# NTSB LAX98LA108: Bell UH-1B, N204DR, Hollister, CA, March 7, 1998 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: March 7, 1998, 09:56 local (17:56 UTC) - Place: Hollister, CA - Coordinates: 36.889377, -121.240936 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.8894&lon=-121.2409&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious - Status: Completed, report August 3, 1999 - Report: Approved by Office Director - NTSB case key (mKey): 30047 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX98LA108 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/30047/pdf - Page: https://openairdocs.org/ntsb/LAX98LA108 ## Probable cause The failure of the maintenance personnel to recognize and repair the chafed area of the tail rotor driveshaft, which resulted in an in-flight separation of the tail fin and hub assembly. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, maneuvering - aerial application - vertical stabilizer - fatigue - maintenance,inspection - inadequate, company maintenance personnel (cause) - vertical stabilizer - separation - rotor drive system,tail rotor gearbox(90 deg) - separation - Loss of control - in flight, maneuvering - aerial application - rotor drive system,tail rotor gearbox(90 deg) - separation - aircraft control - not possible, pilot in command - In flight collision with terrain/water, descent - uncontrolled ## Analysis The pilot initiated a right turn, then he felt and heard a thump. He lowered the collective and attempted to straighten from the turn. He felt a strong vibration and the nose of the aircraft pitched down. A ground crewman who witnessed the accident reported that while the helicopter was about 35 feet agl, he saw a large piece of the tail and a rotor blade fly off the ship, followed by the tail rotor hub assembly, the remaining blade, and the 90-degree gearbox. The helicopter began a 360-degree right spiral, made 2 1/2 rotations, and then impacted the ground in a 30-degree nose-down attitude. He further noted that the engine still seemed to be producing about 60 percent power. The tail and tail rotor gearbox was found about 125 feet from the fuselage. Metallurgical examination of the vertical tail fin, tail rotor gearbox, and tail rotor blades disclosed an area of chafing which wore through the vertical fin's spar and initiated a fatigue crack. The fatigue crack initiated in an area where the vertical fin driveshaft cover fastened on the left side of the aircraft near the upper end. Chafing had occurred between the cover and the spar, wearing away the spar. According to Bell, the UH-1B requires a daily inspection to visually check the area of the upper vertical fin, per the Aviation Unit Technical Manual, where the fatigue cracking occurred. ## Factual narrative On March 7, 1998, at 0956 hours Pacific standard time, a Bell UH-1B, N204DR, crashed near Hollister, California, following a separation of the tail rotor gear box. The aircraft was destroyed and the commercial pilot, the sole occupant, suffered serious injuries. Visual meteorological conditions prevailed and no flight plan was filed. The flight was operated by Cantrell Helicopters under 14 CFR Part 137. The pilot reported that he was spraying a field approximately 1-mile northeast of Hollister. At the end of his third pass over the field, he pulled up to go over power lines and was starting a right turn when he felt and heard a thump. He lowered the collective and attempted to straighten out from the right turn. The pilot stated that a strong vibration started and the nose of the aircraft pitched down. The helicopter started a right turn, which began increasing in momentum. The pilot's memory of the event ceases at this point. There was a ground crewman in the field who witnessed the accident. The witness stated that while the pilot was making a pass down the field about 35 feet agl, he saw a large piece of the tail rotor blade fly off the ship, followed by the tail rotor hub assembly, the remaining blade, and the 90-degree gearbox. The helicopter started into a 360-degree spiral to the right, made 2 1/2 rotations, then impacted the ground in a 30-degree nose-down attitude. The witness helped the pilot exit the helicopter and noted that the engine was still producing about 60 percent power. A Federal Aviation Administration inspector from the San Jose Flight Standards District Office responded to the accident site and examined the wreckage. The tail fin and tail rotor gearbox was found approximately 125 feet from the fuselage. The tail rotor gearbox and tail rotor blades were examined at the Bell Helicopter Textron Materials Laboratory in Fort Worth, Texas, under the supervision of the Safety Board. A copy of their report is appended to this file. Their report was forwarded to the Safety Board's Materials Laboratory for review. The Bell metallurgist reported that examination of the tail vertical fin disclosed an area of chafing which wore through the spar and initiated a fatigue crack. The fatigue crack initiated in an area where the vertical fin driveshaft cover fastened on the left side of the aircraft near the upper end. Chafing had occurred between the cover and the spar, wearing away the spar. The primary fatigue crack initiated in the worn area, but the origin of the crack had been destroyed. The fatigue crack propagated from the spar downward through eight rivet holes in the skin a distance of 7 inches, then turned aft a distance of 3.8 inches. The fatigue crack propagated through the entire width of channel a distance of 6.5 inches and through the five areas of the stiffener. The fatigue cracking in the vertical fin covered 65 to 75 percent of the structure's cross section. According to Bell, the UH-1B helicopter requires a daily inspection to visually check the area of the upper vertical fin, per the Aviation Unit Technical Manual (55-1520-219-PMS), where the fatigue cracking occurred. The operator reported that he did not have the aircraft logbooks in his possession, therefore the Safety Board conducted no review. ## Aircraft - Registration: [N204DR](https://openairdocs.org/deregistered/N204DR-2013-08-21), registration cancelled 2013-08-21, S/N 62-1881 (OpenAirDocs) - Reported make and model: Bell UH-1B - Registry model: [Bell UH-1B](https://openairdocs.org/model/bell-uh-1b) (registry code 1181410) (OpenAirDocs) - Category: Helicopter - Serial number: 62-1881 - Engines: Lycoming T53L-11 1100 horsepower turbo shaft - Damage: Destroyed - Flight: Aerial application, Part 137 - Operator: Cantrell Helicopters - Registered owner: Del Rio Aviation - Airworthiness certificate: Special, Restricted (Special) - Departed: 307, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 38; commercial, flight instructor, private; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: right; flight hours: 1,144 total, 40 in this make and model, 1,062 as pilot in command, 102 in the last 90 days, 30 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 20 statute miles - Lowest ceiling: 6,000 ft broken - Temperature: 48 °F, dew point 37 °F - Altimeter: 30.00 inHg - Observed at: RHV, 27 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 19980307002829A](https://openairdocs.org/incident/19980307002829A), Mar 7, 1998: Bell UH1B, Hollister, CA, Destroyed. Tail rotor gear box seperated during spray run. Spiralled to ground. (.4)the pilot initiated a right turn, then he felt and heard a thump. He lowered the… 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.