Ellington, CT, USA
N26NE
ROBINSON HELICOPTER R22 BETA
According to the flight instructor, the helicopter remained at traffic pattern altitude in order to conduct a practice autorotation. As the helicopter turned onto the final leg of the traffic pattern, the instructor and the pilot receiving instruction initiated an autorotation from about 950 feet above ground level by lowering the collective and reducing the throttle. Upon entry, the pilots observed an "excessively high" rotor rpm indication that continued to climb toward the top of the tachometer. Both pilots raised the collective control and pushed the cyclic control forward to decrease the rotor rpm, but the rotor rpm remained high and did not respond to control inputs. As the helicopter approached the runway, the instructor elected to terminate the autorotation with power and instructed the pilot to "join" the needles on the dual tachometer by restoring full engine power. Both the instructor and the pilot applied engine power simultaneously; however, the engine tachometer indicated an overspeed condition. The instructor assumed sole control of the helicopter and initiated a deceleration, but the helicopter pitched up, rolled right, and impacted the ground on its side, resulting in substantial damage to the main rotor and fuselage. Examination of the wreckage revealed that the vertical collective control push-pull tube was disconnected from the collective jackshaft assembly. A search of the wreckage resulted in the recovery of the attachment bolt and its associated washers and locknut, but the locking device was not found. Examination of the bolt and locknut threads revealed that they were undamaged. The bolt, locknut, washers, spacers, and the interior bore of the collective jackshaft assembly exhibited radial and axial smearing and fretting wear scarring of their contact surfaces. The wear was consistent with a lack of tightening force on the attachment hardware at installation. The helicopter's most recent overhaul was completed about 2 years before the accident, and subsequent inspections were performed between the time of the overhaul and the accident. The operator stated that he, along with licensed and unlicensed mechanics who he supervised, worked on the helicopter during the 6 months required for completion of the overhaul.
HISTORY OF FLIGHTOn January 17, 2013, about 1245 eastern standard time, a Robinson R-22 Beta helicopter, N26NE, was substantially damaged following a loss of control during a practice autorotation at Ellington Airport (7B9), Ellington, Connecticut. The flight instructor (CFI) sustained minor injuries and the commercial-rated pilot receiving instruction was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight that originated from 7B9 about 1240, and was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. According to the CFI, the helicopter remained at traffic pattern altitude in order to conduct a practice autorotation. The helicopter turned onto the final leg of the traffic pattern and the CFI and the pilot initiated a practice autorotation from about 950 feet above ground level by lowering the collective and reducing the throttle. Upon entry, the pilots observed an "excessively high" rotor RPM indication that continued to climb toward the top of the tachometer. Both pilots raised the collective control and pushed the cyclic control forward to decrease the rotor RPM, but the rotor RPM remained high and did not respond to control inputs. As the helicopter approached the runway, the CFI elected to terminate the approach with power, and instructed the pilot to "join" the needles on the dual tachometer by restoring full engine power. Both the CFI and the pilot applied engine power simultaneously; however, the engine tachometer also indicated an overspeed condition. The CFI assumed sole control of the helicopter and initiated a deceleration, but the helicopter pitched up, rolled right, and impacted the ground on its side, which resulted in substantial damage to the main rotor and fuselage. PERSONNEL INFORMATION The CFI held a commercial pilot certificate with ratings for rotorcraft-helicopter and instrument helicopter. He also held a flight instructor certificate with ratings for rotorcraft-helicopter and instrument helicopter. His most recent Federal Aviation Administration (FAA) second class medical certificate was issued March 30, 2012. The pilot reported 1,326 total hours of flight experience, of which 1,033 were in the accident helicopter make and model. The pilot held a commercial pilot certificate with ratings for rotorcraft-helicopter and instrument helicopter. Prior to the accident, his most recent FAA second class medical certificate was issued September 22, 2011. The pilot reported 196 total hours of flight experience, of which 170 were in the accident helicopter make and model. AIRCRAFT INFORMATION According to operator records, the helicopter was manufactured in 1993 and had accrued 11,974 total aircraft hours as of the date of the accident. Its most recent annual inspection was completed June 19, 2012 and the most recent 100 hour inspection was completed January 8, 2013. The helicopter's most recent overhaul was completed by the operator June 6, 2011. Examination of maintenance records revealed that the overhaul was initiated December 2, 2010. When asked who participated in the overhaul, the operator stated that he, along with licensed and unlicensed mechanics worked on the helicopter under his supervision over the 6 months the helicopter was in overhaul. METEOROLOGICAL INFORMATION At 1251, the weather reported at Bradley International Airport (BDL), located 10 miles northwest of the accident site, included a broken ceiling at 3,700 feet, 10 miles visibility, and wind from 290 at 6 knots. The temperature was 4 degrees C, the dew point was minus 2 degrees C, and the altimeter setting was 30.00 inches of mercury. WRECKAGE AND IMPACT INFORMATION Examination of the wreckage by FAA inspectors revealed that the vertical collective control push-pull tube was disconnected from the collective jackshaft assembly. A search of the wreckage resulted in the recovery of the attachment bolt, its associated washers and locknut, but the locking device (palnut) was not found. The recovered items were submitted to the NTSB materials laboratory for further examination. TESTS AND RESEARCH On March 4, 2014, the attachment hardware components were examined in the NTSB Materials Laboratory in Washington, D.C. As referenced in the Robinson Illustrated Parts Catalogue (IPC), they included the attachment bolt (IPC part no. 28), washer (no. 18), spacer (no. 20), washer (no. 25), nut (no. 13), rod end bearing (no. 3), nut (no. 5), and the collective jackshaft assembly (no. 26). The bolt assembly arrived at the NTSB lab fully assembled, and as such, the original as-found condition of the hardware could not be determined. The NTSB examination of the hardware revealed no exposed bare metal in the hole of the jackshaft arm. There was also no evidence of damage to the locknut or the bolt threads. Examination of the hardware revealed circumferentially oriented smearing and scratches on the washer side of the bolt head. A ring of circumferential smearing and scratches were observed on the safety washer on the bolt head side. The spacer side of the safety washer displayed a ring of circumferential smearing and scratches that matched the ring of smearing and scratches on the spacer. The other side of the spacer displayed circumferential smearing and scratches that matched the end diameter of the ball in the rod end. One side of the washer displayed a ring of circumferential smearing and scratches that matched the other end of the tubular portion of the jackshaft. The locknut side of the washer displayed a ring of circumferential smearing and scratches that matched the contact face of the locknut. Examination of the bolt revealed it had lost most of its electroplated coating and exhibited features consistent with fretting wear scars. The thread on the bolt was relatively undamaged, but exhibited some small crest deformations. To examine the interior surface of the jack shaft bolt hole, the bolt hole was longitudinally cross-sectioned, and the exposed interior surfaces illustrated the presence of fretting wear scars. The contact faces of the locknut and washer displayed circumferentially oriented smearing and scratches. Examination of the rod-end revealed no mechanical damage and negligible play in the bearing.
The separation of the collective push-pull tube and jackshaft assembly, which resulted in the total loss of helicopter control and collision with terrain. Contributing to the accident was the inadequate supervision of maintenance personnel by the operator during overhaul, which resulted in inadequate tightening force applied to the collective jackshaft attachment hardware, and the failure of maintenance personnel to detect the loose hardware during subsequent inspections.
Source: NTSB Aviation Accident Database
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