# NTSB WPR13LA304: Dorman Bakeng, N39796, Garden Valley, ID, July 2, 2013 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 2, 2013, 08:00 local (14:00 UTC) - Place: Garden Valley, ID - Coordinates: 44.066944, -115.931114 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=44.0669&lon=-115.9311&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-climb to cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report August 25, 2015 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: FAA FSDO - NTSB case key (mKey): 87365 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR13LA304 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/87365/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=87365 - Page: https://openairdocs.org/ntsb/WPR13LA304 ## Probable cause A mechanical failure of the oil cooler, which resulted in a complete loss of oil and engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Eng oil sys (airframe furnish): cooler](https://openairdocs.org/ntsb-findings/01057921): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Dorman Donald Thoresen BAKENG DUCE, 1 case](https://openairdocs.org/ntsb-findings/01057921/cases.md?model=05604R9), [All aircraft, 7 cases](https://openairdocs.org/ntsb-findings/01057921/cases.md) - [Fluids: oil](https://openairdocs.org/ntsb-findings/01071020): Aircraft › Fluids/misc hardware · Fluid level (probable cause); cases with it: [Dorman Donald Thoresen BAKENG DUCE, 1 case](https://openairdocs.org/ntsb-findings/01071020/cases.md?model=05604R9), [All aircraft, 174 cases](https://openairdocs.org/ntsb-findings/01071020/cases.md) - [Engine (reciprocating): recip eng oil sys](https://openairdocs.org/ntsb-findings/01058550): Aircraft › Aircraft power plant · Damaged/degraded (probable cause); cases with it: [Dorman Donald Thoresen BAKENG DUCE, 1 case](https://openairdocs.org/ntsb-findings/01058550/cases.md?model=05604R9), [All aircraft, 130 cases](https://openairdocs.org/ntsb-findings/01058550/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: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340); cases with it: [Dorman Donald Thoresen BAKENG DUCE, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=05604R9), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Enroute-climb to cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Dorman Donald Thoresen BAKENG DUCE, 1 case](https://openairdocs.org/ntsb-events/341/sequence.md?model=05604R9), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Enroute-climb to cruise: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Dorman Donald Thoresen BAKENG DUCE, 1 case](https://openairdocs.org/ntsb-events/440/sequence.md?model=05604R9), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis In the days just preceding the accident, the owner-pilot made several uneventful flights in the experimental amateur-built airplane, which was equipped with an aircraft engine and an automotive performance/racing oil cooler. On the morning of the accident, the owner's brother joined him at a remote turf airstrip in mountainous terrain to conduct a flight. The brother, who was also a pilot, took the aft cockpit seat, which was the primary pilot position in the airplane. The owner took the forward cockpit seat. The brother conducted the engine start, taxi-out, run-up, and takeoff, which were all normal. During the climbout, the owner realized that the airplane was not performing as it should, and, when he asked his brother about it, his brother reported that the engine was losing power. The owner took control of the airplane and began a turnback to the airport, and the engine lost total power shortly thereafter. An attempt to restart the engine was unsuccessful, and the airplane landed short of the runway. Examination of the airport revealed an oil spray trail on the turf that began at the parking location and extended along the taxi route and through the takeoff path. Postaccident examination of the airplane revealed a significant oil streak on the exterior side of the airplane that emanated from the oil cooler. The engine was also devoid of oil. Detailed examination of the oil cooler revealed deformation of its containment frame and damage to some of the unit's oil tubes, which included separation of the cooling fins from the tubes and several holes in the tubes that permitted oil to escape the cooler. The damage signatures were not consistent with preaccident or postaccident impact or other structural deformation damage. The damage signatures were somewhat, but not completely, consistent with an internal overpressure of the oil cooler; however, the reasons for the internal overpressure could not be determined during postaccident examination. ## Factual narrative Oil Cooler The oil cooler was installed in an aluminum airbox that was mounted just forward of the lower left portion of the firewall. A scat tube routed ram air into the airbox to effect cooling of the oil. The oil cooler was an Earls Performance brand Model 21608 automotive performance/racing unit, constructed of aluminum. According to information provided by the manufacturer, each unit was pressure-tested to 175 psi. The time in service of the oil cooler was not determined. The cooler configuration was similar to typical aircraft engine oil coolers. The cooler had an input and output plenum, each with a threaded fitting for its respective oil line. The two plenums were on opposite ends of the unit, and connected by 16 flat tubes that were perpendicular to the plenums, and parallel to one another. The tubes transported oil from the input plenum to the output plenum on the other side of the unit. The 16 tubes were interconnected via 15 rows of