# NTSB WPR17LA082: OTT 601XL-B, N610TT, The Dalles, OR, March 31, 2017 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: March 31, 2017, 16:55 local (23:55 UTC) - Place: The Dalles, OR - Coordinates: 45.618057, -121.167503 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=45.6181&lon=-121.1675&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-climb to cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: Minor injuries - Injuries: 2 minor - Status: Completed, report December 14, 2017 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 94948 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA082 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/94948/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=94948 - Page: https://openairdocs.org/ntsb/WPR17LA082 ## Probable cause A partial loss of engine power due to the reverse bending fatigue failure of the propeller hub bolts, which resulted from the bolts not fitting tightly into the propeller hub holes. Also causal was the pilot's decision to use improper bolts for this type of installation/operation. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Propeller system: propeller hub section](https://openairdocs.org/ntsb-findings/01046114): Aircraft › Aircraft propeller/rotor · Failure (probable cause); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-findings/01046114/cases.md?model=056314C), [All aircraft, 13 cases](https://openairdocs.org/ntsb-findings/01046114/cases.md) - [Propeller system: propeller hub section](https://openairdocs.org/ntsb-findings/01046114): Aircraft › Aircraft propeller/rotor · Fatigue/wear/corrosion (probable cause); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-findings/01046114/cases.md?model=056314C), [All aircraft, 13 cases](https://openairdocs.org/ntsb-findings/01046114/cases.md) - [Misc hardware](https://openairdocs.org/ntsb-findings/01071400): Aircraft › Fluids/misc hardware · Incorrect use/operation (probable cause); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-findings/01071400/cases.md?model=056314C), [All aircraft, 41 cases](https://openairdocs.org/ntsb-findings/01071400/cases.md) - [Maintenance: modification/alteration](https://openairdocs.org/ntsb-findings/02062030): Personnel issues › Task performance · Pilot; cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-findings/02062030/cases.md?model=056314C), [All aircraft, 69 cases](https://openairdocs.org/ntsb-findings/02062030/cases.md) - [Info processing/decision: decision making/judgment](https://openairdocs.org/ntsb-findings/02041520): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-findings/02041520/cases.md?model=056314C), [All aircraft, 3,098 cases](https://openairdocs.org/ntsb-findings/02041520/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: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-events/342/sequence.md?model=056314C), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Enroute-climb to cruise: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=056314C), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Landing area undershoot](https://openairdocs.org/ntsb-events/370); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-events/370/sequence.md?model=056314C), [All aircraft, 201 cases](https://openairdocs.org/ntsb-events/370/sequence.md) - [Landing: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Louis W OTT 601XL-B, 1 case](https://openairdocs.org/ntsb-events/470/sequence.md?model=056314C), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The commercial pilot, who was also the owner/builder of the experimental amateur-built airplane, reported that, after departure and while climbing through 3,500 ft mean sea level, he heard the engine sound abruptly change and observed a loss of rpm and higher-than-normal exhaust gas temperature readings. The pilot turned back toward the airport and attempted to troubleshoot the problem; however, the airplane continued to produce less power than expected. The pilot established a normal traffic pattern for the runway. After turning to final, the airplane started descending and had insufficient power to reach the runway. The airplane subsequently impacted terrain short of the runway. Postaccident examination of the airplane revealed that all six propeller bolts that held the propeller hub to the drive hub were fractured. Further examination of the bolts revealed that the fracture surfaces all exhibited similar features consistent with reverse bending fatigue, likely from not fitting tightly into the propeller hub holes. The pilot reported that he had converted the engine and that, given its unique conversion, the bolts that were typically used to connect the propeller hub to the drive hub were too short; therefore, he chose to use the bolts that were on the hub at the time of the accident. Given the condition of the bolts and the pilot's statement, it is likely the bolts did not fit tightly in the propeller hub holes, which led to their failure due to reverse bending fatigue. ## Factual narrative On March 31, 2017 about 1655 Pacific daylight time, an OTT 601XL-B airplane, N610TT, the pilot executed a precautionary landing about one mile southeast of the Columbia Gorge Regional/The Dalles Municipal Airport (DLS), The Dalles, Oregon after the engine experienced a partial loss of engine power. The commercial pilot and one passenger sustained minor injuries, and the airplane was substantially damaged throughout. The airplane was registered to and operated by the pilot as a 14 Code of Federal Regulations Part 91 personal, local flight. