# NTSB FTW98LA234: Harding Revolution MINI-500B, N6144S, Grove, OK, May 20, 1998 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: May 20, 1998, 09:25 local (14:25 UTC) - Place: Grove, OK - Coordinates: 36.589397, -94.779762 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.5894&lon=-94.7798&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed, report December 1, 1999 - Report: Approved by Office Director - NTSB case key (mKey): 20619 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW98LA234 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/20619/pdf - Page: https://openairdocs.org/ntsb/FTW98LA234 ## Probable cause The improper alignment of the main drive belt by the owner/pilot/mechanic, which resulted in the failure of the main drive belt. A factor was the lack of suitable terrain for the forced landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, cruise - rotor drive system,main rotor drive belt - failure (cause) - maintenance,alignment - improper, owner/pilot mechanic (cause) - Forced landing, descent - emergency - autorotation - initiated, pilot in command - In flight collision with object, descent - emergency - object - vehicle - terrain condition - none suitable (contributing factor) - In flight collision with terrain/water, descent - uncontrolled ## Analysis While cruising at an altitude of 1,350 feet MSL, the pilot felt a 'sudden hesitation and [smelled the] odor of smoke.' While 'determining if [a] serious malfunction existed,' the helicopter experienced a loss of main rotor drive and altitude, 'along with a stronger burning odor.' The pilot initiated an autorotation to a field adjacent to a school. However, prior to reaching the intended landing area, the helicopter struck a pickup truck, 'flipped over, landed in [the] field and started on fire.' The pilot reported that prior to the flight he had adjusted the alignment of the main drive belt and engine. ## Factual narrative On May 20, 1998, at 0925 central daylight time, a Harding Revolution Mini-500B experimental homebuilt helicopter, N6144S, owned and operated by the pilot, was destroyed during a forced landing following the loss of the main rotor drive near Grove, Oklahoma. Visual meteorological conditions prevailed, and a flight plan was not filed for the Title 14 CFR Part 91 personal flight. The private pilot, sole occupant of the aircraft, sustained minor injuries. The flight originated from the Grove Municipal Airport, about 25 minutes before the accident. The pilot reported that he had adjusted the alignment of the main drive belt and engine. During the ensuing personal/test flight of the helicopter, while at a cruising altitude of 1,350 feet MSL, he felt a "sudden hesitation and [smelled the] odor of smoke." While he was "determining if [a] serious malfunction existed," the helicopter experienced a loss of main rotor drive and altitude, "along with a stronger burning odor." The pilot initiated an autorotation to a field adjacent to a school. However, prior to reaching the intended landing area, the helicopter struck a parked pickup truck, "flipped over, landed in [the] field and started on fire." The helicopter was destroyed by the postimpact fire. The pilot had accumulated a total of 59 flight hours in helicopters, of which 14 hours were accumulated in his homebuilt helicopter. ## Aircraft - Registration: [N6144S](https://openairdocs.org/deregistered/N6144S-2000-02-01), registration cancelled 2000-02-01, S/N 0426 (OpenAirDocs) - Reported make and model: Harding REVOLUTION MINI-500B (REVOLUTION) - Registry model: [Harding Roy A REVOLUTION MINI-500B](https://openairdocs.org/model/harding-roy-a-revolution-mini-500b) (registry code 05605U4) (OpenAirDocs) - Category: Helicopter, amateur-built - Serial number: 0426 - Airframe hours: 14 - Engines: Rotax 582-UL-DCDI 67 horsepower reciprocating - Damage: Destroyed - Fire: On-Ground - Flight: Personal, Part 91 - Registered owner: Roy A. Harding - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Annual, May 20, 1998, 14 hours before - Departed: 1H7 ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 36; private; medical: class 3, valid medical--no waivers/lim.; seat: center; flight hours: 59 total, 14 in this make and model, 59 as pilot in command, 14 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 7 knots - Visibility: 5 statute miles - Lowest ceiling: none - Temperature: 75 °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 19980520010289A](https://openairdocs.org/incident/19980520010289A), May 20, 1998: Amtr MINI500, Grove, OK, Destroyed. Clutch or drive belt failed. Autoratated into parking lot. Struck a truck burned.(.4) while cruising at an altitude of 1,350 feet MSL, the pilot felt a `sudden… 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.