fins, which transferred the heat from the oil to the ram air passing through the cooler. As installed in the airplane, the cooler was oriented so that the two plenums were at the top and bottom, and extended laterally. The tubes were oriented near-vertically, and for the investigation, were numbered from 1 to 16, inboard to outboard. The inlet and outlet fittings were located on the inboard side of the unit. A riveted set of four aluminum caps formed a structural frame for the cooler. The inboard and outboard caps were captive between the top and bottom caps; each corner joint was attached by two rivets. One fitting was wrapped with red tape as a marker for the investigation. The fitting with the red marker tape was the lower (or bottom) fitting. It was not determined whether this was the input or output line fitting. Laboratory examination of the oil cooler did not reveal any residue or staining from oil leakage on any of its surfaces, with the exception of some dirt deposits around the fittings. Overall the oil cooler had a clean appearance. No evidence of impact or other contact damage was observed on any part of the oil cooler. The oil cooler exhibited some plastic deformation, particularly between tubes 5 to 8, and tubes 12 to 13. The area of deformation bounded by tubes 5 to 8 was visible on the forward and aft faces of the cooler, while the deformation between tubes 12 and 13 was only visible on the aft face. The deformation was consistent with loading in the inboard-outboard direction, perpendicular to the tubes. The deformation of the tubes caused portions of the cooling fins to separate from the tubes, breaking the brazed connections between the fins and tubes. Between tubes 6 and 7, some areas where the fins were separated from the tubes resulted in small holes in those tubes. The eight rivets in the four cap corner joints exhibited varying degrees of pull-through, consistent with tensile overload. One rivet was completely pulled through, six were partially pulled through, and one was onlyslightly deformed. The direction of the loading was inboard-outboard, perpendicular to the tubes. The tube and frame damage was not consistent with any pre- or post-impact damage or structural deformation, and the surrounding airbox was intact. The tube and frame damage was somewhat consistent with a cooler internal overpressure condition. The investigation did determine the timing or failure mechanism for the cooler damage. The investigation did not examine test the oil pressure relief valve. According to FAA records, the airplane was manufactured in 1997. Neither the current owner nor his brother was the builder of the airplane; the current owner had purchased the airplane about 1 year prior to the accident. The airplane was of the high parasol-wing taildragger configuration, with tandem open cockpits. The airplane was equipped with a Lycoming O-320-B2D engine, serial number L-21662-27A, and a fixed-pitch two blade propeller. The engine utilized a pressure-type wet sump lubrication system. Oil sump capacity was 8 quarts, and minimum engine operating oil quantity was 2 quarts. The owner reported that the sump contained about 5.5 quarts at the time of his pre-flight inspection. Normal operating oil pressure range was 60 to 90 psi. The engine was equipped with an oil pressure relief valve to maintain oil pressure within the manufacturer-specified limits. The aft cockpit was equipped with an oil temperature and pressure gauge. The investigation did not determine whether oil and temperature information was presented in the forward cockpit. According to information provided by the owner, the most recent annual condition inspection was completed on June 28, 2013. The maintenance entry for that inspection reported the following times: "Hobbs 395.4," TTE 1598.1," TSMOH 407.9," and "TTP 006.7." The engine had accumulated about 4 hours since its most recent inspection. According to FAA information, the runway at U88 was turf, with a length of 3,850 feet, and an elevation of 3,177 feet. On July 2, 2013, about 0800 mountain daylight time, an experimental amateur-built Bakeng Deuce airplane, N39796, was substantially damaged when it impacted vegetation and terrain near Garden Valley airport (U88), Garden Valley, Idaho, following a complete loss of engine power shortly after takeoff. The owner/pilot and his passenger were not injured. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the flight. According to the owner-pilot, he based the airplane at Salt Lake City International airport (SLC), and had flown to U88 several times previously. On the accident trip, he originally left SLC for U88 on Saturday, June 29, stopped once for fuel, and landed at U88 later that same day. On Sunday June 30 he flew to another airport in Idaho, where he and the airplane remained overnight, before returning to U88 on Monday morning. Later that day,he made an out and back flight from U88 to obtain fuel. All flights were uneventful, and during preflight inspections, the engine oil quantity remained at its normal value. On the morning of the accident, the owner's brother, who was also a pilot, joined him for a planned flight. The preflight inspection was normal. The airplane was equipped with dual flight and engine controls. The brother took the rear cockpit, which was the primary pilot position for the airplane. The brother conducted the engine start, taxi out, and runup; all were normal. The brother performed the takeoff from runway 28. When the airplane was on the crosswind leg, the owner queried his brother why they weren't climbing as well as he expected, and the brother responded that he was "losing rpms." The owner took