# NTSB WPR12LA096: Arrow Falcon Exporters OH-58A, N902SF, Brawley, CA, January 21, 2012 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: January 20, 2012, 19:00 local (Jan 21, 2012, 03:00 UTC) - Place: Brawley, CA - Coordinates: 32.993057, -115.516944 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=32.9931&lon=-115.5169&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report October 15, 2012 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: FAA FSDO - ADs cited in the narratives: [AD 2012-14-11](https://openairdocs.org/ad/2012-14-11) (OpenAirDocs) - NTSB case key (mKey): 82854 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR12LA096 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/82854/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=82854 - Page: https://openairdocs.org/ntsb/WPR12LA096 ## Probable cause The failure of the main rotor mast due to fatigue cracks that originated from corrosion pits. Contributing to the accident was the operator’s failure to adhere to the manufacturer’s recommended overhaul interval for the main rotor mast. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Main rotor system: main rotor mast/swashplate](https://openairdocs.org/ntsb-findings/01046230): Aircraft › Aircraft propeller/rotor · Failure (probable cause); cases with it: [Bell OH-58A, 1 case](https://openairdocs.org/ntsb-findings/01046230/cases.md?model=1181579), [All aircraft, 13 cases](https://openairdocs.org/ntsb-findings/01046230/cases.md) - [Main rotor system: main rotor mast/swashplate](https://openairdocs.org/ntsb-findings/01046230): Aircraft › Aircraft propeller/rotor · Fatigue/wear/corrosion (probable cause); cases with it: [Bell OH-58A, 1 case](https://openairdocs.org/ntsb-findings/01046230/cases.md?model=1181579), [All aircraft, 13 cases](https://openairdocs.org/ntsb-findings/01046230/cases.md) - [Aircraft](https://openairdocs.org/ntsb-findings/01040000): Aircraft › Aircraft propeller/rotor · Incorrect service/maintenance (probable cause); cases with it: [Bell OH-58A, 1 case](https://openairdocs.org/ntsb-findings/01040000/cases.md?model=1181579), [All aircraft, 11 cases](https://openairdocs.org/ntsb-findings/01040000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Takeoff: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) (defining event); cases with it: [Bell OH-58A, 1 case](https://openairdocs.org/ntsb-events/330/sequence.md?model=1181579), [All aircraft, 994 cases](https://openairdocs.org/ntsb-events/330/sequence.md) ## Analysis During takeoff, the pilot pulled up on the collective, and the main rotor mast fractured near the point where it extends from the transmission; the pilot then aborted the takeoff. The fracture was located below the threads for the mast nut and above the bearing journal for the upper mast bearing. Postaccident examination of the fracture surface revealed multiple fatigue cracks that initiated at the outer diameter of the mast and extended through about 50 percent of the mast's cross section. The fatigue initiation areas and the through-the-wall portion of the fatigue were heavily corroded with extensive pitting and dark deposits visible. A dark oily material was found on the mast's outer surface near the fracture, and the mast's surface was severely corroded on both sides of the fracture. Analysis of samples of the dark oily material suggests that it was a mixture of lubricating oil and water. When the mast is installed on the helicopter, the location where the corrosion and fracture occurred is hidden. To fully inspect the area, the mast assembly must be removed from the helicopter and completely disassembled. Maintenance records indicated that the most recent overhaul of the main rotor mast was completed 2,499 hours before the accident, about 99 hours beyond the helicopter manufacturer's recommended time between overhaul of 2,400 hours. The NTSB has previously investigated a similar main rotor mast failure on the same make and model helicopter; in that case, the most recent overhaul of the main rotor mast was completed 1,486 hours before the accident. As a result of these events, in February 2012, the manufacturer issued an alert service bulletin that reduced the main rotor mast overhaul interval from 2,400 hours to 1,200 hours. Additionally, in July 2012, the Federal Aviation Administration issued Airworthiness Directive (AD) 2012-14-11, applicable to Arrow Falcon Exporters, Rotorcraft Development Corporation, and San Joaquin Helicopters model OH-58A, OH-58A+, and OH-58C helicopters. The AD requires operators of those helicopters to, within 30 days, overhaul the helicopters’ main rotor mast assemblies. ## Factual narrative On January 20, 2012, about 1900 Pacific standard time, an Arrow Falcon Exporters, Inc., OH-58A helicopter, N902SF, sustained substantial damage when its main rotor mast fractured during takeoff near Brawley, California. The commercial pilot, the sole occupant, was not injured. Farm Aviation, Inc., was operating the helicopter under the provisions of 14 Code of Federal Regulations Part 137. Night visual meteorological conditions prevailed for the aerial application flight, and no flight plan was filed. The helicopter was departing for a local flight when the accident occurred. The owner of the company stated that the aircraft was performing outlying operations and was operating off the back of a truck. The helicopter had just been refueled and loaded with applicant. When the pilot pulled up on the collective to begin the takeoff, the main rotor mast fractured near the point where the mast extends from the transmission, and the pilot aborted the takeoff. Both pieces of the fractured mast were examined at the National Transportation Safety Board's Materials Laboratory. The fracture was located near the point where the mast extends from the transmission below the threads for the mast nut and above the bearing