NTSB Factual Report

HISTORY OF FLIGHT

On October 23, 1998, approximately 1552 central daylight time, a Kolb Twinstar TA-2 two place ultralight, N4281Z, owned and operated by the pilot, was destroyed during impact with terrain while on the downwind leg at the Coulter Field Airport, near Bryan, Texas. The non-instrument rated private pilot, sole occupant of the ultralight, was fatally injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the personal flight conducted under 14 CFR Part 91. The local flight originated from the Coulter Field Airport about 3 minutes prior to the accident.

Witnesses at the airport reported to local law enforcement personnel that they talked to the pilot earlier in the day, and the pilot had told them that he was going to take the "machine for a flight because he had a prospective buyer coming to look at it." The same witness stated that he was under the impression that the pilot had ordered a kit plane to replace his current ultralight.

A witness at the airport observed the ultralight takeoff to the south from the taxiway (old runway 17). According to the witness, the ultralight "climbed to somewhere between 300 and 500 feet above the ground." The engine sounded "like it was producing good power." He further observed the ultralight complete a 90 degree turn to the east [crosswind], followed by another left 90 degree turn [downwind], prior to observing "the airplane nosed vertically into the ground." The entire sequence of the flight took about 3 minutes." Witnesses explained that it is common practice for ultralights and gliders to operate from that taxiway in order to stay out of the way of conventional traffic at the airport.

Another witness reported that she observed what appeared to be a shinny piece of metal trailing behind the ultralight. The witness further reported that it appeared to her that the ultralight was returning to the airport. The witness stated that "the nose of the ultralight bobbed up and down a couple of times" followed by the "airplane nosing over to the near vertical position." The witness stated that she lost sight of the ultralight as it descended behind trees north of the airport.

PERSONNEL INFORMATION

The 74-year-old pilot received his private pilot certificate on February 19, 1986. He held a current FAA third class medical certificate, issued on June 4, 1997, which was valid for "student pilot purposes only." The pilot was reported to have accumulated a total of 1,205 flight hours, of which 2 hours were in the accident ultralight.

A friend of the pilot reported to the NTSB investigator in charge, that the pilot previously owned a Cessna 172, which he operated while he worked as a professor at the local university. The pilot was wearing a helmet at the time of the accident.

AIRCRAFT INFORMATION

The tailwheel equipped, 30 foot wingspan, 2 place (side by side), dual control ultralight featured a 3-axis conventional flight control system. The 1991 model ultralight was powered by a two cycle, 2 cylinder, 497 cubic centimeter Rotax engine capable of developing 47 horsepower. The engine, which was installed in the pusher configuration, was driving a wooden propeller. The ultralight was not equipped with 2-way radio communication.

According to the kit manufacturer, the Twinstar is not equipped with an elevator trim tab. Trim in the standard Twinstar is accomplished by adjusting the spring tension on the elevator control cable from inside the fuselage cage near the control stick. The accident ultralight had been modified by the addition of a fabric covered trim tab surface on the trailing edge of the left elevator. The name of the person that performed the trim tab modification could not be determined. The silver painted trim tab measured approximately 5 inches wide by 20 inches long.

No maintenance records were located for the ultralight during the course of the investigation.

WRECKAGE AND IMPACT INFORMATION

The accident site was located on level grassy terrain in a cow pasture within the Kelly Burt Ranch, approximately a mile north of the airport. Ground signatures at the accident site indicate that the ultralight impacted the ground in a slight right turn in a nose low attitude on a measured heading of 315 degrees. The ultralight came to rest in the inverted position facing opposite the direction of flight.

A 30 foot linear imprint corresponding to the leading edges of both wings was found at the initial point of impact. The right side of the imprint was slightly deeper than the left. The damage to the leading edge of the right wing was more pronounced that the damage on the left wing leading edge.

Both fabric covered wings remained partly attached to the fuselage. Both "full-span" ailerons remained attached to the wings. The tail assembly remained attached to the tubular tailcone. Damage to the rudder, vertical stabilizer, horizontal stabilizers and elevator was minimal.

The nose section of the ultralight, which included the rudder pedals, instrument panel, the plexiglass "cocoon" cockpit, and the pilot's station were destroyed by impact damage. Two shallow craters, each approximately 2 square feet, were found at the initial point of ground impact. The engine was found adjacent to one and chips of paint and plexiglass identified as part of the nose of the ultraligt were found in the other.

Paint transfers, chaffing and rubbing found on the rudder and right elevator indicated that the elevator trim tab had separated from the trailing edge of the left elevator prior to ground impact. The mounting for the outboard bracket, supporting the outboard end of the trim tab, was found to be loose. Paint transfer and associated chaffing found on the trailing edge of the elevator indicated that the bracket had been loose prior to the accident. No sign of blockage or obstruction were found that could have impeded the movement of the elevator or rudder.

Aileron control continuity was confirmed from both control surfaces to the control stick in the cockpit. The rudder pedals were destroyed by impact; however, rudder cable continuity was established from the cockpit to the rudder. Examination of the elevator control system revealed that that all connections, with the exception of the trim tab on the left elevator, remained attached and continuity was established. Likewise, continuity was established from the engine controls in the cockpit, to the carburetor.

The Rotax engine separated from the airframe but remained attached to the engine control cables and lines. The carburetor was found separated from the engine. Engine continuity was established by turning the propeller by hand. The 3-blade fixed pitch propeller remained bolted to the crankshaft. One blade was undamaged, another one was fractured approximately 12 inches from the tip, and the third blade was fractured within 2 inches outboard or the hub. The outboard portion of the third blade was shattered and splintered in several pieces. None of the blades separated from the hub.

The ultralight was equipped with dual 5-gallon plastic fuel tanks. Both fuel tanks were compromised during the impact sequence. Automotive gasoline was found in the fuel lines as well as in the rubber hand primer pump. The grass in the area forward of the initial point of impact revealed evidence of chemical burns as result of the fuel sprayed from the compromised fuel tank.

MEDICAL AND PATHOLOGICAL INFORMATION

An autopsy and toxicological tests were ordered and performed. The autopsy was performed at the Autopsy Suite of the Saint Joseph Regional Health Center in Bryan, Texas, on October 24, 1998. No evidence of an acute myocardial infarct was found. Toxicological findings were negative.

ADDITIONAL DATA

The wreckage of the ultralight was released to the owner's representative upon completion of the field portion of the investigation.

NTSB Probable Cause

The pilot's loss of control as result of the partial separation of the elevator trim tab resulting in the inability to maintain aircraft control. A factor was the improper design and installation of the elevator trim tab.