# NTSB CEN16LA302: Sonex Waiex, N12YX, Fond du Lac, WI, August 3, 2016 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: August 3, 2016, 11:55 local (16:55 UTC) - Place: Fond du Lac, WI - Coordinates: 43.770278, -88.501388 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.7703&lon=-88.5014&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: Serious injuries - Injuries: 2 serious - Status: Completed, report March 22, 2018 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Sonex Aircraft LLC, FAA FSDO - NTSB case key (mKey): 93754 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN16LA302 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/93754/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=93754 - Page: https://openairdocs.org/ntsb/CEN16LA302 ## Probable cause A partial loss of engine for reasons that could not be determined during an examination of the engine. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Sonex WAIEX, 1 case](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=05615ME), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md) - [Object/animal/substance: wire](https://openairdocs.org/ntsb-findings/03022032): Environmental issues › Physical environment · Contributed to outcome; cases with it: [Sonex WAIEX, 1 case](https://openairdocs.org/ntsb-findings/03022032/cases.md?model=05615ME), [All aircraft, 588 cases](https://openairdocs.org/ntsb-findings/03022032/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Takeoff: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Sonex WAIEX, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=05615ME), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342); cases with it: [Sonex WAIEX, 1 case](https://openairdocs.org/ntsb-events/342/sequence.md?model=05615ME), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Sonex WAIEX, 1 case](https://openairdocs.org/ntsb-events/470/sequence.md?model=05615ME), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis Shortly after takeoff on an instructional flight, the pilots heard a sudden change in engine noise. The instructor scanned the engine instruments and observed that the engine rpm was lower than expected. The instructor took control of the airplane and attempted to return to the airport. The airplane was not able to maintain altitude, and the instructor could not restore engine power to full. Unable to reach the airport, the instructor initiated a forced landing to a field. During the approach, the airplane collided with a power transmission line and impacted terrain. An examination of the engine found that the Nos. 1 and 2 exhaust valves displayed excessive wear. While such wear will result in a loss of engine power, it could not be determined what caused the sudden change in noise and engine power that the pilots experienced on the day of the accident. ## Factual narrative On August 3, 2016, about 1155 central daylight time, a Sonex Limited Waiex airplane, N12YX, impacted terrain following a partial loss of engine power near the Fond du Lac County Airport (FLD), Fond du Lac, Wisconsin. The private rated pilot and flight instructor were both seriously injured. The airplane was substantially damaged. The airplane was registered to and operated by Sonex Ltd under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the light, which operated without a flight plan. The airplane was departing FLD at the time of the accident.According to information provided by the flight instructor, the pilots were performing takeoffs and landing on runway 27 at FLD. Shortly after takeoff, when the airplane was between 200 to 300 ft above ground level, they heard a sudden change in the engine noise. The instructor observed that the engine rpm was between 2,500 to 2,600 rpm, when the engine was previously performing about 3,100 rpm. The instructor took control of the airplane and began an immediate left turn for runway 15. The airplane would not maintain altitude, so he momentarily leaned the mixture which did not improve engine performance, so he returned the mixture to full rich, and performed a forced landing to a field. The airplane collided with an unseen transmission line and impacted terrain. A postaccident examination of the airplane revealed substantial damage to the fuselage and both wings. An examination of the engine was conducted at Sonex under the auspices of the Federal Aviation Administration. A compression check of the engine found low compression of the number 1 and 2 cylinders. Examination of the exhaust valves found they displayed excessive wear. ## Aircraft - Registration: [N12YX](https://openairdocs.org/deregistered/N12YX-2018-01-09), registration cancelled 2018-01-09, S/N 0001, built 2003 (OpenAirDocs) - Reported make and model: SONEX LIMITED WAIEX (NO SERIES) - Registry model: [Sonex WAIEX](https://openairdocs.org/model/sonex-waiex) (registry code 05615ME) (OpenAirDocs) - Registry engine: [Amateur-built UNKNOWN ENG](https://openairdocs.org/engine/amateur-built-unknown-eng) (registry code 99999) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 0001 - Year built: 2003 - Airframe hours: 304.3 - Engines: AMA/EXPR AeroVee 80 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Operator: Sonex Ltd - Registered owner: Sonex Ltd - Airworthiness certificate: Special, Experimental (Special) - Last inspection: 100 hour, February 7, 2016 - Departed: FLD, FOND DU LAC, WI - Destination: OSH, OSHKOSH, WI - Airport: FLD, Fond Du Lac County, runway 27, 3,602 × 75 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 73; injuries: serious; airline transport, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review May 14, 2016; seat: right; restraint: 4-point; flight hours: 29,114 total, 35 in this make and model, 24,019 as pilot in command, 92 in the last 90 days, 9 in the last 30 days - Pilot; age 64; injuries: serious; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 4 knots - Visibility: 10 statute miles - Lowest ceiling: 3,100 ft broken - Temperature: 86 °F, dew point 72 °F - Altimeter: 30.04 inHg - Observed at: KFLD ## 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 20160803013109A](https://openairdocs.org/incident/20160803013109A), Aug 3, 2016: Sonex Limited WAIEX, Fond Du Lac, WI, Substantial damage. On August 3, 2016 at 11:00A.m. a Sonex Waiex, N12YX left oshkosh airport with a flight instructor and student pilot on board for a training flight.… ## Docket (4 files) The files NTSB released with the investigation on December 11, 2017, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=93754. 3.0 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 2.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40458647&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Pilot Statement (item 2, .PDF, 63 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40458648&FileExtension=.PDF&FileName=Pilot%20Statement-Master.PDF - Record of Conversation - FAA Inspector (item 3, .PDF, 101 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40458649&FileExtension=.PDF&FileName=Record%20of%20Conversation%20-%20FAA%20Inspector-Master.PDF - Party to the Investigation (item 4, .PDF, 248 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40458650&FileExtension=.PDF&FileName=Party%20to%20the%20Investigation-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.