# NTSB FTW98LA260: Bell 206B, N16814, Corpus Christi, TX, June 7, 1998 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 7, 1998, 17:44 local (22:44 UTC) - Place: Corpus Christi, TX - Coordinates: 27.799324, -97.389335 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=27.7993&lon=-97.3893&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed, report May 11, 1999 - Report: Approved by Office Director - NTSB case key (mKey): 20642 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW98LA260 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/20642/pdf - Page: https://openairdocs.org/ntsb/FTW98LA260 ## Probable cause The failure of the tail rotor drive shaft due to the separation of a bolt at one of the drive shaft disc couplings for an undetermined reason, which resulted in the pilot's inability to maintain directional control during landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, approach - vfr pattern - final approach - miscellaneous,bolt/nut/fastener/clamp/spring - separation (cause) - reason for occurrence undetermined (cause) - rotor drive system,tail rotor drive shaft - failure (cause) - Forced landing, approach - autorotation - performed, pilot in command - Hard landing, landing - flare/touchdown - directional control - not possible, pilot in command (cause) ## Analysis The helicopter experienced a tail rotor drive shaft failure while on final approach to landing. Approximately 45 to 50 feet AGL, the pilot heard a 'loud snapping sound,' which was followed by a 'loss of tail rotor control.' An autorotation was initiated, and subsequently, the helicopter landed 'hard' on the grassy staging field and came to a stop upright. Examination of the helicopter revealed that two of the tail rotor drive shaft segments were fractured. Additionally, one of the two bolts connecting the aft end of one of the fractured segments to a disc coupling (Thomas Coupling) was missing. The missing bolt was not recovered, although a nut and two beveled washers were found on top of the tail boom beneath the driveshaft. An examination of the remaining bolt revealed that it exhibited fretting, wear and deformation to only the last two and one-half threads. Review of the maintenance records revealed no entries indicating that any of the tail rotor drive shaft segments were removed in the two years preceding the accident. ## Factual narrative On June 7, 1998, at 1744 central daylight time, a Bell 206B helicopter, N16814, registered to and operated by Houston Helicopters, Inc., was substantially damaged during a hard landing following the failure of the tail rotor drive shaft in Corpus Christi, Texas. The commercial pilot and the three passengers were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the Title 14 CFR Part 135 sightseeing flight. The local flight originated from a hotel parking lot in Corpus Christi at 1646. According to the pilot, the flight was returning to the hotel after observing a boat race. While on final approach to the staging area, approximately 45 to 50 feet AGL, the pilot heard a "loud snapping sound." He stated that the helicopter experienced a "loss of tail rotor control," and he initiated an autorotation. Subsequently, the helicopter landed "hard" on the grassy staging field and came to a stop upright. An FAA inspector examined the helicopter at the site. He reported that the tail boom was bent, and the skids were spread. The number two and number three tail rotor drive shaft segments (first and second segments aft of the oil cooler) were fractured. One of the two bolts attaching the aft end of the number three tail rotor drive shaft segment to the disc coupling (Thomas coupling) was missing, and the other bolt was loose. A nut and two beveled washers were found resting on the tail boom beneath the driveshaft; the missing bolt was not found. Review of the helicopter's maintenance records revealed no entries indicating that any of the tail rotor drive shaft segments were removed in the two years preceding the accident. According to the maintenance records, the helicopter's most recent annual inspection was completed on April 21, 1998, at 10,054.1 hours. Review of the checklist for the April 21st inspection indicated that the drive shaft (disc) couplings were inspected for condition and security. At the time of the accident, the helicopter had accumulated a total of 52.5 hours since this inspection. The number two, number three, and number four tail rotor drive shaft segments, the hardware between the number three segment and the number four segment (including the disc coupling), and the nut and two beveled washers were examined under the supervision of the NTSB investigator-in-charge at the Bell Helicopter Engineering Laboratories, Hurst, Texas. The examination revealed that the number two segment (first drive shaft segment aft of the oil cooler) was fractured 6 inches from the forward end. The number three segment (second segment aft of the oil cooler) was fractured 14.5 inches from the forward end. According to the Bell metallurgist, both fractures exhibited signatures typical of bending and torsional overload. The remaining bolt joining the aft section of the number three drive shaft segment to the disc coupling was removed and examined. The bolt threads exhibited fretting, wear, and deformation to only the last two and one-half threads, and the bolt was bent along the shank. The discs of the coupling assembly in the area where the bolt was attached were deformed and spread open. The inside diameter of the bolt hole in the discs was worn, fretted and deformed. No torque paint was found on the bolt, washers, or nut. The opposite hole in the discs, from which the bolt was missing, was not "extensively" damaged. The discs surrounding this hole were "relatively flat," with no evidence of permanent deformation or spread. The nut and two beveled washers found resting on the tailboom were examined. The internal threads on the nut and the washer mating surfaces were "relatively undamaged." No torque paint was found on the washers or nut. Thread and head imprints from a bolt were found on the third drive shaft segment approximately one inch aft of the fracture surface. The imprints were adjacent to the disc coupling from which the bolt was missing and corresponded to the size of a AN174-7A bolt, which was the size of the missing bolt. ## Aircraft - Registration: [N16814](https://openairdocs.org/deregistered/N16814-2010-06-14), registration cancelled 2010-06-14, S/N 2229, built 1977 (OpenAirDocs) - Reported make and model: Bell 206B - Registry model: [Bell 206B](https://openairdocs.org/model/bell-206b) (registry code 1181511) (OpenAirDocs) - Registry engine: [Allison 250 SER 250HP](https://openairdocs.org/engine/allison-250-ser-250hp) (registry code 03002, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 2229 - Airframe hours: 10107 - Engines: Allison 250-C20B 420 horsepower turbo shaft - Damage: Substantial damage - Flight: Part 135 - Registered owner: Houston Helicopters, Inc. - Airworthiness certificate: Standard, Normal - Last inspection: Annual, April 21, 1998, 53 hours before ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 45; commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; seat: right; flight hours: 9,583 total, 3,072 in this make and model, 9,434 as pilot in command, 105 in the last 90 days, 21 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 90° at 18 knots, gusting 25 - Visibility: 7 statute miles - Lowest ceiling: 1,500 ft broken - Temperature: 90 °F - Altimeter: 30.00 inHg ## 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 19980607012449A](https://openairdocs.org/incident/19980607012449A), Jun 7, 1998: Bell 206B, Corpus Christi, TX, Substantial damage. Snapping sound on approach. Lost tailrotor control. Auto rotated hard ldg. Sread skids. Chopped tail broke shaft. (.4) the helicopter experienced a tail rotor… ## Other investigations on N16814 (1) 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. - [NTSB FTW93LA228](https://openairdocs.org/ntsb/FTW93LA228), Aug 4, 1993: Bell 206B (N16814), Pearland, TX, substantial damage. Probable cause: PILOT'S FAILURE TO MAINTAIN PROPER ROTOR RPM, THE DELAYED FLARE, AND IMPROPER TOUCHDOWN. FACTORS WERE TOTAL FAILURE OF THE POWER TURBINE DUE TO OIL STARVATION TO THE #8 BEARING ASSEMBLY. 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.