# NTSB CHI06GA174: Bell UH-1H, N681FD, Chicago, IL, June 30, 2006 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Final report - Date: June 30, 2006, 12:00 local (17:00 UTC) - Place: Chicago, IL - Coordinates: 41.838054, -87.603332 - Nearby events: https://openairdocs.org/map.md?lat=41.8381&lon=-87.6033&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 3 minor, 1 uninjured - Status: Completed, report March 31, 2008 - Report: Approved by Office Director - Parties: Bell Helicopter, City of Chicago Fire Department - Air Sea Rescue, Federal Aviation Administration - DuPage FSDO - NTSB case key (mKey): 64038 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI06GA174 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/64038/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=64038 - Page: https://openairdocs.org/ntsb/CHI06GA174 ## Probable cause The in-flight separation of a tail rotor driveshaft hanger bearing due to inadequate maintenance performed by maintenance personnel. Contributing to the accident was the inability to maintain directional control due to the lack of tail rotor thrust. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - normal - maintenance,inspection - inadequate, company maintenance personnel (cause) - misc rotorcraft - separation (cause) - Forced landing, emergency descent/landing - autorotation - performed, pilot in command - Roll over, emergency descent/landing - directional control - not possible (contributing factor) ## Analysis The public-use helicopter was responding to an emergency when it had a vibration and yawed to the right during cruise flight. It subsequently had a loss of tail rotor thrust. The pilot reduced engine power and made an autorotation to a park along the lakeshore. During landing flare, the helicopter yawed left as the pilot increased collective prior to touchdown. He stated that the touchdown "seemed smooth" and was made on the aft-portion of the skids, but as the helicopter slowed the left yaw tendency increased. The helicopter rolled over and came to rest inverted at the completion of the run-on landing. Examination of the helicopter revealed that the number-one tail rotor driveshaft hanger assembly had separated, resulting in a discontinuity of the tail rotor driveshaft. The machine bolt that held the assembly together was not installed with the required cotter pin. Further examination of the hanger assembly revealed that the splined areas did not contain grease. The remaining tail rotor driveshaft hanger bearings were properly greased and assembled. The mechanic who worked on the helicopter reported that due to other workload items, the previous tail rotor driveshaft inspection was interrupted several times before he was able to complete all of the required tasks. To avoid inter-mixing the driveshaft components, he temporarily reassembled the hanger assemblies before working on other projects. His intention was to disassemble each hanger bearing when he had the opportunity to complete the inspection. The mechanic stated that he must have forgotten to disassemble, inspect, and grease the number one hanger assembly. At the time of the accident, the number one hanger assembly had accumulated about 33 hours since the inspection. ## Factual narrative HISTORY OF FLIGHT On June 30, 2006, at 1200 central daylight time, a Bell UH-1H helicopter, N681FD, operated by the City of Chicago Fire Department, was substantially damaged during a forced landing after experiencing a loss of tail rotor thrust while in cruise flight over Chicago, Illinois. Visual meteorological conditions prevailed at the time of the accident. The public-use flight was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The pilot-in-command (PIC) and two passengers (rescue divers) sustained minor injuries. The second-in-command (SIC), the remaining occupant, was not injured. The local area flight departed from the Chicago Fire Department Air Sea Rescue Heliport (LL35), Chicago, Illinois. At 1143, the flight crew was dispatched to the scene of a drowning victim in Lake Michigan. At 1150, the pilot performed an uneventful departure and proceeded northbound over Lake Michigan toward the location of the drowning. While in cruise flight at 1,200 feet mean sea level (msl), the helicopter "experienced a vibration and a slight yaw of the nose to the right." The pilot did not notice any anomalies after scanning the instrument panel. The helicopter then experienced another set of vibrations and experienced additional yawing to the right. The pilot reported that his "suspicions of tail rotor failure were being confirmed" and he elected to head for an open area along the lakeshore as a precaution. A few moments later, the helicopter again experienced more vibrations and yawed about 45-degrees to the right. The pilot reduced engine power, which "seemed to reduce the yaw angle somewhat" and then performed an autorotation to the open area ahead of the helicopter. During landing flare the helicopter yawed left as the pilot increased collective prior to touchdown. He stated that the touchdown "seemed smooth" and was made on the aft-portion of the skids, but as the helicopter slowed the left yaw tendency increased. When the helicopter had almost stopped, the pilot "sensed that the [helicopter] was tipping over slowly on its right