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The pilot reported that the purpose of the flight was to verify the proper fuel mixture setting for the electronic mixture system. The airplane departed the airport to the northeast and while climbing through 3,500 feet, the pilot heard the engine sound abruptly change. Concurrent with the change, he observed a loss of RPM and high exhaust gas temperature readings. The pilot returned towards the airport and attempted to troubleshoot the problem, however, the airplane was producing less power than expected. The pilot established a normal traffic pattern for runway 31. After turning final the airplane was low, and despite the pilot adding power, the airplane impacted terrain short of the runway surface. A postaccident examination revealed no indications of catastrophic malfunction. The engine was rotated and compression was established on all cylinders. The spark plugs were removed and the cylinders were boroscoped; all cylinders exhibited normal operating signatures. The external timing marks at the rear of the engine were not consistent with the markings on the multi-toothed plate on the propeller shaft. Further examination revealed the bolts holding the propeller hub to the drive hub were all fractured. The bolts were removed and sent to the National Transportation Safety Board (NTSB) materials laboratory for further examination. The NTSB materials laboratory reported that the bolts were fractured in the 13th-15th thread root from the base of the bolt. The general features of the fracture surfaces were consistent with each other. The fracture surfaces exhibited opposite-facing flat thumbnail-shaped regions with a middle rougher region. The thumbnail regions exhibited crack arrest marks, which were orientated with propagation inward from the surface of the thread roots. The thumbnail regions also exhibited ratchet marks near the thread root surfaces, consistent with multiple crack initiation sites. These features were all consistent with fatigue in reverse bending. The pilot reported that the engine was a Corvair conversion engine built by him and a friend. They built this engine to be slightly different than other conversions, which allows it to be more powerful. The bolts that are normally used to connect the propeller hub to the drive hub were too short; therefore, he elected to use the accident bolts. Hefurther reported that he believes he torqued the bolts properly, however, he noted that the holes on the propeller hub were not very tight. ## Aircraft - Registration: [N610TT](https://openairdocs.org/deregistered/N610TT-2017-08-14), registration cancelled 2017-08-14, S/N 6-7884, built 2012 (OpenAirDocs) - Reported make and model: OTT 601XL-B - Registry model: [Louis W OTT 601XL-B](https://openairdocs.org/model/louis-w-ott-601xl-b) (registry code 056314C) (OpenAirDocs) - Registry engine: [Aeromax 100 IFB](https://openairdocs.org/engine/aeromax-100-ifb) (registry code 00550, reciprocating) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 6-7884 - Year built: 2012 - Airframe hours: 129 - Engines: OTT 3250 125 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, June 14, 2016, 33 hours before - Departed: DLS, The Dalles, OR - Destination: DLS, The Dalles, OR - Airport: DLS, Columbia Gorge Regional/The Da - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 76; injuries: minor; commercial; airplane ratings: single-engine land; last flight review September 28, 2016; seat: left; restraint: 3-point; flight hours: 1,661 total, 129 in this make and model, 1,600 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 330° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 64 °F, dew point 36 °F - Altimeter: 30.20 inHg - Observed at: DLS, 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 20170331003129A](https://openairdocs.org/incident/20170331003129A), Mar 31, 2017: Louis W Ott 601XL-B, The Dalles, OR, Substantial damage. The aircraft was climbing through 3500 feet when the engine experienced a loss of power and decrease in RPM of approximately 200. The pilot elected to return… ## Docket (4 files) The files NTSB released with the investigation on October 24, 2017, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=94948. 4.5 MB in all. - Materials Laboratory Factual Report (item 1, .PDF, 2.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40457286&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 2, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40457287&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Engine Examination Observations - Courtesy of the Federal Aviation Administration (item 3, .PDF, 282 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40457288&FileExtension=.PDF&FileName=Engine%20Examination%20Observations%20-%20Courtesy%20of%20the%20Federal%20Aviation%20Administration-Master.PDF - Evidence Control Form - Propeller Hub Bolts (item 4, .PDF, 808 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40457289&FileExtension=.PDF&FileName=Evidence%20Control%20Form%20-%20Propeller%20Hub%20Bolts-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.