Rotorcraft Report: NTSB Urges Tighter Checks on S-76 Actuators

CIVIL

NTSB Urges Tighter Checks on S-76 Actuators

Investigators are reviewing past S-76 accidents for similarities to an Aug. 10, 2005 crash in Estonia in which failure of a main-rotor hydraulic actuator is suspected. All 14 persons on board were killed when the S-76C+ operated by Copterline of Finland pitched up, rolled left, rotated right and plunged into Tallinn Bay. Estonian authorities sent key wreckage to the U.S. NTSB for analysis. Investigators there found the forward main-rotor blade actuator contaminated with flaked-off coating from the hydraulic piston's face. The HR Textron actuator failed a manufacturer's acceptance test and moved uncommanded under certain conditions. Accident flight data is consistent with uncommanded extension of the actuator, according to the NTSB, which urged the FAA to require S-76 operators to immediately inspect main-rotor actuators. More info is at www.ntsb.gov/Recs/letters/2005/A05_33_35.pdf.