Sunday, February 5, 2017

Sonex, N123SX, Sonex Aircraft LLC: Fatal accident occurred June 02, 2015 near Wittman Regional Airport (KOSH), Oshkosh, Winnebago County, Wisconsin

Mike Clark

Jeremy Monnett, sonexaircraft.com 



The National Transportation Safety Board traveled to the scene of this accident.

Aviation Accident Final Report - National Transportation Safety Board:   https://app.ntsb.gov/pdf

Docket And Docket Items - National Transportation Safety Board: https://dms.ntsb.gov/pubdms

Aviation Accident Data Summary - National Transportation Safety Board:  https://app.ntsb.gov/pdf

Sonex Aircraft LLC:   http://registry.faa.gov/N123SX

NTSB Identification: CEN15FA249 
14 CFR Part 91: General Aviation
Accident occurred Tuesday, June 02, 2015 in Oshkosh, WI
Probable Cause Approval Date: 01/11/2017
Aircraft: MONNETT JOHN T JR SONEX SA, registration: N123SX
Injuries: 2 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The pilot and passenger departed on a local flight in the amateur-built experimental airplane using an intersection departure from the runway. Several frames of a surveillance video that captured the airplane during the initial climb from the runway showed a thin white trail of vapor/smoke behind the airplane. GPS data recovered from the airplane indicated that the airplane climbed to about 100 ft above ground level, leveled off, turned left at the end of the runway, and entered a descent. Shortly thereafter, the airplane collided with parked vehicles about 0.25 miles from the departure end of runway. Examination of the accident site indicated that the airplane impacted in a near-vertical attitude, consistent with an aerodynamic stall.

During examination of the wreckage, no evidence of airframe malfunction or failure was detected. The propeller displayed no evidence of rotational damage, consistent with a loss of engine power before impact. The engine's turbocharger would not rotate, and the turbocharger compressor housing displayed impact marks made by the compressor wheel, indicating that there was little relative motion between the blades and the housing at the time of the impact. The turbocharger's wastegate system was tested on an exemplar engine, and no anomalies were noted. It could not be determined whether the turbocharger would not rotate due to impact damage or whether it seized in flight resulting in a partial loss of engine power. Engine test runs with a turbocharger in a seized condition could not be conducted. 

The mixture control lever was found near the idle-cutoff position with a corresponding witness/impact mark around the circumference of the control stem, indicating that the lever was in the cutoff position at the time of impact. It could not be determined at what point during the flight the lever was moved to the cutoff position. Attempts to produce white smoke from the engine by leaning the mixture to the cutoff position and by inducing a loss of engine power due to water contamination were unsuccessful. The exemplar engine's failure to produce white smoke when the mixture was leaned suggests that the loss of engine power was not the result of the pilot moving the mixture control lever to the cutoff position during takeoff. It is possible that the pilot moved the lever to the cutoff position after the airplane departed from controlled flight. The reason for the loss of engine power could not be determined.

The circumstances of the accident are consistent with the pilot failing to maintain sufficient airspeed following a loss of engine power during takeoff, resulting in the airplane's wing exceeding its critical angle-of-attack and a subsequent aerodynamic stall. Instead of using the full runway length of 6,179 ft, the pilot elected an intersection takeoff with about 2,570 ft of available runway. Calculations showed that, had the pilot used the entire runway for takeoff, sufficient runway for a landing following the loss of engine power would likely have been available.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot's failure to maintain sufficient airspeed following a loss of engine power during initial takeoff climb, which resulted in the airplane's wing exceeding its critical angle-of-attack and a subsequent aerodynamic stall. The reason for the loss of engine power could not be determined because examination of the wreckage revealed no mechanical deficiencies. Contributing to the accident was the pilot's decision to conduct an intersection takeoff.



