History of Flight
On January 17, 2013, about 1245 eastern standard time, a Robinson R-22 Beta helicopter, registration N26NE, was substantially damaged following a loss of control during a practice autorotation at Ellington Airport (7B9) in 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, which originated from 7B9 about 1240. The flight was conducted under Title 14 Code of Federal Regulations Part 91.
According to the CFI, the helicopter remained at traffic pattern altitude to conduct a practice autorotation. After turning onto the final leg of the traffic pattern, 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 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, resulting 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 FAA second-class medical certificate was issued March 30, 2012. The pilot reported 1,326 total flight hours, of which 1,033 were in the accident helicopter make and model.
The pilot receiving instruction held a commercial pilot certificate with ratings for rotorcraft-helicopter and instrument helicopter. His most recent FAA second-class medical certificate was issued September 22, 2011. He reported 196 total flight hours, 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 accident date. 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 on June 6, 2011. Examination of maintenance records showed that the overhaul was initiated on December 2, 2010. The operator stated that he, along with licensed and unlicensed mechanics, worked on the helicopter under his supervision during the six 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 degrees at 6 knots. The temperature was 4°C, the dew point was -2°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, so the original as-found condition could not be determined. Examination revealed no exposed bare metal in the hole of the jackshaft arm, and no evidence of damage to the locknut or the bolt threads. Circumferentially oriented smearing and scratches were observed on the washer side of the bolt head, on the safety washer on the bolt head side, and on the spacer side of the safety washer. The spacer displayed circumferential smearing and scratches matching the end diameter of the ball in the rod end. One side of the washer showed a ring of circumferential smearing and scratches matching the other end of the tubular portion of the jackshaft; the locknut side of the washer matched the contact face of the locknut.
The bolt had lost most of its electroplated coating and exhibited features consistent with fretting wear scars. The bolt threads were relatively undamaged but had some small crest deformations. The interior surface of the jackshaft bolt hole, examined via longitudinal cross-section, showed 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.