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On May 5, 2002, at 1440 eastern daylight time, a Yoder GP-4, N59JY, piloted by a private pilot, was destroyed on impact with terrain about 10 nautical miles east of Mount Pleasant, Michigan. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 flight was not operating on a flight plan. Both private pilots were fatally injured. The local flight originated from Jack Barstow Airport, Midland, Michigan.
A witness located about 2,600 feet east of the accident site stated that he was in his yard when heard the engine sputter but could not see the airplane. While looking towards the west, he saw the airplane at the top of some pine trees spinning in a level attitude. The airplane then impacted the ground in a level attitude with no smoke and no fire. There was no smell of fuel.
The pilot seated in the right seat, age 65, held a private pilot certificate with airplane single engine land and instrument airplane ratings. On January 18, 2001, he applied for a third class medical certificate which was deferred for further evaluation due to a history of Parkinson’s disease. At the time of his application, he reported a total flight time of 1,925 hours, of which 5 hours were over the past 6 months. He was then issued a special issuance of a third class medical certificate with an expiration date of January 31, 2003.
The pilot seated in the left seat, age 62, held a private pilot certificate with an airplane single engine land rating. He was issued a third class medical certificate on February 25, 1975, at which time a total flight time of 300 hours was reported. There were no additional issuances of a medical certificate after this date.
The 1996 GP-4, serial number 158, was built by the right seat pilot and was registered on May 31, 1996, as an amateur built experimental airplane. The airplane had a 2-seat side-by-side seating arrangement.
According to the manufacturer, the unmodified GP-4 stalling speed in the landing configuration (Vso) is 54 knots indicated air speed (KIAS). The stalling speed (Vs) is 64 KIAS.
WRECKAGE AND IMPACT INFORMATION
The airplane was lying in a ditch along a road and near a residence. Ground scarring was limited to an area beneath the airplane's platform. The bottom of the fuselage exhibited crushing in the vertical direction. One of the propeller blades was oriented vertically in the ground. The empennage was bent laterally towards the left as viewed from tail to nose.
The left and right fuel tanks were broken open and were noted not to contain baffles. The fuel selector was selected to right fuel tank. Inspection of the fuel selector did not reveal any obstructions. No residual fuel was found in the fuel tanks, flow divider, injector lines, or the fuel lines leading and exiting the fuel pump. About one week after the accident, vegetation near the broken areas of the fuel tanks were blighted. The electric fuel pump was removed from the engine and connected to an electrical source. The fuel pump then rotated and produced thumb pressure. The cockpit electrical fuel pump switch was in the off position.
Inspection of the engine revealed that it was equipped with one magneto and an aftermarket electronic ignition in the place of the second magneto. The top spark plugs were removed and exhibited no anomalies. Engine continuity to the accessory section was confirmed when the engine was rotated by hand. The expulsion and suction of air was also noted through the top spark plug holes.
Examination of the flight control system confirmed continuity from the control surfaces to their respective cockpit flight controls.
MEDICAL AND PATHOLOGICAL INFORMATION
Autopsies of both pilots were performed by the Midland County Medical Examiners Office on May 5, 2002.
Federal Aviation Administration (FAA) toxicological testing of the right seat pilot detected L-Methamphetamine in blood. L-Methaphetamine is found in nasal inhalers and is also a metabolite of selegiline.
FAA toxicological testing of the left seat pilot was negative for all substances tested.
TEST AND RESEARCH
GP-4 engine drawing plans are based upon a Lycoming IO 360-A1A engine The accident airplane was modified with a Lycoming O-540 series engine. The plans also indicate that the wing fuel tanks are to have baffles spaced at 124 inch intervals fuel vents located at each wing tip.
The GP-4 designer-builder said that the GP-4 drag area was built around the Lycoming IO-360 engine. The pilot contacted him regarding modification that he was making to the accident airplane. He said that the accident airplane had a Lycoming 540 engine, which was about 200 lbs greater than the IO-360. He added that for the pilot to get the airplane balanced, he would have had to made other modifications. The fuel system was changed in order for the airplane to be equipped with a wet leading edge. The designer said that he never flew the accident airplane but it was highly modified and he tried to talk the pilot out of making these modifications. When asked if he had performed spin testing on the GP-4, he replied by saying that the GP-4 was spun from accelerated and departure stalls to the right and left. In each instance, it took 1 3/4 rotations to recover. He also added that the GP-4 is very responsive and that he has never seen a situation where the GP-4 would be dangerous.
A pilot who had flown a GP-4 for 15 hours with another pilot stated that during a flight, he slowed the airplane while the other pilot lowered the landing gear. He then established an airspeed of 80 mph. a little nose high with power in almost idle and told the other pilot to raise the landing gear. He let the aircraft enter an initial buffet at an airspeed of 68-70 mph. While the other pilot was raising the landing gear, he intentionally applied some back pressure on the stick, and the airplane immediately pitched down and snapped to the left. He told the other pilot that if this was to occur to someone who was not fully expecting it, then he believed that the airplane would snap into an inverted spin before they could initiate recovery procedures.
A second pilot who had flown a GP-4 stated that during a flight, he retarded throttle to idle, slowed the airplane to an indicated airspeed of 80 mph and the altered the pitch attitude to decelerate at a rate of about 1 mph per second until initial stall buffet occurred, which was about 65 mph with a full stall occurring shortly thereafter about 61-62 mph. He stated that power off recovery was easily accomplished. During this power off, gear down, flaps up configuration, initial buffet was easily identified; however, when the airplane stalled it rapidly pitched down and banked sharply to the left. At no time did he allow or did the airplane exceed 60 degrees of bank angle, or more than 30 degrees nose-down pitch attitude.
According to Flying Qualities and Flight Testing of the Airplane, Chapter 12, Figure 12.5a, Tail configurations which are good, bad and likely to be dangerous..., there are 6 tail configuration with descriptions of their spin qualities related to tail configurations. Tail configuration (6), which is consistent with the GP-4, is described as, "Tails which make a test pilot stop and suck his teeth." The figure also contains the statement, "As a rough rule have at least 1/3 of the rudder area outside the wake of the stabilizer, approximated as shown." The wake is defined by a 60 degree line at the leading edge and a 30 degree line at the trailing edge horizontal stabilizer. Both lines are drawn from the stabilizer's chord line.
There are no FAA spin requirements for airplanes certified as experimental category airplanes. Small airplanes certified under FAR 23 are required to meet certain spin requirements. Advisory Circular (AC) 23-8, Flight Test Guide For Certification of Part 23 Airplanes provides information and guidance concerning acceptable means, but not the only means of showing compliance with Part 23. In all cases, the effects of gear, flaps, power, accelerated entry, and normal and abnormal control use should be investigated. A suggested matrix in AC-23-8 lists 13 flight conditions for tests in which normal and abnormal spin controls during a left and right spins are performed.