# NTSB LAX00LA173: Rotorway Exec 162F, N21901, Chandler, AZ, April 6, 2000 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: April 6, 2000, 08:00 local (15:00 UTC) - Place: Chandler, AZ - Coordinates: 33.270927, -111.939704 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.2709&lon=-111.9397&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report November 1, 2001 - Report: Approved by Office Director - NTSB case key (mKey): 49069 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX00LA173 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/49069/pdf - Page: https://openairdocs.org/ntsb/LAX00LA173 ## Probable cause The inadequate maintenance inspection of the secondary shaft which resulted in its fatigue failure that emanated from a corroded circumferential score mark. A factor was the fence that the pilot flared to avoid, resulting in a hard landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, approach - vfr pattern - downwind - rotor drive system,engine to transmission drive - failure,total (cause) - rotor drive system,tail rotor drive shaft - fatigue (cause) - maintenance,inspection - inadequate, kit manufacturer (cause) - Loss of engine power(total) - mech failure/malf, approach - vfr pattern - downwind - autorotation - performed, pilot in command - Hard landing, descent - emergency - object - fence (contributing factor) ## Analysis The helicopter landed hard collapsing the left skid and resulting in the main rotor blades striking the tail boom. While in the traffic pattern, during the downwind leg, the pilot heard a loud noise from the rear of the helicopter. He entered an autorotation and checked the cockpit instruments. Noting no anomalies, he rolled on the throttle and discovered that the engine speed would increase but the rotor speed would not. The pilot flared to avoid a fence then landed hard. Subsequent examination of the engine secondary shaft that transmits power to the main rotor through drive belts revealed that the shaft had failed in fatigue. There were numerous longitudinal and circumferential score marks on the secondary shaft indicating removal and reinstallation of the shaft many times. The fatigue fracture originated at one of the circumferential score marks and exhibited oxidation, indicating it had been fractured for some time. ## Factual narrative On April 6, 2000, at 0800 hours mountain standard time, a homebuilt Rotorway Exec 162F, N21901, sustained substantial damage when the main rotor blades contacted the tail boom during an autorotation near the Memorial Airport, Chandler, Arizona. The helicopter was being operated by Rotorway International under the provisions of 14 CFR Part 91. The certified flight instructor and student pilot were not injured. The local area instructional flight originated at the Stellar Air Park near Chandler at an unknown time. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that while at 300 feet agl on a downwind traffic pattern leg, they heard a loud noise from the rear of the helicopter. He immediately entered an autorotative descent. During the descent, he checked the cockpit gauges and found no discrepancies. He decided to roll the throttle back on. The pilot stated that the engine rpm increased, but not the rotor rpm; the needles were not coupled. There was a barbed wire fence in their flight path, so the pilot extended the glide, flared, and landed hard. The left landing gear skid collapsed and the main rotor blades struck the tail boom. The helicopter secondary shaft that transmits power from the engine to the main rotor, the water pump, the fan, the tail rotor, and the lower fan was examined in the Safety Board's Materials Laboratory in Washington, DC. There were many light scratches longitudinal to the shaft axis and numerous short circumferential score marks and light scratches observed on the surface of the secondary shaft. The shaft was in two sections and exhibited a fracture surface that was on a flat transverse plane that contained multiple crack arrest positions, typical of fatigue cracking. About 20 percent of the fracture surface adjacent to the origin area contained a rust-colored discoloration. The edge of the fracture face had been mechanically damaged which had obliterated the fracture surface details directly adjacent to the origin area. The band of circumferential marks on the shaft surface was measured, adjacent to the initiation site, and was found to be 0.16 inches wide. Measurement adjacent to the initiation site showed that the first circumferential score mark was 0.09 inches from the fracture face. ## Aircraft - Registration: [N21901](https://openairdocs.org/deregistered/N21901-2003-11-12), registration cancelled 2003-11-12, S/N RI6035, built 1995 (OpenAirDocs) - Reported make and model: Rotorway EXEC 162F - Registry model: [Cobb Intl Inc/DBA Rotorway INT EXEC 162F](https://openairdocs.org/model/cobb-intl-inc-dba-rotorway-int-exec-162f) (registry code 05625SN) (OpenAirDocs) - Registry engine: [Amateur-built UNKNOWN ENG](https://openairdocs.org/engine/amateur-built-unknown-eng) (registry code 99999) (OpenAirDocs) - Category: Helicopter, amateur-built - Serial number: RI6035 - Airframe hours: 1200 - Engines: Rotorway 162F 150 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Registered owner: Cobb International - Airworthiness certificate: Special, Experimental (Special) - Last inspection: 100 hour, April 3, 2000, 8 hours before - Departed: P19, AZ - Airport: Memorial, runway 12, 8,500 × ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 28; private, flight instructor, commercial; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 598 total, 95 in this make and model, 506 as pilot in command, 62 in the last 90 days, 30 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 80° at 6 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 154 °F, dew point 97 °F - Altimeter: 29.00 inHg - Observed at: PHX, 13 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 20000406005829A](https://openairdocs.org/incident/20000406005829A), Apr 6, 2000: Amtr EXEC162F, Chandler, AZ, Substantial damage. (-23) On departure from memorial field, chanler, Arizona, pilot climbed pattern altitude of 300 ft (AGL). A loud noise was heard form rear of helicopter and… ## Other investigations on N21901 (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 LAX02LA121](https://openairdocs.org/ntsb/LAX02LA121), Apr 1, 2002: Rotorway Exec 165F (N21901), Chandler, AZ, substantial damage. Probable cause: The tail rotor drive system failure as a result of incorrect installation procedures by the manufacturer's personnel. 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.