# NTSB CHI03IA033: Hughes OH-6, N353RK, Moberly, MO, December 5, 2002 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: December 5, 2002, 09:00 local (15:00 UTC) - Place: Moberly, MO - Coordinates: 39.46389, -92.427497 - Nearby events: https://openairdocs.org/map.md?lat=39.4639&lon=-92.4275&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 28, 2004 - Report: Approved by Office Director - Parties: FAA-St. Louis FSDO - NTSB case key (mKey): 56189 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI03IA033 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/56189/pdf - Page: https://openairdocs.org/ntsb/CHI03IA033 ## Probable cause The loss of tail rotor effectiveness during cruise flight due to the bellcrank pivot pin becoming separated from the non-rotational swashplate. The plain brass liner of the non-rotating swashplate and the bellcrank pivot pin were worn. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - rotor system,tail rotor hub pitch change mechanism - failure,total (cause) - rotor system,tail rotor hub pitch change mechanism - worn (cause) ## Analysis The helicopter lost tail rotor effectiveness during cruise flight, and the pilot executed a run on landing to a paved runway. The pilot reported that he was in cruise flight for approximately one hour when the helicopter "entered an estimated 20 degree uncommanded yaw to the right." Applying pressure to the anti-torque pedals had no effect. The pilot reported that there had been no advance auditory indications or unusual vibrations prior to the yaw occurring. The pilot flew to an airport about 12 nautical miles away, and executed a successful run on landing. The inspection of the helicopter revealed that the tail rotor bellcrank pivot pin was dislodged from the non-rotating swashplate and was rotated inboard towards the boom. The plain brass liner, which is a pressed liner internal to the non-rotating swashplate and surrounds the tail rotor gearbox output shaft, was broken into 15 identifiable pieces. No evidence of fatigue or abnormal wear was found on the pieces of the plain liner. The splined brass liner within the non-rotating swashplate was damaged. Eight of the seventeen splines of the swashplate splined liner had fractured areas and one of the splines was cracked. No evidence of fatigue was found on any of the fractures. The splined liner was still riveted to the rotating swashplate and was still capable of bearing a load. The tail rotor gearbox was replaced with an overhauled gearbox 29.4 flight hours prior to the time of the incident. There was no record of any mechanical discrepancies to the tail rotor assembly, including the non-rotating swashplate, when the overhauled tail rotor gearbox was installed. ## Factual narrative On December 5, 2002, at 0900 central standard time, a Hughes OH-6, N353RK, operated by Freelance Air, Inc., lost tail rotor effectiveness during cruise flight and executed a run on landing at the Omar N Bradley Airport (MBY), Moberly, Missouri. The helicopter was not damaged and the pilot was not injured. The 14 CFR Part 91 repositioning flight departed the Spirit of St. Louis Airport (SUS), St. Louis, Missouri, at 0810, en route to Trenton, Missouri. Visual meteorological conditions prevailed. No flight plan was filed. The pilot reported that he was in cruise flight for approximately one hour when the helicopter "entered an estimated 20 degree uncommanded yaw to the right." Applying pressure to the anti-torque pedals had no effect. The pilot reported that there had been no advance auditory indications or unusual vibrations prior to the yaw occurring. The pilot reported he applied left cyclic and maintained airspeed. He flew to MBY, which was about 12 nautical miles away. Once he arrived at MBY, he executed a successful run on landing to runway 31. The inspection of the helicopter revealed that the tail rotor bellcrank pivot pin was dislodged from the non-rotating swashplate and was rotated inboard towards the boom. The non-rotating swashplate spherical bearing boss was found damaged and there appeared to be fine ferrous material around the bellcrank area. The non-rotating swashplate had abnormal play around the tail rotor gearbox output shaft. Excess vertical play was found in the bellcrank arm at the bellcrank attachment bolt. The tailrotor gearbox and the non-rotating swashplate assembly were sent to Boeing Product Integrity, Mesa, Arizona, for further inspection and teardown. The inspection revealed the following: 1. The plain brass liner, which is a pressed liner internal to the non-rotating swashplate and surrounds the tail rotor gearbox output shaft, was broken into 15 identifiable pieces. No evidence of fatigue or abnormal wear was found on the pieces of the plain liner. 2. The splined brass liner within the non-rotating swashplate was damaged. Eight of the seventeen splines of the swashplate splined liner had fractured areas and one of the splines was cracked. No evidence of fatigue was found on any of the fractures. The splined liner was still riveted to the rotating swashplate and was still capable of bearing a load. 3. The bellcrank assembly was undamaged, however, both bellcrank bolt holes showed evidence of distortion or elongation. 4. After the removal of the outer boot, swashplate assembly and the bellcrank from the tail rotor drive shaft, both the tail rotor gearbox output shaft and in input shaft rotated freely without binding. (See Boeing Engineering Laboratory Report, 03L0312, included in the docket) Maintenance records indicated that the last 100 hour inspection occurred on April 25, 2002, at 3,700.3 hours aircraft total time. The total time on the aircraft at the time of the accident was 3,781.1 hours. The non-rotational swashplate was installed as an overhauled unit on November 23, 1999. The swashplate had 385.4 flight hours since the time of overhaul. The tail rotor gearbox was replaced with an overhauled gearbox on October 25, 2002. The helicopter had a total time of 3,760.8 hours. The tail rotor gearbox had 29.4 flight hours since overhaul at the time of the incident. There was no record of any mechanical discrepancies to the tail rotor assembly, including the non-rotating swashplate, when the overhauled tail rotor gearbox was installed. ## Aircraft - Registration: [N353RK](https://openairdocs.org/deregistered/N353RK-2013-05-30), registration cancelled 2013-05-30, S/N 701435 (OpenAirDocs) - Reported make and model: Hughes OH-6 - Registry model: [Hughes 369A](https://openairdocs.org/model/hughes-369a) (registry code 4470503) (OpenAirDocs) - Category: Helicopter - Serial number: 701435 - Airframe hours: 3791 - Engines: Allison 250-C20C 420 lbs thrust turbo shaft - Damage: Minor damage - Flight: Ferry, Public use - Operator: Freelance Air Inc. - Registered owner: U.S. Drug Enforcement Agency - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Continuous airworthiness, December 3, 2002, 1.8 hours before - Departed: SUS, St. Louis, MO - Destination: Omaha, NE - Airport: MBY, Omar N Bradley Airport, runway 31, 4,681 × 100 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 40; injuries: none; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane, helicopter; medical: class 2, with waivers/limitations; last flight review July 31, 2002; seat: right; flight hours: 2,230 total, 237 in this make and model, 1,920 as pilot in command, 128 in the last 90 days, 25 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 330° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 27 °F, dew point 19 °F - Altimeter: 30.34 inHg - Observed at: SUS, 130 nm away From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.