On July 23, 2001, at 1115 central daylight time, a Schnitz FIIC-2 Goshawk experimental, amateur-built, tandem-seat airplane, N393Y, was destroyed when it impacted a tree and terrain in an uncontrolled descent at the Zuehl Airport near Marion, Texas. The commercial pilot in the front seat was fatally injured, and the airline transport pilot in the rear seat sustained serious injuries. The airplane was registered to and operated by the front seat pilot. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 test flight. The local flight was initiating at the time of the accident.

During a telephone interview conducted by the NTSB investigator-in-charge, a witness stated that it was the first flight for the bi-wing airplane. The witness stated that the airplane was observed making a few high-speed taxis. The airplane eventually took off and made a "sharp turn to the left." The airplane then "stalled," impacted terrain in a nose low attitude and caught fire.

The FAA inspectors, who responded to the accident site, reported that witnesses, located at the airport, observed the airplane taxi "down runway 17 at a high speed and get airborne with the aircraft in a crab condition. The engine speed momentarily decreased and the aircraft lost altitude and regained speed and came back to the runway regaining directional control" before coming to stop at the end of the runway. The witnesses reported that the airplane was taxied back to its hangar, and after 10-15 minutes, the airplane returned to runway 17. The witnesses heard the engine RPM increase and observed the airplane roll down the runway. The airplane lifted off and the engine speed decreased and increased momentarily "as if it surged." The airplane then banked to the left, approximately 300 feet above the ground, and the engine speed "surged again." The airplane was then observed losing altitude until it impacted a tree.

According to the FAA inspectors, the airplane impacted a tree and terrain east of the runway. The inspectors reported that the tree was freshly cut approximately 4 feet above the ground. The airplane's fuselage was compresssed between the engine and the front cockpit. The aft portion of the engine and the front cockpit sustained fire damage.

FAA inspectors conducted an interview with the rear seat pilot on September 8, 2001. During the interview, the rear seat pilot stated that it was his understanding that the airplane was not supposed to takeoff. The intention of the owner's operation was to conduct some taxi runs. The rear seat pilot reported to the FAA that it was the first taxi attempt, and he thought that the front seat pilot took off near the end of the runway. He also told the FAA inspectors that he informed the front seat pilot prior to the flight that he didn't want to fly the aircraft as he felt it was unsafe. He reported that the "ailerons did not have full travel and that the strakes were hitting the flying wires."

The front seat pilot was issued a third class medical certificate on April 7, 2000, with the limitation that he wear corrective lenses. He held a commercial pilot certificate with airplane single and multi-engine land and sea ratings, and an instrument airplane rating. According to his last medical certificate application, he had accumulated 5,250 total flight hours, of which 4 hours were accumulated within the preceding 6 months.

The rear seat pilot was issued a first class medical certificate on April 16, 1999. He held an airline transport pilot certificate for multi-engine land airplanes, and a private pilot certificate for single-engine land airplanes. According to the rear seat pilot's last medical application, he had accumulated a total of 9,000 flight hours.

An autopsy was conducted on the front seat pilot at the Travis County Medical Examiner's Office. According to the medical examiner, the pilot died as a result of "multiple traumatic injuries." Toxicology tests for carbon monoxide, cyanide, ethanol, and drugs were conducted on the front seat pilot. The toxicology results revealed that 0.05 ug/ml of diphenhydramine was detected in the pilot's blood, an unquantified amount of diphenhydramine was detected in the liver, and 1.076 ug/ml of acetaminophen was detected in the pilot's blood. Acetaminophen is an over-the-counter pain reliever commonly known by the trade name Tylenol. Diphenhydramine is an over-the-counter antihistamine used in symptomatic management of allergic symptoms and also for its sedative, antitussive and antispasmodic effects (commonly known by the trade name Benadryl). The American College of Physicians-American Society of Internal Medicine conducted a study (Effects of Fexofenadine, Diphenhydramine, and Alcohol on Driving Performance) on the effects of diphenhydramine on driving performance. The results of that study indicated that "Participants had significantly better coherence after taking alcohol or fexofenadine (Allegra) than after taking diphenhydramine...After participants took diphenhydramine, driving performance was poorest, indicating that diphenhydramine had a greater impact on driving than alcohol did."

The airplane was an 85% scale replica of a Navy F-IIC-2 Goshawk, constructed from plans and certificated as an experimental amateur-built airplane on May 17, 2001, when it was approved for phase 1 operations (first 40 hours of flight). The FAA inspector, who issued the experimental airworthiness certificate, reported that he checked the flight controls prior to issuing the certificate. The tandem-seat airplane was equipped with dual flight controls for the front and rear seats; however, the front seat only had a throttle control, whereas the rear seat cockpit area had a throttle, mixture, and propeller control, the magneto and ignition switches, and the majority of engine and flight instruments. The airplane was equipped with a Lycoming R-680-13 radial engine and a Hamilton Standard 2-bladed constant speed propeller. The aircraft's construction and maintenance records were not recovered during the course of the investigation.

According to personnel at the airport, the front seat pilot had been working on the airplane for over a year and had never flown it. They also reported that the pilot had the propeller governor removed and reinstalled a few days prior to the accident.

The NTSB investigator-in-charge (IIC) examined the Hamilton Standard 1M12-G propeller governor on February 14, 2002. The governor base was partially separated and the drive gear coupler was separated from the governor. The remainder of the base was removed from the governor and the booster pump drive gear/shaft was rotated. The drive gear shaft would not rotate freely and would stick as if meeting a detent. The remaining governor sections were removed and examined. No other anomalies were noted with the governor components. According to the Hamilton Standard propeller governor service manual, the pilot valve is supposed to slide within the booster pump drive gear/shaft freely and should "fit in the drive gear shaft in any angular position without binding." When the NTSB IIC removed the pilot valve from the drive shaft, the pilot valve would stick and took a considerable amount of force to remove. The internal part of the shaft was coated with what appeared to be a cooked oil coating. It could not be determined if the cooked oil coating was a result of the post crash fire or a pre-existing condition.

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