Texas (north of Corpus Christi). At that point, flight testing of the large unmanned aircraft system had been going on for several weeks, with approximately 45 flights completed — each of those lasting just four minutes or less.
Boeing told the NTSB that the accident flight was a planned 30-knot flight over the grass area between the runway and the taxiway. Like previous flights of the Cargo Air Vehicle, it was preprogrammed, with the pilot and ground control station operator able to affect the flight only through contingency commands including “abort to planned zone,” “land now,” and “cut power.” The flight test area included a two-level geo-fence boundary to keep the aircraft contained within a safe area; these geo-fences could also trigger contingency actions.
After taking off and turning on course to parallel the runway and taxiway, the aircraft started to deviate laterally from the programmed flight profile, the report states. The aircraft identified the deviation and autonomously triggered an “abort to planned zone” command to land on the taxiway, yet continued to drift.
Upon reaching the first geo-fence boundary, the aircraft autonomously executed a “land now” command. According to the report: “The aircraft appeared to adjust pitch attitude for the abort to planned zone landing and drifted towards the second geo-fence boundary. Upon reaching the outer geo-fence, the aircraft autonomously cut power to all motors and dropped to the ground, as designed.”
The Cargo Air Vehicle, which weighed 933 pounds (423 kilograms) at the time of the accident, was substantially damaged in the crash, with Boeing reporting that the landing gear collapsed, one outrigger broke off the aircraft, and several propellers were damaged. However, the debris field was very small and contained within less than 20 feet (six meters) of the aircraft, and no damage to other property occurred, Boeing said.
After reviewing the flight data, Boeing determined that the lateral deviation initiated due to higher than expected and accounted for wind. Although winds at the accident location were reported to be just 10 knots with six-knot gusts, they were sufficient to result in high vibration within the aircraft navigation system. The contingency logic was unable to return the aircraft to the planned abort zone prior to reaching the outer geo-fence.
Boeing further concluded that there had been insufficient tests related to high crosswinds, insufficient ability to determine winds during test flights, and inadequate physical separation between the abort to planned zone and geo-fence locations, the report states.
A Boeing spokesperson told eVTOL.com, “Safety is always our number one priority. The Cargo Air Vehicle’s safety contingency system functioned as designed when it activated during the flight. The outcome of every flight test allows us to expand our knowledge and apply lessons learned to continually enhance the safety and reliability of our products.”
The Cargo Air Vehicle accident occurred less than three weeks after the June 4 crash of an unmanned Passenger Air Vehicle prototype developed by Boeing subsidiary Aurora Flight Sciences. In that accident during flight testing in Manassas, Virginia, the aircraft fell from the air after resonant aircraft vibrations incorrectly activated its ground mode, commanding its motors to shut down, according to an earlier NTSB report.
This story has been updated with comment from Boeing.