HISTORY OF FLIGHT

On June 2, 2015, about 1520 central daylight time, a Sonex SA amateur-built airplane, N123SX, impacted unoccupied, parked military vehicles at a manufacturing facility shortly after departing the Wittman Regional Airport (OSH), Oshkosh, Wisconsin. The private pilot and pilot rated passenger were fatally injured, and the airplane was substantially damaged. The airplane was registered to and operated by Sonex Aircraft LLC, under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight which operated without a flight plan. The local flight was originating at the time of the accident.

According to OSH air traffic control tower personnel, the airplane departed runway 9 from the intersection of runway 9 and runway 13. After clearing the airplane for takeoff, the tower controller focused his/her attention on inbound traffic and did not witness the accident.

A surveillance video from Oshkosh Defense manufacturing facility captured a portion of the accident flight. The video captured the airplane during its initial climb from the runway. In several of the frames, a wisp of white appears to briefly emanate from the airplane.

PERSONNEL INFORMATION

The pilot, age 40, held a private pilot certificate with ratings for airplane single engine land, airplane single engine sea, and gliders. He was issued a third class medical certificate on February 22, 2013, without any limitations. As of March 15, 2015, the pilot had accrued 715 hours of total time. He was estimated to have at least 540 hours in Sonex type airplanes and 25 hours in the AeroVee Turbo airplane.

AIRCRAFT INFORMATION

The Sonex SA was a low-wing, tailwheel, 2 seat airplane built in 2007, serial number 0008. It was powered by a 100 horsepower AeroVee Turbo engine driving a wood composite, fixed pitch, Sensenich propeller. On June 20, 2007, it was issued a special experimental/amateur-built airworthiness certificate. The original AeroVee engine was removed and the company's prototype AeroVee Turbo was installed on May 8, 2014, which returned the airplane back to Federal Aviation Administration (FAA) Phase 1 test flight period, at a tachometer time of 96.52 hours. Phase 1 was completed on September 23, 2014, at a tachometer time of 118.2 hours. The last recorded maintenance on the airplane was a modification to the cockpit avionics, on January 12, 2015, at a tachometer time of 126.8. Following that maintenance, the airplane was flown cross-country to Florida, and returned back to Oshkosh, Wisconsin, on April 28, 2015. A company mechanic recalled flying with the accident pilot for no more than 1 hour in the days preceding the accident flight and stated the flight was uneventful.

The airplane was last fueled on April 28, 2015, at the De Kalb Taylor Municipal Airport and flown about 125 nautical miles to Oshkosh, Wisconsin.

METEOROLOGICAL INFORMATION

At 1537, an automated weather reporting facility located at the Wittman Regional Airport, reported wind from 130° at 11 knots, visibility 10 miles, a clear sky, temperature 72° F, dew point 39° F, and an altimeter setting of 30.10 inches.

AIRPORT INFORMATION

The Wittman Regional Airport is a public airport with a control tower, and it is serviced by 4 runways aligned with 18/36, 9/27, 5/23, and 13/31. The airplane departed from runway 9, which is a 6,179 foot long, grooved concrete reported to be in good condition. The pilot elected to do an intersection takeoff from the intersection of runway 9 and 13, with about 2,570 feet of available runway for the takeoff.

WRECKAGE AND IMPACT INFORMATION

The accident site was located about a ¼ mile east-northeast of the departure end of runway 9. The airplane came to rest on a general heading of 220 degrees on unoccupied parked military vehicles located on Oshkosh Defense property. All components of the airplane were found in the immediate vicinity of the accident site. The engine separated from the airplane and was located on the ground in front of the airplane. All major components remained attached to the airplane. The airplane was transported to a secure facility for further examination.

