# NTSB FTW98TA104: Hughes 269C, N1093N, Brackettville, TX, January 22, 1998 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Final report - Date: January 22, 1998, 10:15 local (16:15 UTC) - Place: Brackettville, TX - Coordinates: 29.309896, -100.409317 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=29.3099&lon=-100.4093&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor, 1 uninjured - Status: Completed, report October 30, 1998 - Report: Approved by Office Director - NTSB case key (mKey): 20685 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW98TA104 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/20685/pdf - Page: https://openairdocs.org/ntsb/FTW98TA104 ## Probable cause failure of splines on the drive shaft coupling after separation of the forward bubber boot and loss of lubrication (grease), which resulted in a disconnect of the rotor drive system and an autorotation/forced landing. Lack of suitable terrain in the forced landing area was a related factor. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - lubricant,grease - loss,total (cause) - rotor drive system - failure (cause) - rotor drive system,engine to transmission drive - disconnected (cause) - Forced landing, emergency descent/landing - autorotation - performed, pilot in command - On ground/water encounter with terrain/water, emergency landing - terrain condition - none suitable (contributing factor) - terrain condition - rough/uneven (contributing factor) ## Analysis The pilot and a crewmember/gunner of the public use helicopter reported hearing a loud squealing noise, emanating from the rear of the helicopter, while in flight at 75 feet AGL. Rotor RPM began decaying from 3,100 to approximately 2,000 RPM, and the pilot initiated an autorotation. During the landing, the main rotor blades contacted the ground, and helicopter came to rest in a rocky dry creek bed on its right side. The tension nut for the short shaft was found upstream from the point of impact. An examination revealed that splines for the drive shaft coupling were damaged, and the plating on the adapter was discolored as result of excessive heat. Further examination revealed that the damage sustained by the shaft and adapter were consistent with loss of grease and subsequent overheating and destruction of the drive splines. The forward rubber boot, used to retain the lubricant, had separated, resulting in the loss of lubrication. ## Factual narrative On January 22, 1998, at 1015 central standard time, a Hughes 269C helicopter, N1093N, was substantially damaged following a loss of power while in cruise flight near Brackettville, Texas. The helicopter was owned by Go Helicopters of Houston, Texas, and was being operated by the United states Department of Agriculture, under Title 14 CFR Part 91. The airline transport rated pilot was not injured and the crewmember/gunner sustained minor injuries. Visual meteorological conditions prevailed throughout the area for the local coyote eradication flight for which a flight plan was not filed. The public use flight originated from the Bacon Ranch, located approximately 6 miles from the accident site, at approximately 0914. According to the pilot, after one hour of normal operations , with over 30 minutes of fuel remaining, while in cruise flight at 75 feet above the terrain, at an airspeed of 50 knots, a loud squealing noise emanating from the rear of the helicopter was heard by both the pilot and the gunner. The pilot reported that he checked all engine instruments and reported that all systems were normal, and the engine was operating normally. Subsequently, the main rotor RPM began decaying from 3,100 to approximately 2,000 RPM, accompanied by the illumination of the low rotor RPM light. The pilot stated that as turned the helicopter towards the best landing area available, he reduced collective pitch in an attempt to maintain rotor RPM and establish an autorotational glide. Just prior to ground impact, at approximately 10 feet above the ground, the pilot flared the helicopter to arrest his rate of descent and reduce forward airspeed. The pilot further stated that he then leveled the helicopter and applied all remaining collective pitch to cushion the landing. According to the pilot, as the helicopter made contact with the ground, the rear portion of the skids landed on the edge of a creek bed, while the forward portion of the skids rocked forward into the creek bed resulting a rolling motion in the pitch axis which allowed the main rotor blades to contact the ground. The helicopter came to rest in a dry creek bed leaning on its right side. The gunner/observer in the helicopter, who was employed by the State of Texas, as a "Animal Damage Control Specialist," submitted an account of the accident sequence. The gunner added that the helicopter was on a northerly heading, and they were not in pursuit of any animals at the time that the emergency developed. He further stated that he was able to make a distress call on his radio while the pilot was entering autorotation. The gunner stated that he ended up partially pinned in the wreckage, and the pilot was able to raise the helicopter enough for him to egress. Examination of the wreckage by the FAA inspector revealed that the tailboom separated from the airframe and the fuselage sustained structural damage. The inspector reported that the tension nut for the short shaft was found upstream from the point of impact. A conditional released was issued to the insurance adjuster for recovery of the wreckage to a secured location. On February 5, 1998, the wreckage of the helicopter was examined under the supervision of the FAA inspector at Laredo Helicopters in Laredo, Texas. The examination was focused on the helicopter's drive system. The examination revealed that splines for the drive shaft coupling, P/N 269A5559-3, serial number 3922, were damaged and the plating on the adapter was discolored as result of excessive heat. The lower pulley coupling shaft (269A5559), the engine drive adapter (269A5411), the aft pulley nut (269A5415), and plug (269A5419) were shipped to the manufacturer for further examination. The examination revealed that the damage sustained by the shaft and adapter were consistent with loss of grease and subsequent overheating and destruction of the drive splines. The forward rubber boot used to retain the lubricant was missing, and appeared to have separated resulting in the loss of lubricant. See enclosed report for details of the examination. A detailed review of the airframe and powerplant maintenance records for the helicopter was conducted by the FAA inspector. The total time on the helicopter was established at 2,829 hours. The engine (S/N L-22290), which was installed in the helicopter on December 30, 1997, just 18 hours prior to the accident, had accumulated a total of 776 hours since its last overhaul. Copies of pertinent maintenance records are enclosed in this report. The helicopter was not equipped with an emergency locator transmitter (ELT). ## Aircraft - Registration: [N1093N](https://openairdocs.org/deregistered/N1093N-2016-09-01), registration cancelled 2016-09-01, S/N 100882, built 1980 (OpenAirDocs) - Reported make and model: Hughes 269C - Registry model: [Hughes 269C](https://openairdocs.org/model/hughes-269c) (registry code 4470504) (OpenAirDocs) - Registry engine: [Lycoming HIO-360 series](https://openairdocs.org/engine/lycoming-hio-360-series) (registry code 41524, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 100882 - Airframe hours: 2829 - Engines: Lycoming HIO-360-D1A 190 horsepower reciprocating - Damage: Substantial damage - Flight: Public aircraft, Part 91 - Operator: Gary L. Nunley, doing business as U.S. Dpt. Of Agriculture - Registered owner: Gregory M. Obert - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, December 30, 1997, 18 hours before - Departed: BACON RANCH, TX ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 35; flight instructor, airline transport; airplane ratings: single-engine land; instrument ratings: airplane, helicopter; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 12,000 total, 1,500 in this make and model, 10,000 as pilot in command, 200 in the last 90 days, 80 in the last 30 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 360° at 20 knots - Visibility: 10 statute miles - Lowest ceiling: 8,000 ft overcast - Temperature: 45 °F ## 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 19980122003819A](https://openairdocs.org/incident/19980122003819A), Jan 22, 1998: Hughes 269C, Brackettville, TX, Substantial damage. Nsda flight. Loud squeal. Rotor decay. Autorotated dry creek bed. Chopped tail drive adapter lost boot and grease. (-23) the accident occurred approximately 20… 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.