NTSB Factual Report

HISTORY OF FLIGHT

On November 6, 2009, at 1005 central standard time, a Zenith Aircraft Company Zodiac 601 XL, experimental light sport airplane, N538CJ, was destroyed when it impacted terrain, following an in-flight breakup near Agnos, Arkansas. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of 14 Code of Federal Regulations Part 91 without a flight plan. The sport pilot was fatally injured. The cross country flight departed Sharp County Regional Airport (KCVK), Ash Flat, Arkansas, at 0848.

The property owner discovered the wreckage of the accident airplane in his field. There were no known or identified witnesses to the events that led up to the accident flight or impact sequence. Federal Aviation Administration (FAA) radar data was not available for the accident flight. The pilot was not in communications with other pilots or airport ground personnel in the area or air traffic control at the time of the accident.

The debris field was scattered over 600 feet on a magnetic bearing of 35 degrees initiating with the right wing assembly which came to rest in a pond. The left wing assembly came to rest forward of the right wing. The left wing spar, left wing fuel tank, various cockpit items, and personal effects were located in the debris field. The fuselage, empennage, engine, and propeller assembly came to rest, inverted, approximately 600 feet from the right wing. There were no ground scars identified between the right wing and the main wreckage that could be associated with the left or right wing, empennage, or fuselage.

The wreckage was recovered and relocated to a facility in Clinton, Arkansas, for further examination.

PERSONNEL INFORMATION

The pilot, age 71, held a sport pilot certificate issued on January 12, 2008. In addition, he held a repairman certificate for light sport aircraft – Zodiac 601 XL, N538CJ. He was issued a third class airman medical certificate/student pilot certificate on July 24, 2007. The medical certificate contained the limitations “holder must wear corrective lenses” and “not valid for any class after May 31, 2008.” The pilot held a valid driver’s license for the state of Illinois.

The pilot’s personal flight logbook was located in the vicinity of the main wreckage. The cover and first four pages of the logbook had torn and were not found within the main wreckage or debris field. A review of the logbook indicated that the pilot had logged 116 hours of flight time, of which 77 hours were in the accident airplane make and model. The pilot had logged two hours in the previous 90 days. According to the logbook, the pilot successfully demonstrated the skills required to be proficient for a sport pilot certificate on January 12, 2008.

AIRCRAFT INFORMATION

According to FAA records, the pilot/owner manufactured the 2007 experimental light sport airplane, a Zenith Zodiac 601 XL (serial number 6-6528). It was registered with an FAA special airworthiness certificate in the category of experimental for light sport operations. Block 8A “Existing Aircraft without an airworthiness certificate & do not meet 103.1” was checked. A Jabiru 3300 engine rated at 120 horsepower at 3,300 rpm powered the airplane. The engine was equipped with a two-blade Sensenich propeller.

The airplane registered to and operated by the pilot was maintained under an annual condition inspection program. The maintenance records were not with the airplane wreckage. Several requests were sent to the owner’s estate, requesting that the maintenance records and airplane information, or copies of those records and information be provided to the National Transportation Safety Board (NTSB) for their review. These records were not located by the bank handling the estate. Requests sent to family members were not responded to.

FAA records showed that Zenith Aircraft Company manufactured the accident airplane. However, the bill of sale for the airplane showed that it was a kit that had been sold from Zenith Aircraft Company, Mexico, Missouri, and the aircraft manufacturer was listed as “Charles Cummings,” with the Zodiac 601 XL designated as a kit.

Following the accident, a representative from Zenair in Canada (also a party to the accident investigation) informed the NTSB investigator-in-charge (IIC) that the accident pilot had previously experienced and reported an encounter with flutter in the accident airplane. The NTSB made contact with the owner of Flight Crafters who was identified as the source of this report. This individual clarified that the pilot had not reported this encounter to him, but rather he had heard of this encounter through other pilots in the area. Multiple attempts were made to locate the individual with whom the pilot had spoken with regarding the flutter event. This report could not be substantiated through first hand information, fact gathering, or interviews.

A review of the Experimental Aircraft Association (EAA) safety program records revealed that the owner/builder had not participated in either the EAA Flight Adviser or the EAA Technical Counselor Programs.

METEOROLOGICAL CONDITIONS

The accident site was located between several official weather observation stations. The closest official weather observation station was Batesville Regional Airport (KBVX), Batesville, Arkansas, located 35 nautical miles (nm) south of the accident site. The elevation of the weather observation station was 465 feet mean sea level (msl).

