# NTSB CEN13IA387: Martin Charles A Zenith Stol CH 750, N699TX, Paragould, AR, June 28, 2013 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: June 28, 2013, 11:00 local (16:00 UTC) - Place: Paragould, AR - Coordinates: 36.063888, -90.509162 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.0639&lon=-90.5092&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-climb to cruise: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report August 7, 2014 - Report: Approved by Office Director - NTSB office: Central Region - NTSB case key (mKey): 87362 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN13IA387 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/87362/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=87362 - Page: https://openairdocs.org/ntsb/CEN13IA387 ## Probable cause The improper installation of the propeller flange, which resulted in an in-flight separation of the propeller assembly. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Propeller system: propeller assembly](https://openairdocs.org/ntsb-findings/01046110): Aircraft › Aircraft propeller/rotor · Incorrect service/maintenance (probable cause); cases with it: [Martin Charles A ZENITH STOL CH 750, 1 case](https://openairdocs.org/ntsb-findings/01046110/cases.md?model=05630JX), [All aircraft, 29 cases](https://openairdocs.org/ntsb-findings/01046110/cases.md) - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Other (probable cause); cases with it: [Martin Charles A ZENITH STOL CH 750, 1 case](https://openairdocs.org/ntsb-findings/02062035/cases.md?model=05630JX), [All aircraft, 371 cases](https://openairdocs.org/ntsb-findings/02062035/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-climb to cruise: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) (defining event); cases with it: [Martin Charles A ZENITH STOL CH 750, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=05630JX), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) - [Emergency descent: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Martin Charles A ZENITH STOL CH 750, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=05630JX), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis The pilot reported that, during the climb after takeoff, the engine "developed an immediate and heavy vibration." The intensity of the vibration increased, and the pilot was considering shutting the engine down when the vibration abruptly ceased. Looking out the windshield, he observed that the propeller had separated from the airplane. The pilot subsequently executed a forced landing to a field. Metallurgical examination determined that the propeller separation was initiated by a fatigue failure of two propeller flange-to-engine crankshaft flange attachment bolts. Further examination revealed that an incorrect thread lock compound was used on the propeller bolts, and the presence of a second compound suggested that the bolts were not properly cleaned before installation. In addition, washers used in the installation did not correspond with the washers specified by the manufacturer. Finally, extensive fretting damage to the propeller and crankshaft flanges in conjunction with the limited number of flight hours indicated that the attachment bolts were not torqued sufficiently at the time of installation. Available maintenance records did not include any entry noting that the propeller assembly had been removed since the initial installation. ## Factual narrative On June 28, 2013, about 1100 central daylight time, an experimental, amateur-built Martin Zenith STOL CH 750 airplane, N699TX, sustained minor damage during a forced landing after the propeller assembly separated from the engine crankshaft near Paragould, Arkansas. The pilot was not injured. The airplane was registered to a private individual and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight originated from the Kirk Field Airport (PGR), Paragould, Arkansas, about 1050. The ultimate destination was the Grosse Ile Municipal Airport (ONZ), Detroit/Grosse Ile, Michigan. The pilot reported that during the climb out after takeoff, about 5 miles northeast of the airport, the engine "developed an immediate and heavy vibration." He altered course to return to the airport. The intensity of the vibration increased to the level that the pilot considered shutting the engine down, when the vibration abruptly ceased. Looking out the windshield, he observed that the propeller had separated from the airplane. The pilot subsequently executed a forced landing to a field with no additional damage to the airplane. A postaccident examination of the airplane revealed that the propeller flange-to-engine crankshaft flange attachment bolts had failed. The mating surfaces of the propeller and crankshaft flanges exhibited fretting damage. Portions of five of the six bolts remained with the crankshaft flange; one bolt had separated and was not recovered. Metallurgical examination revealed that two bolt fragments exhibited features consistent with fatigue fracture. The remaining three recovered bolt fragments exhibited features consistent with overstress