Shirley, NY, USA
N3666J
CESSNA 150G
The student pilot and flight instructor were en route to the airport, with the airplane cruising at 4,500 ft above mean sea level, when the student noticed a roughness and vibration coming through the control wheel. He told the flight instructor about it and then noticed that the left elevator tip was hanging down 6-10 inches from its normal mounting position. The flight instructor took control of the airplane and noticed that the left elevator was moving up and down uncontrollably. The flight instructor made a 7-mile-long, straight-in approach to the runway, where the airplane touched down firmly without further incident. Examination of the elevator and horizontal stabilizer revealed that the airplane’s elevator was substantially damaged. The left side of the elevator was bent downward, and the left outboard elevator attachment bolt had backed out of the nutplate. In addition, the right elevator attachment bolt would move in the nutplate when the elevator was moved up or down. With the outboard left side of the elevator no longer attached to the horizontal stabilizer, it is likely that the air loads imparted onto the partially supported elevator during the flight bent it and resulted in the reduced pitch controllability. Further examination of the attachment bolts from both the left and right side of the elevator revealed that both displayed signs of thread wear on the end of the bolt that would have been fully engaged with the nutplate. Both nutplates displayed corrosion outside the threaded area on the backside of each nutplate, and the nutplate from the left side would not hold specified torque and displayed evidence of cross-threading, which may have occurred either before or during replacement of the bolts about 6 years earlier. Review of maintenance records indicated that two new bushings and elevator attachment bolts had been installed about 6 years before the accident, but the records did not reflect if the hinge parts were replaced at that time. Review of the airplane manufacturer’s service manuals revealed that supplemental inspection guidance had been issued for inspection of the horizontal stabilizer, elevator, and attachments for signs of damage, fatigue, or deterioration. The airplane had undergone an annual inspection about 6 months before the accident. It is likely that the damage and deterioration of the elevator’s left bolt and nutplate should have been evident during the most recent annual inspection, as well as previous inspections. Review of the Federal Aviation Administration (FAA) Service Difficulty Reporting program database revealed that since 1979, seven other reports of the elevator hinge attachment bolt backing out had been submitted. According to the FAA, the main issues identified included excessively worn attachment hardware and the use of incorrect attachment hardware, with corrosion possibly a contributing factor. As a result, in May 2017, the FAA issued a special airworthiness information bulletin to alert owners, operators, maintenance technicians, and inspectors of the potential for loose bolts at the elevator attachment points on certain models of the airplane type and recommended performing the supplemental inspections detailed in the airplane manufacturer’s service manuals.
On August 13, 2016, about 1300 eastern daylight time, a Cessna 150G airplane, N3666J, was substantially damaged when it was involved in an accident near Shirley, New York. The flight instructor and student pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight departed Montauk Airport (MTP), Montauk, New York, destined for Brookhaven Airport (HWV), Shirley, New York. According to the student pilot, when he and the flight instructor were en route to HWV with the airplane cruising at 4,500 ft above mean sea level, he noticed a roughness and vibration coming through the control wheel. He told the flight instructor about it and then looked outside and noticed that the left elevator tip was hanging down 6-10 inches from its normal mounting position. According to the flight instructor, when the student pilot stated that the airplane was handling “funny,” he took control of the airplane and noticed that the left elevator was moving up and down uncontrollably. At that point, the airplane was directly in line with runway 24 at HWV, so the flight instructor made a slight power reduction to descend at 150 ft per minute; kept the wing flaps retracted; did not move the flight controls; and made a 7-mile-long, straight-in approach to the runway, where the airplane touched down firmly without further incident. Examination of the elevator and horizontal stabilizer revealed that the airplane’s elevator was substantially damaged. It’s left side was bent downward, and the left outboard elevator attachment bolt had backed out of the nutplate. In addition, the right elevator attachment bolt would move in the nutplate when the elevator was moved up or down. Review of the Illustrated Parts Catalog for the airplane make/model indicated that the parts that had separated were the left elevator hinge attachment bolt (P/N AN3-7A) and its self-locking nutplate (P/N NAS682A3). On September 22, 2016, the bolts and nutplates from both the left and right side of the elevator were examined at Textron Aviation’s Materials and Processes Laboratory under supervision of the Federal Aviation Administration. Both of the AN3-7A bolts displayed signs of thread wear, predominantly on the end of the bolt that would be fully engaged with the nut plate. Both nutplates also displayed corrosion outside the threaded area on the backside of each nutplate, and the nutplate from the left side displayed evidence of cross-threading and would not meet the specified torque parameters listed in MIL-N-25027. According to the airplane’s maintenance records, on March 23, 2010, at 2,645.21 total hours of operation, two new bushings and elevator hinge attachment bolts were installed, but the records did not reflect if any other hinge parts were replaced at the same time. At the airplane's most recent annual inspection on February 1, 2016, the airplane had accrued about 2,860 total hours of operation. Review of the Cessna Model 100 series (1963 through 1968) and Cessna Model 150 series (1969 through 1976) service manuals revealed that supplemental inspection guidance (supplemental inspection number 55-10-01) had previously been issued for inspection of the horizontal stabilizer, elevator, and attachments for signs of damage, fatigue, or deterioration. The supplemental inspection requirements for Cessna Model 100 series airplanes indicated initial inspection compliance of 5,000 hours or 20 years and repeat inspection compliance of 2,000 hours or 4 years. The supplemental inspection requirements for Cessna 150 series airplanes indicated initial inspection compliance of 10,000 hours or 20 years and repeat inspection compliance of 2,000 hours or 4 years. Time limits for the initial inspections were set by either flight hours or calendar time, whichever occurred first. Corresponding calendar inspection times were per repeat flight hour or calendar time specified, whichever occurred first. On May 11, 2017, the FAA issued Special Airworthiness Information Bulletin (SAIB) CE-17-12 to alert owners, operators, maintenance technicians, and inspectors of the potential for loose bolts at the elevator attach points on certain Textron Aviation Inc. (Cessna Aircraft Company) 150 and 152 model airplanes. The SAIB noted that review of the FAA Service Difficulty Reporting program database revealed that since 1979, seven other reports of elevator hinge attachment bolts backing out had been submitted. According to the FAA, the main issues identified included excessively worn attachment hardware and the use of incorrect attachment hardware, with corrosion possibly a contributing factor. As part of the SAIB, the FAA recommended performing the inspections detailed in Cessna supplemental inspection number 55-10-01.
Maintenance personnel’s inadequate maintenance and inspection of the airplane, which resulted in the left elevator attachment bolt backing out of the nutplate, and partial inflight separation and damage of the elevator.
Source: NTSB Aviation Accident Database
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