ERA21LA390 · Eurocopter AS 350 B3

The pilot reported that he was on a pre-checkride flight and was conducting standard maneuvers as required by the commercial helicopter practical test standards. The flight was uneventful and lasted about an hour. He stated that, during the flight, “we had no hard landings or turbulence;” however, on the postflight checks he immediately noticed buckled metal on the tail boom near the fuselage attachment points. He said he noticed small dents on the bottom and sides of the tail boom when he first flew this helicopter in 2019; however, they were small and were checked pre- and postflight without signs of growth until this flight. An examination and review of the tail boom section by an Airbus representative and NTSB structural engineer noted wrinkled skin damage on the tail boom. Both Airbus and the NTSB agreed that this was very similar to cases in which the tail boom structure has been subjected to loads above the design load. As a result, the tail boom was permanently deformed and the structural strength was compromised, most likely from a hard landing event. The buckling of the lower portion of a semi-monocoque structure such as the tail boom is considered substantial damage since it adversely affects the structural strength and requires major repair or replacement. The exact time and date of the hard landing was not determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset