ASN Wikibase Occurrence # 217371
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| Date: | Thursday 3 September 2009 |
| Time: | 13:00 |
| Type: |  Robinson R44 Astro |
| Owner/operator: | Universal Air Academy |
| Registration: | N8361X |
| MSN: | 0431 |
| Year of manufacture: | 1998 |
| Total airframe hrs: | 1067 hours |
| Engine model: | Lycoming O-540-F1B5 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Location: | Zamperini Field Airport, Torrance, California -
 United States of America
|
| Phase: | Landing |
| Nature: | Private |
| Departure airport: | Brackett Field, La Verne, California (POC/KPOC) |
| Zamperini Field Airport, Torrance, California (TOA/KTOA) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
On September 3, 2009, about 13:00 PDT (Pacific Daylight Time), a Robinson Helicopter R44, N8361X, was substantially damaged during a practice autorotation at the Zamperini Field Airport (TOA), Torrance, California. (At approximate coordinates 33'80.3333"N, 118'33.9444"W). The helicopter was registered to Business Financial Services Corp., Wilmington, Delaware, and operated by Universal Air Academy, La Verne, California, under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot, sole occupant of the helicopter, was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight. The cross-country flight originated from Brackett Field, La Verne, California (POC) at 12:15 PDT with an intended destination of Torrance.
In a written statement, the pilot reported that he initiated a practice autorotation to the northern helicopter pad from an altitude of 800 feet mean sea level (msl) at an airspeed of 65 knots and rotor RPM of 100 percent. As the helicopter descended through about 100 feet above ground level (agl), the pilot initiated a recovery by “slowly rolling on throttle.” The pilot stated that as the helicopter descended, he noticed the rotor RPM “increase quickly” and that due to the close proximity to the ground, he performed “a landing in the safest manner I could on the helipad.” After landing, the pilot shut the helicopter down normally.
Examination of the helicopter by a Federal Aviation Administration (FAA) inspector revealed that the tail boom of the helicopter was structurally damaged. The tail rotor drive shaft was separated at the forward attach point. The helicopter was transported to a secure location for further examination.
No mechanical anomalies were observed with the engine that would have precluded normal operation.
In a written statement to the NTSB investigator-in-charge, Robinson Helicopter representative reported that within the Robinson Technical Report (RTR) 430, critical shafting speeds for the R44 are described. Four different "whirl modes" are identified along with the critical speeds that are associated with them. Robinson Helicopter stated that the damper bearing assembly is designed to control these vibration modes within the "normal speed operating range" of the tail rotor driveshaft. Testing and analysis within RTR 430 show that the whirl modes are controlled within the normal operating speed range of the R44 and that there is an additional whirl mode frequency that is not damped by the damper bearing assembly. Robinson Helicopter further stated that this whirl mode occurs at approximately 134% rpm and outside of the normal operating speed range of the R44. They also noted that this situation is similar for the R22 model helicopter.
Robinson Helicopter reported that they have seen within two prior occurrences where engine and rotor rpm has been allowed to reach excessively high speeds, damage was observed to multiple bulkheads inside the tailcone, tail rotor drive shaft (including scoring at spacing that correlates with the tailcone bulkheads), damper assembly, tail rotor push pull tube, wiring, and intermediate flex coupling.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A main rotor overspeed due to the pilot’s failure to maintain rotor RPM within allowable limits during a practice autorotation. Robinson R44 N8361X was repaired and returned to service: since the above accident accident, it had been sold on seven times, mostly to owners in Hawaii (see link #4)
Accident investigation:
 |
|
Sources:
NTSB
2. FAA Registration: https://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?omni=Home-N-Number&nNumberTxt=N8361X
3. http://helihub.com/2009/09/03/3-sep-09-n8631x-robinson-r44-torrance-us-california/
4. https://uk.flightaware.com/resources/registration/N8361X
5. http://www.griffin-helicopters.co.uk/accidentdetails.aspx?accidentkey=50576
6. https://planecrashmap.com/plane/ca/N8361X/
7. https://www.regosearch.com/aircraft/photo/us/8361X/11546
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 07-Nov-2018 18:12 | Dr.John Smith | Added |
Corrections or additions? ... Edit this accident description
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