fracture. Damage was observed to the threads on three of the crankshaft flange bolt holes, including the bolt that had separated completely. Deposits consistent with thread lock were observed on the threads of the bolt fragments and the bolt holes in the crankshaft flange. The thread lock material appeared red in color; in addition, a substance that appeared to be yellow in color was observed between the red thread lock and the thread flank. Washers recovered with the propeller exhibited 12 radially-oriented step features on one face and 40 radially-oriented step features on the opposite face consistent with a disk-type lock washer. Impressions corresponding to the washer steps were observed adjacent to the attachment holes on the propeller flange and the clamping face of two bolt heads. The propeller flange also exhibited contact marks consistent with the edge of a larger spring or cone-shaped washer. The engine manufacturer's documentation noted that the standard washer for propeller flange installation was to be a Belleville (cone or spring) washer. The accident airplane was equipped with a 120-horsepower, six-cylinder, Jabiru model 3300 reciprocatingengine. The operator reported that the airframe and engine had accumulated about 32 hours at the time of the accident, with 6 hours since the most recent inspection. Copies of the airframe and engine maintenance logbooks were provided to the National Transportation Safety Board (NTSB). The engine logbook copies included a single maintenance entry dated June 17, 2013. It noted the completion of a 100-hour inspection at an airframe/engine time of 15.2 hours. There were no subsequent entries. In July 2008, the engine manufacturer issued a service bulletin informing pilots and mechanics of several incidents in which the propeller and engine crankshaft flanges had separated. The bulletin noted that the cases had involved the improper installation of the propeller. The bulletin advised operators that if the propeller was not installed properly, it should be refitted to the correct procedure. It noted that the bolt and crankshaft threads should be cleaned to remove any remaining thread lock compound. In addition, the use of Loctite 620 was required because of its high temperature tolerance. Loctite 620 was green in color. ## Aircraft - Registration: [N699TX](https://openairdocs.org/aircraft/N699TX), registered now, S/N 75-8037, built 2012 (OpenAirDocs) - Reported make and model: MARTIN CHARLES A ZENITH STOL CH 750 - Registry model: [Martin Charles A ZENITH STOL CH 750](https://openairdocs.org/model/martin-charles-a-zenith-stol-ch-750) (registry code 05630JX) (OpenAirDocs) - Registry engine: [Jabiru 3300A](https://openairdocs.org/engine/jabiru-3300a) (registry code 34804, 4 cycle) (OpenAirDocs) - Category: Airplane - Serial number: 75-8037 - Year built: 2012 - Airframe hours: 32 - Engines: Jabiru 3300 120 horsepower reciprocating - Damage: Minor damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, June 27, 2013, 6 hours before - Departed: PGR, Paragould, AR - Destination: ONZ, Grosse Ile, MI - Airport: PGR, Kirk Field ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 65; injuries: none; airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review August 16, 2011; seat: left; flight hours: 11,000 total, 30 in this make and model, 10,700 as pilot in command, 46 in the last 90 days, 15 in the last 30 days, 0 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 330° at 7 knots - Visibility: 20 statute miles - Lowest ceiling: none - Temperature: 81 °F, dew point 70 °F - Altimeter: 30.10 inHg - Observed at: PGR, 2 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). - [Incident 20130628010979I](https://openairdocs.org/incident/20130628010979I), Jun 28, 2013: Martin Charles A ZENITH STOL CH 750, Paragould, AR, Minor damage. On June 28, 2013 at approximately 1100 hours local, a zenith stol CH750 manufactured by [privacy data omitted], registration number N699TX, serial number… ## Docket (5 files) The files NTSB released with the investigation on July 17, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=87362. 5.4 MB in all. - Pilot/Operator Aircraft Accident Report (item 1, .PDF, 2.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414208&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report-Redacted.PDF - Airplane Maintenance Logbook (item 2, .PDF, 840 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414209&FileExtension=.PDF&FileName=Airplane%20Maintenance%20Logbook-Redacted.PDF - Engine Maintenance Logbook (item 3, .PDF, 220 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414210&FileExtension=.PDF&FileName=Engine%20Maintenance%20Logbook-Redacted.PDF - Materials Lab Factual Report (item 4, .PDF, 1.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414211&FileExtension=.PDF&FileName=Materials%20Lab%20Factual%20Report-Master.PDF - Engine Manufacturer Service Bulletin (item 5, .PDF, 412 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414212&FileExtension=.PDF&FileName=Engine%20Manufacturer%20Service%20Bulletin-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.