WESTBURY, NY, USA
N350SL
Eurocopter AS-350-BA
While in cruise flight, the pilot detected a severe vibration and initially elected to return to his departure airport, and then elected to perform a precautionary landing. When the pilot brought the helicopter to a hover, the helicopter rotated nose left. The pilot then landed, shut down the engine, and noticed the tail rotor gear box and vertical fin had separated from the helicopter. One of the tail rotor pitch link control rods was found to have failed. Metallurgical examination of the failed components, found evidence of fatigue on the failed tail rotor pitch link control rod. The manufacturer specified an after last flight of the day (ALF) inspection, as a detailed inspection of the helicopter that could be performed by pilots or maintenance personnel. The Director of Maintenance for the operator reported pilots were responsible for all daily checks. The pilot had not been trained to conduct this inspection, and the FAA check airman who conducted the pilot's initial FAR 135 checkride was not aware of the specifics of the ALF inspection. In addition, the checklist found in the helicopter had not been updated with the latest, more detailed ALF inspection.
On October 27, 1999, at 1538 Eastern Daylight Time, a Eurocopter AS-350-BA, N350SL, was substantially damaged during a precautionary landing in Westbury, New York. The certificated airline transport pilot was not injured. Visual meteorological conditions prevailed for the positioning flight. No flight plan had been filed for the flight that was conducted under 14 CFR Part 91. The pilot reported he had departed from Republic Airport (FRG), Farmingdale, New York, and was en route to the 34th Street Heliport (6N5), New York, New York, at 1,500 feet, when in the vicinity of Westbury, New York, he felt what he described as a, "...sudden, violent, medium frequency vibration that he could feel throughout the entire airframe...." The pilot turned the helicopter around with the intent of returning to FRG. There was no noticeable yaw to the helicopter, and the DOOR light was illuminated. As he slowed the helicopter to approximately 60 knots, the vibration diminished to about 50 percent of its original intensity. En route to FRG, he observed an open field and elected to perform a precautionary landing. He reported he slowed the helicopter to about 40 knots, circled the landing area, and then performed a steep approach with a "normal" rate of descent. After the pilot brought the helicopter to a 3 to 4 feet hover, it suddenly started to rotate nose left. The pilot reported that he recognized this as a lost of tail rotor thrust and immediately lowered the collective. The helicopter had rotated about 270 to 300 degrees when it touched down. The pilot reported that after he shut down the engine and exited the helicopter, he noticed that the tail rotor, with the 90 degree gearbox and vertical stabilizer, had separated from the helicopter behind the horizontal stabilizer. The pilot estimated the flight time from the onset of vibration to the landing was 7 minutes. Examination of the helicopter revealed one of the tail rotor pitch change rods had failed. The failed rod was forwarded to the Safety Board Materials Laboratory for examination. According to the metallurgists factual report: "...The interior surface of the bearing race was severely worn and rubbed. A portion of the bearing race was completely worn away to the retaining rungs across half the width of the race...This level of wear is sufficient to allow the ball...to freely separate from the bearing race...the ball was burnished and scored on most of its surface...Both [fracture] surfaces showed relatively smooth regions with curving boundaries...features typical of fatigue...Fracture surfaces of the tail rotor gearbox output coupling and bolt were examined by optical micropsy. Portions of the surface of the gearbox output coupling were obliterated by post-fracture damage, but the remaining portions had a matte gray appearance characteristic of ductile overstress fracture...The fracture surfaces of the tail boom were examined optically. Except for regions showing post-fracture damage, the fracture surfaces were at an approximately 45 degree angle to the sheet metal plane, features characteristic of an overstress tensile failure of a thin sheet.... Examination of flight and maintenance manuals revealed that Eurocopter specified three types of daily checks; prior to the first flight of the day; in conjunction with a flight; and after the last flight of the day (ALF). These checks as printed in both the flight manual and maintenance manual were identical, and both manuals stated either maintenance personnel or pilots who have been properly trained could perform the checks. The most comprehensive check was the ALF check. The director of maintenance reported that all daily checks including the ALF check were the responsibility of the pilots. In addition, he reported that the