Both wings displayed impact damage. The leading edge of the left wing was twisted rearward. The left flap remained attached to the left wing. The left aileron remained attached to the aileron push/pull rod. The outboard portion of the left aileron as well as the outboard portion of the left wing outboard of the aileron control rod section was torn and separated. The leading edge of the right wing displayed rearward accordion crushing. The right aileron and flap remained attached to the wing. The empennage was distorted and wrinkled near the aft cockpit and relatively undamaged near the rudder. The horizontal stabilizers, vertical stabilizer, and rudder were not damaged. Both elevators were buckled at their inboard sides. Flight control continuity was established from the ailerons to a section under the cockpit control stick. In addition, elevator continuity was established from the elevators to the same section under the cockpit control stick. This area was crushed and distorted resulting in an inability to smoothly move the cockpit controls. Continuity to the rudder was established to the rudder pedals. The flaps appeared to be in the retracted position. The flap selector bracket was deformed and flap handle was bent away from the bracket. Both throttles (left and right seat positions) were in the full forward position. The mixture control was near the idle-cutoff position with a corresponding witness/impact mark around the circumference of the control stem. The elevator trim was near the full nose down position, which, according to the company, was an area normal for takeoff in this airplane. No preimpact anomalies were detected with the airframe.

The propeller remained attached to the engine. Both tips of the wooden propeller were fractured in an aft direction. There were gouges on the nose cone of the propeller. No rotation scoring was detected on the propeller nose cone or the propeller blades.

The AeroInjector carburetor was impact separated from the engine, but remained connected to the airframe via the throttle and mixture cables. The intake housing to the turbocharger was impact separated. The cylinder rocker box over the No. 3 and 4 cylinders was also impact separated. There was some rearward distortion to the No. 3 and 4 valve rocker arms and rod housings. Engine continuity was confirmed through the engine to the flywheel. In addition, valve train continuity was established. Seven of the 8 spark plugs were removed and examined. None of the spark plugs appeared excessively gapped and were not fouled. The top No. 1 spark plug was bound tightly, so it was not removed during the examination to prevent any damage to the plug or housing. Oil was detected throughout the engine. All four cylinders were borescoped and found to have normal wear and deposits on the cylinder bores, pistons, and valves. The AeroInjector's throttle slide operated smoothly and normally, and its needle valve was installed in the proper orientation. The needle valve was unobstructed and channeled fuel when fuel was added to the AeroInjector's fuel inlet.

The engine's turbocharger could not be rotated by hand. Disassembly of the turbo found static marks corresponding to compressor blades without any smearing or deformation of the blades. Disassembly of the turbo found that the bearing housing was cracked. Disassembly was halted after finding a crack in the housing and the component was shipped to the NTSB materials laboratory in Washington D.C. for further examination.

The airplane was equipped with a MGL Avionics iEFIS Lite electronic flight instrument system. The unit's micro SD card and portions of the iEFIS were shipped to the NTSB vehicle recorders laboratory for data download.

MEDICAL AND PATHOLOGICAL INFORMATION

An autopsy was performed on the pilot by the Fond du Lac County Medical Examiner as authorized by the Winnebago County Coroner's Office. The cause of death was multiple traumatic injuries.

The FAA Civil Aerospace Medical Institute performed forensic toxicology on specimens from the pilot. Testing was negative for carbon monoxide and ethanol. Ibuprofen was detected in cavity blood. Ibuprofen is a non-narcotic analgesic and anti-inflammatory agent.

TESTS AND RESEARCH

Turbocharger

The turbocharger was sent to the NTSB materials laboratory for examination. Sonex did not provide turbocharger manufacturer information regarding the components of the turbocharger assembly, but did provide an exemplar assembly for comparison with the accident assembly. No manufacturer identification marks were present of the exemplar turbine or compressor housings. The manufacturer name and serial number for the exemplar wastegate actuator were present on the left face of the exemplar wastegate actuator housing. However, the left face of the accident wastegate actuator housing had an unpainted machined surface, and both the manufacturer and serial number were missing.

Impact marks were located at the upper and aft portions of the compressor housing surface. The impact marks were relatively distinct and discrete consistent with little relative motion between the blades and the housing at the time of impact. Corresponding blade damage was observed on the compressor wheel. Six of the compressor blades had radial cracks that emanated inward from the outer edges. The cracks were all associated with deformation of the blade where the airfoils between the cracks and the blade tip were bent toward the pressure face of the blade (toward the direction of rotation). Both the compressor wheel and turbine wheel turned together freely within the center housing when either wheel was rotated by hand. The flange for attaching the center housing to the compressor housing was fractured around the circumference. The fracture surface was uniform and rough consistent with overstress fracture. The location of the fracture was consistent with the compressor housing moving to the right relative to the center housing.

