# NTSB LAX04LA176: Bell 47G-4A, N7NB, Bakersfield, CA, April 3, 2004 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: April 3, 2004, 07:45 local (15:45 UTC) - Place: Bakersfield, CA - Coordinates: 35.349998, -119 - Nearby events: https://openairdocs.org/map.md?lat=35.3500&lon=-119.0000&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious - Status: Completed, report December 28, 2004 - Report: Approved by Office Director - Parties: Federal Aviation Administration - NTSB case key (mKey): 59003 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX04LA176 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/59003/pdf - Page: https://openairdocs.org/ntsb/LAX04LA176 ## Probable cause a loss of tail rotor drive due to a disconnection of the drive shaft's splined coupling at the tail rotor gear box. The splined coupling to tail rotor gear box disconnection occurred as a result of tail boom flexing due to the combined effects of an uninstalled structural support tube and a crack in left side frame tubes. Inadequate maintenance inspection was a factor. ## 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 - misc rotorcraft - not installed (cause) - misc rotorcraft,tail boom - cracked (cause) - maintenance,inspection - inadequate, company maintenance personnel (contributing factor) - rotor drive system,tail rotor drive shaft coupling - disconnected (cause) - Loss of control - in flight, maneuvering - aerial application - tail rotor/anti-torque control - not available, pilot in command - In flight collision with terrain/water, descent - uncontrolled - terrain condition - crop ## Analysis The helicopter experienced a loss of tail rotor control and collided with terrain. During an aerial application flight, the pilot heard a rattling noise from the aft end of the helicopter. He then lost tail rotor authority and entered a flat spin. The pilot attempted to make a run-on landing, but the helicopter continued to spin until it impacted terrain. A Federal Aviation Administration inspector examined the helicopter after the accident. He noted that the cross-over support tube near the aft end of the tail boom was missing. A crack was found on the tail boom left side frame tubes. Deposits of rust in the area suggests that the crack was a pre-existing crack. The inspector thought that this would have added excessive stress to the structure during turning maneuvers and caused the last spline coupling shaft to disconnect from the tail rotor gear box as the tail boom flexed. A 50-hour maintenance inspection was completed the day before the accident. ## Factual narrative On April 3, 2004, about 0745 Pacific standard time, a Bell 47G-4A, N7NB, collided with terrain following a loss of tail rotor control near Bakersfield, California. Inland Crop Dusters, Inc., was operating the helicopter under the provisions of 14 CFR Part 137. The commercial pilot, the sole occupant, sustained serious injuries; the helicopter sustained substantial damage. The local aerial application flight departed Shafter-Minter Field Airport, Shafter, California, about 0700. Visual meteorological conditions prevailed, and no flight plan had been filed. In a written statement, the pilot reported that while turning to reposition himself on the spray run he was making, he heard a rattling noise from the aft end of the helicopter. He then lost tail rotor authority and entered a flat spin. The helicopter was only about 150-175 feet above ground level (agl). He rolled off the throttle and lowered the collective. The pilot attempted to make a run-on landing, but the helicopter continued to spin until it impacted terrain. The helicopter incurred damage to the cabin, skids, tail rotor drive system, tail boom, and center section. A Federal Aviation Administration inspector examined the helicopter after the accident. He stated that there was a crack on the left side support tube area of the tail boom, prior to it connecting to the tail rotor assembly. The inboard side of the crack had significant deposits of rust. It was also noted that the cross-over support tube in that area of the frame was missing. The inspector stated that this would have added excessive stress to the structure during turning maneuvers and caused the last spline coupling shaft to disconnect from the tail rotor gear box. A 50-hour maintenance inspection was completed the day before the accident. ## Aircraft - Registration: [N7NB](https://openairdocs.org/aircraft/N7NB), registered now, S/N 7732, built 1970 (OpenAirDocs) - Reported make and model: Bell 47G-4A - Registry model: [Bell 47G-4A](https://openairdocs.org/model/bell-47g-4a) (registry code 1181031) (OpenAirDocs) - Registry engine: [Lycoming VO-540 series](https://openairdocs.org/engine/lycoming-vo-540-series) (registry code 41534, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 7732 - Airframe hours: 9916.2 - Engines: Lycoming VO-540-B1B3 200 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Registered owner: Inland Crop Dusters Inc. - Airworthiness certificate: Special, Restricted (Special) - Last inspection: 100 hour, April 2, 2004 - Departed: KMIT, Shafter, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 41; injuries: serious; commercial; airplane ratings: single-engine land, multi-engine land; medical: class 2, valid medical--no waivers/lim.; last flight review January 15, 2004; seat: left; flight hours: 3,833 total, 1,800 in this make and model, 173 in the last 90 days, 73 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 0° at 0 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 63 °F, dew point 43 °F - Altimeter: 29.93 inHg - Observed at: BFL ## 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 20040403004479A](https://openairdocs.org/incident/20040403004479A), Apr 3, 2004: Bell 47G4A, Shafter, CA, Substantial damage. (-23) During aerial application, the rotorcraft experienced loss of tail rotor authority. Further investigation revealed that all hangar bearings,… ## Other investigations on N7NB (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 LAX82DVA05](https://openairdocs.org/ntsb/LAX82DVA05), Oct 16, 1981: Bell 47G-4A (N7NB), Wasco, CA, substantial damage 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.