helicopter was maintained in accordance with the manufacturer's inspection program. The checklist used by the pilot had been copied from the FAA approved helicopter flight manual, and was current through revision 91-47. An inspector from the Federal Aviation Administration (FAA), Farmingdale, New York, Flight Standards District Office (FSDO) had approved the checklist for use in the helicopter on February 13, 1997. The checklist specified the three daily checks. According to a representative of Eurocopter, the checklist was from the original flight manual with no revisions. The checklist was revised in 1994. The ALF check remained unchanged, but was moved to a different section of the manual. The checklist used by the pilot contained the following information for the ALF check. "...Pitch Change Control" "Pitch change rod swivel bearing...........No play...." In revision 99-17 (17th week of 1999) the checklist was revised again by the manufacturer with a more detailed ALF check specified. The revised checklist stated: "...[check for] the absence of play by twisting the blades back and forth," "The condition of the ball joint by visual inspection," "That no Teflon material has squeezed out," "That the ball shows no signs of burnishing or scoring." By comparison, the check before the first flight of the day specified: "Tail rotor blades....................Condition of skin" "Tail boom and TGB fairings...........Security" In addition, the investigation revealed changes to other areas of the checklist, none of which were posted to the checklist used by the pilots. During telephone interviews, the pilot reported that he had been trained to conduct pre-flight inspections, and to check the helicopter prior to each flight. However, he had not been specifically trained to conduct the ALF check, and was not familiar with the ALF check at the time of the accident. The flight instructor who conducted the pilot's training reported that he reviewed the preflight inspection with the pilot; however, he did not teach the ALF check, as he believed the operators maintenance personnel were conducting daily ALF checks on the helicopter. The FAA inspector who conducted the pilot's initial FAA 135 checkride in the AS-350-BA reported that he was familiar with the specifics of the pre-flight examination of the helicopter. However, he was not familiar with the ALF check as specified in the flight manual at the time of the accident. In follow-up interviews, the FAA inspector reported that when he conducted the pilot's initial FAR 135 pilot-in-command checkride, he observed the pilot conduct what he described as a through pre-flight examination of the helicopter which included checking the tail rotor pitch change control rods. In addition, the FAA inspector reported that 3 months after the accident, he attended recurrent training on the Eurocopter AS-350. The training was conducted by a contractor and was not conducted by Eurocopter. During the training, the ALF inspection was discussed, but not conducted. The emphasis was on a through preflight inspection that was conducted prior to the first flight of the day. A check of Safety Board and Eurocopter records revealed four previous occurrences with similar characteristics. On October 16, 1998, Eurocopter issued Service Letter (SL) 1367-64-98. The SL was subsequently updated on December 1, 1999. The SL specified a hand check of the tail rotor pitch change rod for play in the bearings during the ALF inspection. The check was to be accomplished with the rudder pedals in neutral, and with the tail rotor pitch change rod in place. If any play was detected, then the tail rotor pitch change rod was to be removed for additional checks. On December 17, 1998, the FAA issued airworthiness directive (AD) 98-24-35, for checks on the tail rotor pitch control rod. The AD specified a 50 hour repetitive check by making specified measurements on the tail rotor pitch control rod. If the play exceeded specified limits, the rod was to be changed. The AD did not specify state if the tail rotor pitch control rod was in place or removed at the time of inspection. In addition, the AD did not make reference to the previously issued service letter, or the need to have the rudder pedals in the neutral position when the check was conducted, and the consequences if they are not. The director of maintenance reported that the company did not comply with the SL; however, they did comply with AD 98-24-35.
the failure of the operator to ensure the pilot was adequately trained to conduct all inspections required by the flight manual, which resulted in the pilot's inadequate preflight and subsequent failure of the tail rotor pitch change rod. Factors were the inadequate preflight by the pilot, and the failure of the FAA to detect the deficiency in the pilot's training, and ensure that the operator used the most current checklist available.
Source: NTSB Aviation Accident Database
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