# NTSB MIA96LA176: Hiller OH-23C, N301CH, Marathon, FL, July 4, 1996 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: July 3, 1996, 20:15 local (Jul 4, 1996, 00:15 UTC) - Place: Marathon, FL - Coordinates: 24.710103, -81.080039 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=24.7101&lon=-81.0800&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 2 minor - Status: Completed, report February 28, 1997 - Report: Approved by Office Director - NTSB case key (mKey): 38044 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=MIA96LA176 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/38044/pdf - Page: https://openairdocs.org/ntsb/MIA96LA176 ## Probable cause Improper repair of a previous crack in the blue main rotor blade by unknown persons; improper inspection of the main rotor blades by maintenance personnel, following a reported vibration problem; and subsequent failure of the main rotor blade, which resulted in an uncontrolled collision with the terrain. ## 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 - rotor system,main rotor blade - previous damage (cause) - rotor system,main rotor blade - cracked (cause) - maintenance,major repair - improper, unknown (cause) - rotor system,main rotor - vibration - maintenance,inspection - inadequate, company maintenance personnel (cause) - rotor system,main rotor blade - failure (cause) - rotor system,main rotor blade - separation - In flight collision with terrain/water, descent - uncontrolled ## Analysis During a previous flight, the helicopter was reported to have excessive vertical vibration and to require excessive collective forces during flight. Mechanics worked on the main rotor blades to correct the problem, then the helicopter was flown on a maintenance test flight. During the test flight, the pilot noted that the vertical vibration had 'gone away,' but before landing, the vertical vibration returned. Shortly thereafter, the pilot heard a loud 'pop'. As he flared for landing, the blue main rotor blade separated and the helicopter crashed. Examination of the separated blade showed the wood in the area of the blade grip had failed, allowing the blade to separate. Evidence of a previous repair was present in this area, which lacked adequate adhesive between some of the mating surfaces. Also, an unapproved sealant had been used over the repaired area, and oil had contaminated the wood in this area. There was no evidence of dry rot in the failed area. The logbook records did not show the previous blade repair. ## Factual narrative On July 3, 1996, about 2015 eastern daylight time, a Hiller OH-23C, N301CH, registered to an individual, lost a main rotor blade and crashed while landing at the Marathon Airport, Marathon, Florida, while on a 14 CFR Part 91 maintenance test flight. Visual meteorological conditions prevailed at the time and no flight was filed. The helicopter received substantial damage and the airline transport-rated pilot and one passenger received minor injuries. The flight originated from the Marathon Airport shortly before the accident. The pilot stated the helicopter had been purchased and trucked from Texas on June 20, 1996, with the main rotor blades removed. A mechanic had reinstalled the main rotor blades on arrival in Marathon, Florida. He began flying the helicopter and experienced a problem with vertical vibration of the main rotor blades over the previous week before the accident. Several mechanics had worked on the main rotor blades and made adjustments to correct the vertical vibration problem. At the time of the accident he was flying with a mechanic who had a balancing device to obtain the inflight balance condition of the main rotor blades. After takeoff, with the mechanic on their third test flight, he remained in the airport traffic pattern for runway 25. While on the downwind leg, the vertical vibration, which had previously gone away, returned. Shortly after it returned he heard a loud "pop" noise. He immediately turned toward the airport. As he was landing a main rotor blade separated and the helicopter crashed to the ground. Postcrash examination of the main rotor blades was performed by FAA and Hiller Aircraft Corporation Engineers. The blue main rotor blade had failed and torn out of the grip plate in a spanwise direction. There was no evidence of dry rot in the wood at the blade grip end. There had been repairs made in the wood of the blade grip end of the blade and there was no evidence of adhesive in the repaired area. A material that was not specified for use on the blade was used to seal the repaired area. There was oil contamination in the wood of the blade grip end of the blade. (See attached Hiller Aircraft Report.) Available aircraft logbook records showed the blades were removed from the aircraft and inspected on August 29, 1989, 503 flight hours before the accident. The aircraft received an annual inspection on June 1, 1996, 18 flight hours before the accident. ## Aircraft - Registration: N301CH (not matched to a registry record) - Reported make and model: Hiller OH-23C - Category: Helicopter - Serial number: 56-2252 - Airframe hours: 5222 - Engines: Franklin 6V-335B 210 horsepower reciprocating - Damage: Substantial damage - Flight: Part 91 - Registered owner: Jack Shahan - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 1, 1996, 18 hours before - Departed: MTH - Airport: MTH, Marathon, runway 25, 5,008 × 100 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 38; flight instructor, airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: center; flight hours: 5,961 total, 30 in this make and model, 4,883 as pilot in command, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Dusk - Wind: 180° at 7 knots - Visibility: 7 statute miles - Lowest ceiling: 7,500 ft overcast - Temperature: 81 °F, dew point 72 °F - Altimeter: 29.00 inHg - Observed at: EYW, 1 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 19960703020029A](https://openairdocs.org/incident/19960703020029A), Jul 3, 1996: Hiller OH23G, Marathon, FL, Substantial damage. (.4)During a previous flight, the helicopter was reported to have excessive vertical vibration and to require excessive collective forces during flight.… 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.