# NTSB LAX01LA243: Bell 206B, N474SF, San Francisco, CA, July 12, 2001 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 12, 2001, 13:30 local (20:30 UTC) - Place: San Francisco, CA - Coordinates: 37.610397, -122.380706 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=37.6104&lon=-122.3807&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed, report June 25, 2003 - Report: Approved by Office Director - Parties: FEDERAL AVIATION ADMINISTRATION, ROLLS-ROYCE CORPORATION - NTSB case key (mKey): 52694 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX01LA243 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/52694/pdf - Page: https://openairdocs.org/ntsb/LAX01LA243 ## Probable cause The failure of the accessory gearbox 2 1/2 bearing in fatigue resulting in the complete loss of engine power and a subsequent forced landing. The pilot's failure to maintain directional control during the autorotational flare maneuver is also causal. The operator's failure to comply with the recommendations in the engine service manual regarding removal of the engine from service for detailed inspection is a factor. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, cruise - maintenance,service bulletin/letter - not complied with, company/operator management (contributing factor) - accessory drive assy,drive bearing - fatigue (cause) - accessory drive assy - fractured (cause) - Forced landing, emergency descent/landing - autorotation - initiated, pilot in command - Hard landing, landing - flare/touchdown - terrain condition - ground - directional control - not maintained, pilot in command (cause) - flare - inadequate, pilot in command (cause) - rotor system,main rotor - blade strike - misc rotorcraft,main rotor/tail boom contact ## Analysis The helicopter made a hard landing and severed the tail boom after an in-flight engine failure and autorotation. The pilot reported seeing an engine chip light and hearing a whining sound in the engine about 700 feet agl. An engine out light followed by a complete engine failure occurred about 1 minute later. The pilot had been descending to land in an open field by that time. The collective was lowered to enter an autorotation and aft cyclic applied to slow the forward airspeed. As he neared the bottom of the maneuver, he pulled collective pitch to cushion the landing; however, the helicopter abruptly spun 90 degrees to the left. The main rotor blades struck the tail boom and the ground. The tail boom was separated from the helicopter. After an inspection and teardown of the engine, the 2 1/2 bearing was found to have failed in fatigue. Records revealed that a chip light had been reported in the same helicopter on a flight (4) days prior. Before being returned to service, a magnetic plug inspection/cleaning and an engine ground test run were performed. According to the Allision 250 Series Operation and Maintenance Manual, when either a chip light is encountered after a gearbox flush and a second ground test run has been performed or when a total of (4) chip lights have been encountered within 50 hours of engine operation, the engine must be removed from service and sent to the manufacturer's authorized maintenance center. ## Factual narrative On July 12, 2001, at 1330 Pacific daylight time, a Bell 206B, N474SF, lost engine power and made a hard landing from an autorotation in an open field near San Francisco, California. The helicopter sustained substantial damage. The certificated commercial pilot and three passengers were uninjured. San Francisco Helicopter Tours was operating the helicopter as a for-hire sightseeing flight under the provisions of 14 CFR Part 91 when the accident occurred. The local flight originated from San Francisco International Airport at 1317. Day visual meteorological conditions prevailed at the time, and a company VFR flight plan was filed. The pilot reported that he was inbound to the airport when he saw an engine chip light illuminate, and heard a whining sound. He was looking for a suitable landing area when the "engine out" caution light and aural warning activated. An engine failure followed at approximately 400 feet agl (above ground level). The helicopter had been descending to land over a large, flat, open field at the time. The collective was lowered to enter an autorotation and aft cyclic applied to slow the forward airspeed. As he neared the bottom of the maneuver, he pulled collective pitch to cushion the landing; however, the helicopter abruptly spun 90 degrees to the left. The main rotor blades struck the tail boom and the ground. The tail boom was separated from the helicopter. All the occupants were able to exit the helicopter without assistance. A postcrash examination of the engine was conducted with the assistance of Rolls-Royce/Allison. It was disassembled and both the compressor and turbine were reported to have rotated freely. The accessory gearbox was found fractured, however. There was damage to the 2 1/2 bearing, fuel control/generator idler gear, and spur adapter gear shaft. The 2 1/2 bearing had (3) fractured separator rails. Individual bearing rollers displayed uneven wear. Further metallurgical examination revealed an overheated microstructure in the roller path of the 2 1/2 bearing, and that the bearing itself had failed in fatigue. Aircraft logbooks did not reveal any recent maintenance inside the accessory case. The accessory gearbox was last opened for a 2 1/2 bearing replacement in 1990. The manufacturer's guidelines for a teardown inspection of the accessory gearbox and 2 1/2 bearing are on condition only. An engine chip light history existed on the helicopter. The Daily Flight Sheet record indicated another warning had been encountered on a flight 4 days prior. According to San Francisco Helicopters, maintenance personnel followed the published procedure after this occurrence. There was a paste buildup found and mechanics performed a cleaning and inspection of the plugs. Then the engine received a ground test run, at which time no warning lights were observed. The engine and helicopter were returned to service and a corresponding notation was recorded in the helicopter's logbook. The published maintenance manual procedure calls for a nondestructive inspection/cleaning of the magnetic chip detectors and then an engine ground test run for 30 minutes. The chip light would illuminate if metal particles collected on the magnetic plugs in the accessory gear drive housing. According to the Allision 250 Series Operation and Maintenance Manual, when either a chip light is encountered after a gearbox flush and a second ground test run has been performed or when a total of (4) chip lights have been encountered within 50 hours of engine operation, the engine must be removed from service and sent to the manufacturer's authorized maintenance center. ## Aircraft - Registration: [N474SF](https://openairdocs.org/deregistered/N474SF-2004-04-28), registration cancelled 2004-04-28, S/N 1526, built 1975 (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 400HP](https://openairdocs.org/engine/allison-250-ser-400hp) (registry code 03013, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 1526 - Airframe hours: 5876 - Engines: Allison 250-C20 400 horsepower turbo shaft - Damage: Substantial damage - Flight: Business, Part 91 - Operator: Mcclelland, John And Teri, doing business as San Francisco Air Tours - Registered owner: McClelland, John and Teri - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, April 25, 2001, 99.5 hours before - Departed: SFO, San Francisco, CA - Destination: SFO, San Francisco, CA - Flight plan: Company VFR - Airport: SFO, San Francisco International ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 30; injuries: none; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane, helicopter; medical: class 1, valid medical--no waivers/lim.; last flight review July 27, 2000; seat: right; flight hours: 1,305 total, 860 in this make and model, 1,000 as pilot in command, 134 in the last 90 days, 44 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 250° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: 1,800 ft overcast - Temperature: 64 °F, dew point 54 °F - Altimeter: 30.09 inHg - Observed at: KSFO ## 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 20010712018899A](https://openairdocs.org/incident/20010712018899A), Jul 12, 2001: Bell 206B, Sanfrancisco, CA, No damage. (.19) On July 12, 2001, at 1330 hours pacific daylight time, a Bell 206B, N474SF, lost engine power and made a hard landing from an autorotation in san… 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.