The routine aviation weather report (METAR) for KBVX, issued at 1015, reported winds 170 degrees at 10 knots, gusting to 15 knots, visibility 10 statute miles, sky condition few clouds at 3,400 feet, temperature 17 degrees Celsius (C), dew point 04 degrees C, altimeter 30.25 inches of Mercury.

The METAR report for Walnut Ridge Regional Airport (KARG), Walnut Ridge, Arkansas, issued at 0955, (located 38 nm east-southeast of the accident site) reported winds 180 degrees at 8 knots, visibility 10 statute miles, sky condition clear, altimeter 30.27 inches of Mercury. Temperature and dew point were not reported.

The METAR report for Ozark Regional Airport (KBPK), Mountain Home, Arkansas, issued at 0953 (located 38 nm west of the accident site) reported winds 180 degrees at 8 knots, visibility 9 statute miles, sky condition clear, temperature 18 degrees C, dew point 10 degrees C, altimeter 30.19 inches of Mercury.

Two regional pilot reports (PIREPS) issued at 1153 and 1444 reported no turbulence. An Airmen’s Meteorological Information (AIRMET) for moderate turbulence below 8,000 feet was in effect for the accident airplane’s route of flight. There were no Significant Meteorological Information (SIGMETS) active for the area at the time of the accident.

In addition to the official weather observation stations, a Department of Interior weather station, designation ESDA4, was located 12 nm south-southwest of the accident site at an elevation of 538 feet. The station reported winds at 179 degrees at 4.33 knots with wind gusts to 10.44 knots.

FLIGHT RECORDERS

A Garmin GPSMap 296 handheld global positioning system (GPS) unit was located within the wreckage of the accident airplane. The unit was recovered and sent to the NTSB Vehicle Recorders Laboratory in Washington, D.C., for download. Upon arrival at the lab, power was applied to the unit and the recorded waypoint, route, and track log data were successfully downloaded from the unit via the USB port.

Eighty-six user defined waypoints, one user defined route, and 118 track logs were downloaded from the unit. This data included date, time, altitude, distance from previous update, time since previous update, average groundspeed since previous update, average course since previous update, and the latitude and longitude at the time of the update.

The track log data from the date of the accident started at 0848:06 and ended at 1004:56. The last position of the airplane was recorded at 36 degrees 15.061 minutes north latitude and 91 degrees 41.449 minutes west longitude. The last calculated groundspeed velocity of the airplane was 117 miles per hour. The last calculated course of the airplane was 081 degrees true.

The plotted data depicted the accident airplane depart KCVK and fly southwest towards Horseshoe Bend Airport (K6M2), Horseshoe Bend, Arkansas. The data was consistent with the performance of a touch and go landing at K6M2, and then a northeasterly departure from K6M2.

WRECKAGE AND IMPACT INFORMATION

The wreckage was located in a sparsely vegetated hilly field just south of Agnos, Arkansas. The right wing initiated the debris field, coming to rest inverted in a pond at a measured elevation of 820 feet. The wing included the right aileron and right flap; both remained attached to the wing assembly.

The left lower wing spar cap was located approximately 55 feet from the right wing. This spar separated from the left wing, and was bowed, forming a semi-circular shape.

The left wing was located approximately 190 feet from the right wing at a measured elevation of 838 feet. The left wing came to rest inverted. The left wing included the left aileron and left flap; both remained attached to the wing assembly. The leading edge of the left wing separated partially from the wing assembly along the lower rivet line from the wing root outboard to the landing light.

The left fuel tank came to rest 96 feet from the left wing. The fuel tank was bent and broken due to impact damage. Adjacent to the left fuel tank was a semi-circular ground scar, consistent in shape with the fuel tank. The ground scar contained a fluid consistent in color, smell, and texture with aviation fuel.

The main wreckage was located 295 feet from the fuel tank and came to rest inverted, directly beneath power lines and adjacent to a tree. The main wreckage consisted of the fuselage, empennage, and engine and propeller assembly. The empennage consisted of the horizontal and vertical stabilizer, rudder, and elevator. The empennage remained attached to the fuselage. The vertical stabilizer was crushed to the left, nearly 90 degrees.

The fuselage included the cabin area, instrument panel, and the flight controls, including the control cables for the right and left ailerons, rudder, and elevator. The main landing gear assembly separated from the main wreckage and came to rest adjacent to the main wreckage. The engine assembly remained attached to the fuselage. The engine was embedded in the ground approximately one foot.

The elevator control cables were continuous from the forward fuselage, through the autopilot servo to the elevator. The rudder cables were continuous from the forward fuselage aft to the rudder. The aileron cables were continuous from the cabin area outboard to the left and right bell cranks. Both aileron bell crank assemblies separated from the left and right wings.

