Redding, CT, USA
N8313E
ROBINSON HELICOPTER COMPANY R22 MARINER
The pilot stated that he felt an abnormal vibration in the helicopter during cruise flight. He performed a precautionary landing to residential driveway. Postincident examination revealed that the tail rotor teeter hinge bolt had fractured completely due to fatigue and that there was no torque stripe on the bolt to help identify possible movement. The manufacturer’s preflight inspection checklist required the pilot to verify that the tail rotor teeter hinge bolt does not rotate. When asked about preflight inspections, the pilot stated that he does not always use the manufacturer's preflight checklist. Maintenance records show that the most recent annual inspection was performed about 4 weeks before the incident. According to the manufacturer's maintenance procedures, during an annual inspection, a mechanic should verify that the tail rotor teeter hinge bolt remains stationary when teetering the hub. Also, it is recommended that a mechanic applies a torque stripe to the bolt. In addition, the maintenance manual contained an unboxed warning message about the importance of the correct installation of the tail rotor to prevent a failure of the teeter hinge bolt and loss of the tail rotor.
On May 29, 2011, at 1508 eastern daylight time, a Robinson R22 Mariner, N8313E, performed a precautionary landing into a driveway near Redding, Connecticut. The certificated private pilot and passenger were not injured. The helicopter was not damaged. The flight was operated under the provision of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, and no flight plan was filed. The flight originated from Kingston-Ulster Airport (20N), Kingston, New York, around 1330, with the intended destination of Brookhaven Airport (HWV), Shirley, New York. The pilot stated he was at approximately 2,700 feet over Danbury Municipal Airport (DXR), Danbury, Connecticut, when he heard a slight noise and felt a vibration in the helicopter. He immediately performed a precautionary landing ,landing in a driveway located near a residence in Redding, Connecticut, approximately 4 miles to the southeast of the airport. The pilot exited the helicopter while it was running in order to determine exactly where the vibration was originating. Upon inspection of the tail rotor section of the helicopter, the pilot heard a "click, click, click" noise. Upon further inspection he discovered that the tail rotor teeter hinge bolt was sheared and exhibited rotational scoring. A post incident inspection of the helicopter by a Federal Aviation Administration (FAA) inspector revealed that one part of the tail rotor teeter hinge bolt could be rotated by hand. Also, photographs taken on the day of the incident revealed that there were no torque stripes on the tail rotor teeter hinge bolt. In a telephone interview, the pilot stated that he received a biennial flight review in August of 2010. While performing the preflight inspection that day, the flight instructor giving the biennial flight review indicated that there was a problem with the tail rotor teeter hinge bolt. The pilot asked two mechanics to examine the bolt to verify that it was in operating condition, and both mechanics stated that the bolt looked normal. The pilot also indicated that when he performed a preflight inspection, he did not usually use a checklist. He keeps the checklist in the helicopter if it is needed for reference, but he checks "all screws for any suspicious items that might affect the flight." In addition, he sometimes cannot determine what parts "should be tight and what should be loose," when checking the components during a preflight inspection. He further stated that when he performed a preflight inspection the day of the incident; everything was "normal." The Robinson R22 Preflight Checklist "Tail Rotor" section stated when checking the teeter bearing bolt verify that it "does not rotate." According to FAA and pilot records, the pilot held a private pilot certificate with a rating for rotorcraft-helicopter. His most recent second class medical was issued on September 30, 2010, and at that time he reported 1,100 of total flight time. The pilot reported that he accumulated 1,000 hours of total flight time, all of which were in the same make and model as the incident helicopter. According to FAA records, the helicopter was manufactured in 1994. According to an FAA inspector, the most recent annual was completed on May 1, 2011 in accordance with the "Robinson R22 service manual checklist," and the helicopter had accumulated approximately 2,200 total flight hours in service at that time. The FAA inspector also stated that the most recent maintenance overhaul of the tail rotor section of the helicopter was about five years prior to the incident. According to the pilot, the tail rotor teeter hinge bolt was replaced about 800 flight hours prior to the incident. According to the Robinson R22 Annual Maintenance Inspection Checklist "Tail Rotor Hub" section, "verify teeter hinge bear balls, spacers contacting output shaft, nuts and bolt, remain stationary when teetering hub." It further stated under the "Fasteners and Torque Stripes" section, "Inspect condition and verify security of all fasteners. Renew deteriorated torque stripes." A review of the Robinson R22 Maintenance Manual "Tail Rotor Installation with Spherical Teeter Bearings" section showed that there was a warning message about the tail rotor teeter hinge bolt that emphasized the importance of correct installation but was not boxed to draw attention. The warning message stated, "Failure to check tail rotor for proper installation per step 5 can result in failure of teeter hinge bolt and loss of tail rotor." Examination of the tail rotor teeter hinge bolt by the NTSB Materials Laboratory revealed that the bolt exhibited corrosion and wear on the bolt shank between the spacers and wear on the opposed end faces of the spacers. Magnified examinations of the fracture revealed fracture traces and arrest lines consistent with fatigue progression through approximately half of the shank diameter of the bolt. For further information about the examination a detailed report is located in the NTSB docket for this accident.
The pilot's inadequate helicopter preflight inspection and the mechanic’s inadequate annual inspection, both of which failed to detect a worn bolt in the tail rotor teeter hinge prior to its fracture due to fatigue.
Source: NTSB Aviation Accident Database
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