# NTSB BFO93LA149: Lach Bensen B-8M, N8447, Fall River, MA, September 2, 1993 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: September 2, 1993, 08:30 local (12:30 UTC) - Place: Fall River, MA - Location: 41.7015° N, 71.1550° W: Placed by OpenAirDocs: center of Fall River, MA, within about 6 miles (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=41.7015&lon=-71.1550&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious - Status: Completed, report June 30, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 8798 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=BFO93LA149 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/8798/pdf - Page: https://openairdocs.org/ntsb/BFO93LA149 ## Probable cause FATIGUE FAILURE OF THE GYROCOPTER'S MAIN ROTOR CONTROL ARM. fACTORS RELATED TO THE ACCIDENT WERE: A LOOSE CLAMP ON THE ROTOR CONTROL ARM, DUE TO INADEQUATE MAINTENANCE OR INSPECTION, WHICH RESULTED IN CHAFING OF THE CONTROL ARM. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, landing - flare/touchdown - maintenance,inspection - inadequate, company/operator management (contributing factor) - rotorcraft flight control - loose (contributing factor) - rotorcraft flight control - chafed (contributing factor) - rotorcraft flight control - fatigue (cause) - Loss of control - in flight, landing - flare/touchdown - In flight collision with terrain/water, landing ## Analysis AS THE PILOT WAS FLARING TO LAND, THE ROTOR CONTROL ARM (CONTROL STICK) FAILED AT A LOCATION JUST ABOVE THE PILOT'S HEAD. THE GYROCOPTER THEN ROLLED OVER AND CRASHED. A METALLURGICAL EXAMINATION REVEALED THE CONTROL ARM HAD FAILED FROM FATIGUE. THE FATIGUE ORIGINATED WHERE THE CONTROL ARM HAD BEEN CHAFED BY A LOOSE CLAMP. ## Factual narrative On Thursday, September 2, 1993, at about 0830 EDT, a Lach Bensen B-8M, N8447, owned and operated by Walter Lach of Fall River, Massachusetts, rolled over and crashed during a landing at the Fall River Municipal Airport. The gyrocopter was substantially damaged. The pilot, who was the sole occupant, was seriously injured. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight was conducted in accordance with 14 CFR 91. The pilot reported that as he was flaring to land, the rotor control arm (control stick) failed. The gyrocopter then went out of control, the engine RPM began increasing, and the gyrocopter roller over and crashed. A post-accident examination of the gyrocopter revealed the control arm had failed in an area above the pilot's head. The fracture was 90 degrees to the longitudinal axis of the control arm. An examination of the rotor control arm revealed that it had been manufactured from unalloyed aluminum tubing. The tubing was about one inch in diameter with a wall thickness of about 1/16 inch. Hardness of the tubing averaged 84.2 HRF, which was consistent with unalloyed aluminum. Metallurgical examination of the rotor control arm revealed that it had failed from fatigue. Fatigue had originated in two areas on the outer diameter of the control arm, where it had been chafed by a loose clamp. Fatigue had progressed through the wall thickness of the control arm, then it continued circumferentially in both directions. The fatigue crack had progress about half way around the tube before final overstress failure occurred. ## Aircraft - Registration: [N8447](https://openairdocs.org/deregistered/N8447-2013-05-14), registration cancelled 2013-05-14, S/N 1122, built 1974 (OpenAirDocs) - Reported make and model: LACH BENSEN B-8M (BENSEN B-8) - Registry model: [Lach BENSEN B-8M](https://openairdocs.org/model/lach-bensen-b-8m) (registry code 1302110) (OpenAirDocs) - Registry engine: [Continental A&C65 series](https://openairdocs.org/engine/continental-a-c65-series) (registry code 17003, reciprocating) (OpenAirDocs) - Category: Gyroplane, amateur-built - Serial number: 1122 - Airframe hours: 617 - Engines: CONTINENTAL C-65 65 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Walter Lach - Registered owner: Walter Lach - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Annual, March 9, 1993, 5 hours before - Airport: FLR, Fall River Muni, runway 6, 3,950 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 76; private; medical: class 3, valid medical--w/ waivers/lim; seat: center; flight hours: 617 total, 617 in this make and model, 14 in the last 90 days, 5 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Visibility: 100 statute miles - Lowest ceiling: none - Temperature: 70 °F ## 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 19930902032819A](https://openairdocs.org/incident/19930902032819A), Sep 2, 1993: Amtr B8M, Fall River, MA, Substantial damage. During landing flare gyrocopter went out of control. Rolled over. Rotor control arm had failed from fatigue. ## Other investigations on N8447 (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 CHI79FEE72](https://openairdocs.org/ntsb/CHI79FEE72-134979), Jul 20, 1979: Lach/Bensen B8M (N8447), Rockford, IL, 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.