MEDICAL AND PATHOLOGICAL INFORMATION

The Arkansas State Crime Laboratory performed the pilot’s autopsy on November 9, 2009. The autopsy concluded that the cause of death was due to “blunt force injuries.”

The FAA’s Civil Aerospace Medical Institute, Oklahoma City, Oklahoma, performed toxicological tests on specimens that were collected during the autopsy (CAMI Reference Number 200900281001). Results were negative for carbon monoxide, cyanide, and ethanol. Atenolol and valsartan were detected in the urine and blood, and ibuprofen was detected in the urine.

TESTS AND RESEARCH

Aileron/Wing Design

The ailerons were protected from flutter through the use of high aileron control cable tension. The high cable tension altered the dynamic interaction between the wing and aileron, similar to increasing the stiffness of the wing. High cable tensions provided a level of protection from aileron flutter. After several accidents in Europe, the United Kingdom Light Aircraft Association designed and flight tested ailerons fitted with counter balances. Counter balances are considered a more direct mitigation strategy to prevent aileron flutter.

Wreckage Examination

The wreckage examination was conducted by investigators from the NTSB, including two aeronautical engineers, and was attended by representatives from FAA and Zenair on November 8, 2009. An additional wreckage examination was conducted on June 15, 2010, by NTSB investigators.

Right Wing

The leading edge of the right wing, inboard of the wing locker was crushed in. The upper skin on the right wing, between spars, exhibited 45-degree skin wrinkles emanating from the inboard edge of the aileron. A circular witness mark, black in color, was documented on the lower wing skin consistent with contact with the right main landing gear tire.

The center section of the wing spar remained attached, through to the fuselage support bracket on the opposite side of the fuselage. The lower spar cap exhibited a twist consistent with the wing trailing edge moving up. The upper cap also exhibited a twist, with some forward bending, also consistent with the wing trailing edge moving up.

Multiple witness marks were noted on the upper, leading edge surface of the right flap, corresponding with the adjacent rivet line along the trailing edge of the right wing. A flap stop had been installed on the trailing edge of the wing. The three rivets utilized to secure the stop had not been painted consistent with recent or new installation.

The right aileron remained attached to the wing and exhibited one impact mark adjacent to the aileron stop. When examined, the existing damage prevented deflecting the aileron to the point required to contact the aileron stop. The right aileron bell crank was attached to the support structure (a wing rib) and to the cable. The assembly and small portion of the wing rib were separated from the wing structure and also from the aileron. Tension in the cable assembly prior to the breakup could not be quantified.

Left Wing

The leading edge skin on the left wing was detached from the lower surface of the wing. The skin remained attached to the upper surface of the wing along the main spar. A long, narrow black mark was noted on the bottom of the wing skin consistent, in texture and color, with contact with the left main landing gear tire. The upper wing skin, between the first four spars lines, exhibited diagonal wrinkles.

The lower spar cap for the left wing separated from the wing assembly. The upper spar cap was bent down. The left wing fuel tank separated from the wing assembly.

Multiple witness marks were noted on the upper, leading edge surface of the left flap, corresponding with the adjacent rivet line along the trailing edge of the left wing. A flap stop had been installed on the trailing edge of the wing. This flap stop was thicker than the flap stop installed on the right wing. The three rivets utilized to secure the stop had not been painted consistent with recent or new installation. The outboard edge of the left flap was bent.

The left aileron remained attached to the wing. The outboard hinge was broken. The left aileron bell crank was attached the support structure (a wing rib) and to the cables. The assembly and small portion of the wing rib were separated from the wing structure and also from the aileron. The aileron trim tab exhibited a stream wise tear on the upper surface. Tension in the cable assembly prior to the breakup could not be quantified.

Flap Control Assembly

The right and left flap extension was driven by a small motor, mounted directly aft of the pilots seat. Examination revealed a loose condition in the flap control arm. Further examination revealed that the loose condition existed between the motor control arm and the left flap control arm. Two bolts, measuring 1 and ¾ inches in length, were utilized to attach the left control arm to the through bar, and motor control arm. The bolts were secured through corresponding holes with the motor and right and left control arm assemblies, utilizing a lock nut and one single washer between the nut and arm. Disassembly of flap control assembly revealed multiple witness marks between the control arm surface and the bolt. The lock nut was as far down on the bolt as the threads woul

NTSB Probable Cause

The in-flight separation of both wings due to aileron flutter. The aileron flutter was the result of inadequate wing stiffness and the lack of aileron counterbalances.