side" and it subsequently rolled inverted. PERSONNEL INFORMATION Pilot-in-Command (PIC) According to Federal Aviation Administration (FAA) records, the PIC of N681FD, age 52, held a commercial certificate with rotorcraft-helicopter, airplane single-engine land, airplane multiengine land, and instrument airplane ratings. The PIC was also a certified flight instructor for single-engine and multi-engine land airplanes. The PIC's last aviation medical examination was completed on May 27, 2006, when he was issued a second-class medical certificate with the limitation "shall possess glasses that correct for near vision." According to fire department information, the PIC had accumulated 1,814 hours total flight time. He had flown 781 hours in rotorcraft, 783 hours in single-engine airplanes and 250 hours in multiengine airplanes. He had accumulated 740 hours as PIC in rotorcraft. The PIC had flown 200 hours in a Bell UH-1H helicopter. His last flight review was completed on January 26, 2006, in a Bell 412EP Level D Simulator at Flight Safety International. Second-in-Command (SIC) According to FAA records, the SIC of N681FD, age 50, held a commercial certificate with rotorcraft-helicopter and airplane single-engine land ratings. The airplane single-engine land rating was limited to private pilot privileges. The SIC's last aviation medical examination was completed on June 19, 2006, when he was issued a second-class medical certificate with no restrictions or waivers. According to fire department information, the SIC had accumulated 329 hours total flight time. He had flown 196 hours in rotorcraft and 133 hours in single-engine airplanes. He had accumulated 30 hours as PIC in rotorcraft. The SIC had flown 3 hours in a Bell UH-1H helicopter. His last flight review was completed on April 13, 2006, in a Bell 206B-3 helicopter. AIRCRAFT INFORMATION The 1965 Bell UH-1H helicopter, serial number 65-10101, manufacturer ship number 5145, was a military surplus aircraft. In 1995, the Chicago Fire Department acquired the helicopter from the Illinois National Guard after it was retired from military service. The helicopter had a two-bladed main rotor system and was powered by a single 1,250 horsepower Honeywell T53-L-13BA turbo shaft engine. The accident helicopter was configured to accommodate a pilot and seven passengers. The helicopter's maximum gross weight was 9,500 lbs. The helicopter was approved for single-pilot operations. At the time of the accident, the airframe had accumulated about 5,278 hours and the engine had accumulated about 2,511 hours. The helicopter had accumulated about six hours since the last maintenance inspection, which was completed on June 27, 2006. METEOROLOGICAL INFORMATION The closest weather reporting facility was at the Chicago Midway International Airport (MDW), about 7.2 nautical miles west-southwest of the main wreckage. The airport was equipped with an automated surface observing system (ASOS). At 1153 central daylight time, the MDW ASOS reported the following weather conditions: Wind 220 degrees true at 8 knots; visibility 10 statute miles; few clouds at 12,000 feet above ground level (agl) and scattered clouds at 20,000 feet agl; temperature 27 degrees Celsius; dew point 13 degrees Celsius; altimeter setting 30.07 inches of mercury. FLIGHT RECORDERS The accident helicopter was not equipped, nor was it required to be equipped, with a cockpit voice recorder or flight data recorder. WRECKAGE AND IMPACT INFORMATION The helicopter landed in a park area along the Lake Michigan shoreline. There were four ground scars in the turf preceding the main wreckage. These ground scars were consistent with the helicopter's ground track during landing. The ground scars curved from a northerly to northwesterly heading and collectively measured about 65 feet long. The helicopter was inverted, laying on its roof structure. Both the main transmission and its rotor system separated from the fuselage and were lying next to the cabin. A main rotor blade tip was found about 460 feet southwest of the main wreckage. The tailboom assembly remained attached to the cabin structure and the tail rotor remained attached to its gear box. The tail rotor system did not have any noticeable blade damage. Examination of the helicopter revealed that the number-one tail rotor driveshaft hanger assembly (p/n 204-040-600-11) had separated, resulting in a discontinuity of the tail rotor driveshaft. The machine bolt (p/n AN4-30) that held the assembly together was not installed with the required cotter pin (p/n MS24665-155). Further examination of the hanger assembly revealed that the splined areas did not contain grease. The remaining tail rotor driveshaft hanger bearings were properly greased and assembled. SURVIVAL ASPECTS The accident helicopter was commonly used to patrol Chicago's Lake Michigan shoreline during search and rescue operations. During these operations, two rescue divers would accompany the flightcrew during flight. The cabin seating provided for the divers did not accommodate their self-contained underwater breathing apparatus (SCUBA) air tanks. In order to facilitate getting the rescue divers on-scene as soon as possible, the divers wore their SCUBA air tanks while in flight. While the helicopter was patrolling the lakeshore or enroute to an emergency, the