control of the airplane, and turned back towards the airport. When the airplane was about 750 feet above the ground, the engine ceased operating. Since the engine could not be started from the front seat, the owner asked the brother to attempt a restart, but attempts were unsuccessful. The owner then attempted to land the airplane on runway 10 (opposite direction of the takeoff), but the airplane struck vegetation and the ground short of the runway. It came to rest upright, about 30 feet short of the runway threshold. The owner reported that the conditions at U88 included clear skies, a temperature of 75 degrees F (24 degrees C) and no wind. Front Cockpit Owner-Pilot Federal Aviation Administration (FAA) records indicated that the owner-pilot held a private pilot certificate, with a single-engine airplane rating. The certificate was issued in February 2010. The owner's most recent flight review was completed, and his most recent FAA third-class medical certificate was issued, in May 2012. The owner reported that he had a total flight experience of about 486 hours, including about 69 hours in the accident airplane make and model. Aft Cockpit Pilot According to information provided by the owner, his brother (the takeoff pilot) held a private pilot certificate, with a single-engine airplane rating. His most recent flight review was completed, and his most recent FAA third-class medical certificate was issued, in May 2012. The owner reported that the takeoff pilot had a total flight experience of about 133 hours, including about 44 hours in the accident airplane make and model. Post accident examination by the owner and an inspector from the FAA revealed an oil streak on the left side of the airplane that extended aft from the cowling. Examination of the airport revealed an oil spray trail on the turf ground surfaces along the taxi-out, run-up, and takeoff path. Examination of the de-cowled engine revealed that no oil remained in the engine, and that the oil streak had emanated from an undetermined location near or on the aft face of the oil cooler, which was mounted just forward of the firewall. Detailed examination of the oil cooler fluid lines,airbox,and mounting didnot reveal any abnormalities, indications of distress or distortion, or failures. Removal of the cover of the airbox revealed that some of the oil cooler tubes and fins were deformed. The cooler was removed and shipped to the NTSB Material Laboratory for detailed examination. ## Aircraft - Registration: [N39796](https://openairdocs.org/deregistered/N39796-2018-02-13), registration cancelled 2018-02-13, S/N 235 (OpenAirDocs) - Reported make and model: DORMAN BAKENG (Deuce) - Registry model: [Dorman Donald Thoresen BAKENG DUCE](https://openairdocs.org/model/dorman-donald-thoresen-bakeng-duce) (registry code 05604R9) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 235 - Year built: 1997 - Engines: Lycoming O-320-B2D 160 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, June 28, 2013, 4 hours before - Departed: U88, Garden Valley, ID - Destination: U88, Garden Valley, ID - Airport: U88, Garden Valley ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 57; injuries: none; private; airplane ratings: single-engine land; medical: class 3, with waivers/limitations; last flight review May 23, 2012; seat: front; restraint: 3-point; flight hours: 486 total, 69 in this make and model, 486 as pilot in command, 10 in the last 90 days, 8 in the last 30 days, 2 in the last 24 hours - Pilot; age 0; injuries: none; private; airplane ratings: single-engine land; medical: class 3, with waivers/limitations; seat: rear; restraint: 3-point; flight hours: 133 total, 44 in this make and model, 80 as pilot in command, 4 in the last 90 days ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 20 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 20130702012169A](https://openairdocs.org/incident/20130702012169A), Jul 2, 2013: Dorman Donald Thoresen BAKENG DUCE, Garden Valley, ID, Substantial damage. On 02 July 2013 at approximately 0800 MDT, an experimental amateur built bakeng deuce aircraft, N79396, piloted by [privacy data omitted], took off from Garden… ## Docket (7 files) The files NTSB released with the investigation on July 22, 2015, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=87365. 8.4 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 3.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40429708&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Record of Conversation - Pilot (item 2, .PDF, 194 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40429709&FileExtension=.PDF&FileName=Record%20of%20Conversation%20-%20Pilot-Master.PDF - Boise County Sheriff’s Office Supplement Report (item 3, .PDF, 349 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40429710&FileExtension=.PDF&FileName=Boise%20County%20Sheriff%E2%80%99s%20Office%20Supplement%20Report-Redacted.PDF - On Scene and Initial Information (item 4, .PDF, 4.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40435676&FileExtension=.PDF&FileName=On%20Scene%20and%20Initial%20Information-Master.PDF - Mechanics Exam Report (item 5, .PDF, 71 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40435677&FileExtension=.PDF&FileName=Mechanics%20Exam%20Report-Redacted.PDF - Materials Laboratory Factual Report (item 6, .PDF, 495 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40435678&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Master.PDF - Oil Cooler Information (item 7, .PDF, 341 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40435679&FileExtension=.PDF&FileName=Oil%20Cooler%20Information-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.