journal for the upper mast bearing. Multiple fatigue cracks were found that initiated at the outer diameter of the mast. The overall extent of fatigue was estimated to be through about 50 percent of the mast's cross section. The fatigue initiation areas and the through-the-wall portion of the fatigue were heavily corroded with extensive pitting and dark deposits visible. A dark oily material was found on the mast's outer surface in the vicinity of the fracture, and the mast's surface was severely corroded on both sides of the fracture. Fourier-Transform Infrared spectroscopy analysis of samples of the dark oily material suggested that the material was a mixture of lubricating oil and water. When the mast is installed on the helicopter, the location where the corrosion and fracture occured is hidden. To fully inspect the area, the mast assembly must be removed from the helicopter and completely disassembled. The helicopter was initially manufactured by Bell Helicopter as a military aircraft. On December 5, 2003, it was certificated as a civil aircraft in the restricted category with Arrow Falcon Exporters listed as the aircraft manufacturer. Review of the helicopter's maintenance records by a Federal Aviation Administration (FAA) inspector indicated that the mast's most recent 2,400-hour inspection, which included a magnaflux inspection, was completed on February 27, 2007. The mast was installed in another helicopter (N6251G) from March 1, 2007, to October 26, 2011, and accumulated 2,235.4 flight hours during this time. On October 26, 2011, the mast was installed in the accident helicopter, and, at the time of the accident, the mast had accumulated a total of 2,499 flight hours since the overhaul in February 2007. When the mast fractured, it hadbeen operated for 99 hours beyond the manufacturer's recommended overhaul time of 2,400 hours. A similar mast failure on an Arrow Falcon Exporters OH-58C occurred on July 3, 2011, near Brentwood, California (WPR11LA303). In that case, the most recent overhaul of the main rotor mast was completed 1,486 hours before the accident. On February 20, 2012, Arrow Falcon issed Alert Service Bulletin 2012-58-01, which reduced the overhaul interval for the main rotor mast assemblies on its OH-58s from 2,400 to 1,200 hours. On July 23, 2012, the FAA issued Airworthiness Directive (AD) 2012-14-11, applicable to Arrow Falcon Exporters, Rotorcraft Development Corporation, and San Joaquin Helicopters model OH-58A, OH-58A+, and OH-58C helicopters. The AD required, within 30 days, overhaul of the main rotor mast assemblies of these helicopters. The AD also required performance of specific inspections for a crack, pitting, or corrosion in the threaded area of the mast and associated parts. ## Aircraft - Registration: [N902SF](https://openairdocs.org/deregistered/N902SF-2023-03-06), registration cancelled 2023-03-06, S/N 70-15406, built 1970 (OpenAirDocs) - Reported make and model: Arrow Falcon Exporters, Inc. OH-58A - Registry model: [Bell OH-58A](https://openairdocs.org/model/bell-oh-58a) (registry code 1181579) (OpenAirDocs) - Registry engine: [Allison T63 series](https://openairdocs.org/engine/allison-t63-series) (registry code 03031, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 70-15406 - Engines: Allison 250 C20 turbo shaft - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Farm Aviation Inc - Registered owner: Farm Aviation Inc - Airworthiness certificate: Special, Restricted (Special) - Departed: Brawley, CA - Destination: Brawley, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; injuries: none; commercial, private; airplane ratings: single-engine land, multi-engine land; medical: class 2, without waivers/limitations; seat: right ## Weather - Conditions: Visual (VMC), Night - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 59 °F, dew point 34 °F - Altimeter: 29.97 inHg - Observed at: IPL, 10 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 20120121002419A](https://openairdocs.org/incident/20120121002419A), Jan 21, 2012: Bell OH-58A, Brawley, CA, No damage. Aero falcon OH-58 had a rotor mast failure just pior to lift -off of the aircraft, failure was internal of the main rotor transmission no damage to aircraft… ## Other investigations on N902SF (2) 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 WPR22LA032](https://openairdocs.org/ntsb/WPR22LA032), Nov 9, 2021: Bell OH-58A (N902SF), Holtville, CA, substantial damage. Probable cause: The pilot’s failure to maintain helicopter control after becoming spatially disoriented when the helicopter entered low-level haze/fog. - [NTSB LAX08CA054](https://openairdocs.org/ntsb/LAX08CA054), Jan 30, 2008: Bell OH-58A (N902SF), Brawley, CA, substantial damage. Probable cause: The pilot's failure to maintain clearance from obstacles. A factor in the accident was the dark night conditions. ## Docket (4 files) The files NTSB released with the investigation on August 8, 2012, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=82854. 7.8 MB in all. - Materials Laboratory 15 - Factual Report 12-035 (19 images) (item 1, .PDF, 5.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40367428&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Factual%20Report%2012-035%20(19%20images)-Master.PDF - FAA New AD Sheet (item 2, .PDF, 1.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40374357&FileExtension=.PDF&FileName=FAA%20New%20AD%20Sheet-Redacted.PDF - Statement of Party Representatives to NTSB Investigation (item 3, .PDF, 219 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40374356&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.PDF - Arrow Falcon ASB - Main Rotor Mast Revision (item 4, .PDF, 124 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40374358&FileExtension=.PDF&FileName=Arrow%20Falcon%20ASB%20-%20Main%20Rotor%20Mast%20Revision-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.