rescue divers would sit on the forward edge of their respective seats due to the interference of their air tanks. As a result, the rescue divers would not be fully seated in their seats and could not use their supplied lap belts. Both rescue divers reported minor injuries from being unrestrained in the cabin during the accident landing. A majority of the accident aircraft's missions were performed over Lake Michigan. The helicopte ## Aircraft - Registration: N681FD (not matched to a registry record) - Reported make and model: Bell UH-1H - Category: Helicopter - Serial number: 65-10101 - Airframe hours: 5278 - Engines: Honeywell International Inc. T53-L-13BA 1250 horsepower turbo shaft - Damage: Substantial damage - Flight: Public aircraft - local, Public use - Registered owner: City of Chicago Fire Department - Last inspection: AAIP, June 1, 2006, 6 hours before - Departed: LL35, Chicago, IL - Destination: LL35, Chicago, IL - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; injuries: minor; commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review January 1, 2006; seat: right; flight hours: 1,814 total, 200 in this make and model, 1,753 as pilot in command, 20 in the last 90 days, 5 in the last 30 days, 0 in the last 24 hours - Co-pilot; age 50; injuries: none; private, commercial; airplane ratings: single-engine land; medical: class 2, without waivers/limitations; last flight review April 1, 2006; seat: left; flight hours: 329 total, 3 in this make and model, 32 in the last 90 days, 2 in the last 30 days, 0 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 220° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 81 °F, dew point 55 °F - Altimeter: 30.06 inHg - Observed at: MDW, 7 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 20060630026979A](https://openairdocs.org/incident/20060630026979A), Jun 30, 2006: Bell UH1H, Chicago, IL, Destroyed. (-23) Aircraft departed 95th st heliport in response to a reported incident in the proximity of north ave beach @ approximately 41st and the lake. An… ## Docket (15 files) The files NTSB released with the investigation on February 22, 2008, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=64038. 5.3 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289230&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Flight Crew Statements (item 2, .PDF, 585 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289231&FileExtension=.PDF&FileName=Flight%20Crew%20Statements-Master.PDF - Mechanic Statement (item 3, .PDF, 86 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289232&FileExtension=.PDF&FileName=Mechanic%20Statement-Master.PDF - Illustrated Parts Catalog - Tail Rotor Driveshaft Hanger Assembly (item 4, .PDF, 469 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289233&FileExtension=.PDF&FileName=Illustrated%20Parts%20Catalog%20-%20Tail%20Rotor%20Driveshaft%20Hanger%20Assembly-Master.PDF - City of Chicago Fire Department Safety Changes (item 5, .PDF, 234 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289234&FileExtension=.PDF&FileName=City%20of%20Chicago%20Fire%20Department%20Safety%20Changes-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 6, .PDF, 124 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289235&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 7, .PDF, 180 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289236&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - Photo 01. Accident Site Overview (item 8, .PDF, 276 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289237&FileExtension=.PDF&FileName=Photo%2001.%20%20Accident%20Site%20Overview-Master.PDF - Photo 02. Accident Site Overview (item 9, .PDF, 277 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289238&FileExtension=.PDF&FileName=Photo%2002.%20%20Accident%20Site%20Overview-Master.PDF - Photo 03. Accident Site Overview (item 10, .PDF, 270 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289239&FileExtension=.PDF&FileName=Photo%2003.%20%20Accident%20Site%20Overview-Master.PDF - Photo 04. Tail Rotor Driveshaft Hanger Assembly Separation (item 11, .PDF, 278 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289240&FileExtension=.PDF&FileName=Photo%2004.%20%20Tail%20Rotor%20Driveshaft%20Hanger%20Assembly%20Separation-Master.PDF - Photo 05. Tail Rotor Driveshaft Hanger Assembly Separation (item 12, .PDF, 250 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289241&FileExtension=.PDF&FileName=Photo%2005.%20%20Tail%20Rotor%20Driveshaft%20Hanger%20Assembly%20Separation-Master.PDF - Photo 06. Tail Rotor Driveshaft Hanger Assembly Layout (item 13, .PDF, 287 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289242&FileExtension=.PDF&FileName=Photo%2006.%20%20Tail%20Rotor%20Driveshaft%20Hanger%20Assembly%20Layout-Master.PDF - Photo 07. Tail Rotor Driveshaft Hanger Assembly Layout (item 14, .PDF, 264 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289243&FileExtension=.PDF&FileName=Photo%2007.%20%20Tail%20Rotor%20Driveshaft%20Hanger%20Assembly%20Layout-Master.PDF - Photo 08. Tail Rotor Driveshaft Hanger Assembly Layout (item 15, .PDF, 294 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40289258&FileExtension=.PDF&FileName=Photo%2008.%20%20Tail%20Rotor%20Driveshaft%20Hanger%20Assembly%20Layout-Master.PDF 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.