While differences were noted between the accident and exemplar wastegate actuator in terms of spring coil diameter and number of coils, the displacement response was very close between the two actuators.

The accident wastegate actuator was shipped to Sonex for further testing on a test cell engine.

Wastegate Actuator Functional Testing

The accident engine was impact damaged and could not be used to conduct testing. The accident wastegate actuator was installed on a test bed engine. Under the auspices of the NTSB and FAA, the engine was started and run to maximum power. The wastegate opened when manifold pressure exceeded 43 inches and maintained manifold pressure between 40 to 43 inches. Engine RPMs varied but were generally about 3,100. The wastegate actuator was then opened and the engine functionally tested. The engine produced about 2,500 RPM and manifold pressure was between 28 to 29 inches.

The actuator was returned to normal operation and the engine functionally tested. Attempts to replicate a production of white smoke from the engine were attempted utilizing the full range of mixture level motion and speeds and included forcing a loss of engine power due to water intrusion. The attempts to replicate the production of white smoke using the test engine were unsuccessful.

Of note, actual engine performance with a turbocharger in a seized condition could not be conducted. A company employee reported he experienced a degraded turbocharger system a few weeks prior to the engine functional test. During that flight, the airplane would fly level, but could not maintain a positive climb. He reported that after the flight, the turbo was examined and found to not be completely seized, but the piston ring-type seal on the shaft connecting the compressor and turbine wheels had partially seized and interfered with the shaft's ability to rotate. An examination of the accident turbocharger did not find a similar signature. Replicating a seized turbocharger during engine operation was not possible.

Engine Disassembly

The accident engine was disassembled and no preimpact anomalies were detected with the engine.

MGL Avionics iEFIS Lite and micro SD card

The micro SD card did not contain any flight performance data for the accident flight, or any flights prior to the accident. Only GPS coordinate and altitude information could be retrieved directly from the iEFIS. However, this data did not include time information, so airplane performance could not be evaluated.

Of the data available, the recording began near the intersection of runways 9 and 13. The airplane departed near taxiway alpha and climbed to about 100 feet above ground level. It then leveled off and turned left over railroad tracks at the end of the runway and began a descent, at which point the recording ended.

ADDITIONAL INFORMATION

Runway Available

The accident airplane's ground run was about 1,700 feet before the airplane took off from the runway. The airplane climbed straight ahead for about 2,150 feet before beginning a left turn. The distance traveled during the left turn to the accident site was approximately 583 feet. A departure from runway 9 and taxiway B1 would have provided about 5,695 feet of runway available.


NTSB Identification: CEN15FA249
14 CFR Part 91: General Aviation
Accident occurred Tuesday, June 02, 2015 in Oshkosh, WI
Aircraft: MONNETT JOHN T JR SONEX SA, registration: N123SX
Injuries: 2 Fatal.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

On June 2, 2015, about 1520 central daylight time, a Monnett Sonex SA experimental amateur-built airplane, N123SX, impacted unoccupied vehicles, after departing the Wittman Regional Airport (OSH), Oshkosh, Wisconsin. Both private pilots were fatally injured. The airplane was substantially damaged. The airplane was registered to and operated by Sonex Aircraft LLC, under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight which operated without a flight plan. The local flight was originating at the time of the accident.

According to OSH tower personnel, the airplane departed runway 9 from the intersection of runway 9 and runway 13. After clearing the airplane for takeoff, the tower controller focused their attention on inbound traffic and did not witness the accident.

The accident site was located 0.25 miles east-northeast of the departure end of runway 9. The airplane came to rest on unoccupied vehicles located on Oshkosh Corporation's property on a general heading of 220 degrees. The engine separated from the airplane and was located on the ground in front of the airplane. All major components remained attached to the airplane. The airplane was transported to a secure facility for further examination.

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