# NTSB LAX00TA163: Hughes OH-6A, N61869, Green Valley, AZ, April 20, 2000 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Final report - Date: April 20, 2000, 07:15 local (14:15 UTC) - Place: Green Valley, AZ - Coordinates: 31.809152, -110.91957 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=31.8092&lon=-110.9196&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report November 1, 2001 - Report: Approved by Office Director - NTSB case key (mKey): 49002 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX00TA163 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/49002/pdf - Page: https://openairdocs.org/ntsb/LAX00TA163 ## Probable cause Company maintenance personnel's failure to secure an attachment nut to a control link. While maneuvering, the parts separated and resulted in the total cyclic control system failure and impact into rough terrain. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, maneuvering - rotorcraft flight control,cyclic control - not safetied (contributing factor) - maintenance,100-hour inspection - improper, company maintenance personnel (cause) - rotorcraft flight control,cyclic control - failure,total (cause) - In flight collision with terrain/water, descent - uncontrolled - terrain condition - rough/uneven - aircraft control - not possible, pilot in command ## Analysis While maneuvering about 20 feet above obstacles looking for the footprints of a group of suspected illegal entrants, the U.S. Border Patrol pilot suddenly experienced an unusual vibration in the cyclic control. After the vibration started, the helicopter almost immediately started turning right and descended. The pilot attempted to stop the turn and descent, but to no avail, and he crashed in the rough terrain. The previous day a 300-hour inspection had been completed by Border Patrol mechanics, and it involved a rebuild of the swashplate assembly. During this maintenance, the cyclic control's longitudinal link (part number 369A7608) was removed and replaced at the stationary swashplate. Upon completion of the maintenance, a cotter pin is required to be installed in the link's attachment nut to secure it. The cotter pin, and the respective nut, were observed missing at the accident site. During the recent maintenance, a mechanic had failed to reinstall the cotter pin into the nut, and it backed off during flight. This maintenance oversight-related failure resulted in the pilot's complete loss of cyclic control. ## Factual narrative HISTORY OF FLIGHT On April 20, 2000, about 0715 hours mountain standard time, a Hughes OH-6A, N61869, operated by the Department of Justice, U.S. Border Patrol Air Operations, experienced an in-flight control system failure while maneuvering southwest of Green Valley, Arizona. The helicopter crashed in rough terrain and was substantially damaged. The commercial pilot received minor injuries. Visual meteorological conditions prevailed during the public-use flight, which was performed under 14 CFR Part 91. A company flight plan was filed for the flight that originated from Tucson, Arizona, at 0600. The pilot, who has over 19,000 hours of flight time, including 3,326 hours in the accident model of helicopter, reported that seconds prior to losing control of the helicopter, he had been flying about 20 feet above obstacles looking for the footprints of a group of suspected illegal entrants. He suddenly experienced an "unusual vibration in the cyclic control." After the vibration started, the helicopter almost immediately started turning slightly right and descending. The pilot stated that he immediately attempted to stop the turn and descent, but to no avail. HELICOPTER MAINTENANCE INFORMATION The operator reported that the accident occurred during the helicopter's first operational flight following completion of a 300-hour inspection, performed by U.S. Border Patrol mechanics. The inspection was completed on April 19, 2000, and, in part, involved maintenance to the main rotor hub (swashplate assembly). The rebuild of the rotor hub included removal and replacement of several bearings, the main rotor blade pitch control links, the main rotor droop stop ring, and several other components. During this maintenance, the longitudinal link (part number 369A7608) was removed and replaced. WRECKAGE AND IMPACT INFORMATION An examination of the wreckage revealed that the longitudinal link that connects the stationary swashplate to the longitudinal pitch mixer bellcrank was observed disconnected at the stationary swashplate. The link's attachment nut and its respective cotter key were not found. In addition, the right-hand link (part number 369A7613) that connects the stationary swashplate to the lateral mixer bellcrank was found fractured. Its respective bolt was missing its required cotter key and the top nut was found backed off and retained on the bolt by approximately three bolt threads. No other evidence of preimpact discrepancies in the flight control system was noted. TESTS AND RESEARCH The operator indicated that an in-flight disconnect of the longitudinal link would result in a complete loss of cyclic control. ## Aircraft - Registration: [N61869](https://openairdocs.org/deregistered/N61869-2005-02-16), registration cancelled 2005-02-16, S/N 69-16002 (OpenAirDocs) - Reported make and model: Hughes OH-6A - Registry model: [Hughes OH-6A](https://openairdocs.org/model/hughes-oh-6a) (registry code 4470905) (OpenAirDocs) - Category: Helicopter - Serial number: 69-16002 - Airframe hours: 7603 - Engines: Allison 250-C20B 300 horsepower turbo shaft - Damage: Substantial damage - Flight: Public aircraft, Part 91 - Registered owner: U.S. Border Patrol Air Ops. - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, April 19, 2000, 2 hours before - Departed: TUS, TUCSON, AZ - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 54; commercial, flight instructor; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane, helicopter; medical: class 2, valid medical--w/ waivers/lim; seat: right; flight hours: 19,560 total, 3,326 in this make and model, 19,201 as pilot in command, 287 in the last 90 days, 93 in the last 30 days, 8 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 130° at 10 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 131 °F, dew point 77 °F - Altimeter: 30.00 inHg - Observed at: TUS, 23 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20000420036799A](https://openairdocs.org/incident/20000420036799A), Apr 20, 2000: Hughes OH6A, Green Valley, AZ, No damage. (-23) On April 20, 2000, at approx. 0730 local time, N61869, HU-369-0H6A, operated by the U.S. Border patrol air operations unit, made a forced landing near… 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.