FTW99FA265

The homebuilt airplane (TT 114.3 hours & 22.4 hrs since last condition inspection) was destroyed following an in-flight separation of the left wing in level flight and the subsequent uncontrolled flight into terrain. The two-place (tandem) seating, open cockpit, low wing, fabric covered airplane incorporated a tubular steel welded fuselage and empennage, with wooden wings. The left wing separation points were at the wing root where the wooden main wing spar and rear wing spar passed through the tubular brackets of the fuselage. Examination of the failed surfaces revealed that the left wing separated from the aircraft in a predominately upward direction. The main spar was the first to separate in an upward direction. The rear spar then separated in an upward direction with a slight movement towards the rear. The probable cause of the separation was the choice of basswood for the spars instead of the specified spruce. According to the designer, aircraft grade spruce is the only wood specified for the spars. Builder records indicated the use of basswood for spar construction. Examination confirmed the wood spars were basswood. Basswood is considerably weaker and less stiff than spruce. The FAA Advisory Circular 43.13-1B/2A, Chapter 1, Wood Structures, Table 1-1. Selection and Properties of Aircraft Wood, indicates that spruce is excellent for all uses and is considered as the standard by the FAA. Table 1-1 does not list basswood as a selection of aircraft wood. Chapter 1 Paragraph 1-41 states in part: The type of wood used is critical to the structural strength of the aircraft.

History of flight

On September 25, 1999, at 1715 central daylight time, a Carter Spacewalker II homebuilt experimental airplane, N235FC, was destroyed when it impacted the terrain following an in-flight separation of the left wing in level flight at the Montgomery County Airport near Conroe, Texas. The airplane was registered to a private individual and operated under 14 Code of Federal Regulations (CFR) Part 91. The commercial pilot and the passenger received fatal injuries. Visual meteorological conditions prevailed for the personal flight, and a flight plan was not filed. The local flight originated from the Montgomery County Airport at 1712.

The owner reported that when the preflight was performed, the fuel tank was 1/2 full (maximum capacity 18 gallons). The owner and pilot performed two takeoff and landings on runway 14 at the Montgomery County Airport. Upon taxiing to the fixed base operator (FBO) ramp, the pilot moved to the aft seat and the passenger boarded the front seat. The owner assisted the passenger in securing his three point safety harness and briefed the passenger to remain clear of the cockpit flight controls. The pilot taxied the airplane to runway 14 for departure. Following the departure, the airplane entered a left turn, circled in a climbing turn, and flew back over the airport. The owner stated that the airplane was in level flight on about a 200 degree magnetic heading, midfield of the airport, at 1,500 feet agl when the "left wing broke away and [the] fuselage did [a] snap rotation to left." The engine was at "full power and continued to run until the impact."

The unicom operator, who witnessed the accident, reported that the "plane began to rock slightly from left to right. The plane then pitched up and then down again. At that time, the wing separated from the fuselage and the plane went into a spin." The spin occurred from about "1,000 feet agl."

Another witness stated that the "right wing folded straight up against the fuselage and sheared away. The plane went into a spin and crashed into the south end of the field."

Another witness reported that the airplane "appeared flying level or slight climb to south at an est[imated] alt[itude] of 500 [feet] agl. Heard loud noise of wing separation. Saw the wing flutter horizontally, then spiral away from aircraft." The engine "rpm's went to what seemed to be max[imum]. The airplane went into a tight corkscrew making 3-4 or 5 turns and impacted."

Personnel information

A second class medical, with a limitation for corrective lenses, was issued to the pilot on February 1, 1999. The available FAA records revealed that the pilot had accumulated 4,500 hours of flight time. He held commercial privileges in airplane single-engine land and multi-engine land with an instrument rating. He held private privileges in single-engine sea airplanes. The pilot held a mechanic certificate with airframe and powerplant ratings.

The owner stated that the pilot had approximately 15 hours in the make and model of the accident aircraft. No additional information on the pilot's flight time was obtained.

Aircraft information

The Spacewalker II was designed by Anglin Engineering of Rutherfordton, North Carolina. The two-place (tandem) seating, open cockpit, low wing, fabric covered airplane incorporated a tubular steel welded fuselage and empennage, with wooden wings. A copy of the plans to build a Spacewalker II were sold by Anglin Engineering to the builder of the accident airplane.

The designer's specifications indicated a maximum gross weight of 1,200 pounds (lbs) with a basic empty weight of 700 lbs. Builder records for N235FC indicated a basic empty weight of 898 lbs, and a maximum gross weight of 1,300 lbs. Utilizing the builder's basic empty weight, the pilot's weight (214 lbs) on his last medical certificate, the passenger's estimated weight (175 lbs), with an estimated 8 gallons of fuel (48 lbs), the gross weight of the aircraft at the time of the accident was 1,335 lbs.

According to the builder of the accident airplane "there are four basic components that make up the spar. The first being a solid wood, I used a material known as basswood. The second item would be marine plywood followed by aircraft grade plywood. All parts were bonded together with a two part adhesive (T-88)." According to the designer, aircraft grade spruce wood was specified in the plans for the wing spars and the main wing spar was designed to carry 7 G's with a safety margin.

According to the designer, aircraft grade spruce is the only recommended wood for the main spar and the rear spar. The designer further stated that the welded steel fuselage tubing that forms the main and rear spar carry through brackets is designed oversized vertically, which permits the builder to set the angle of incidence for the wings. Once the angle of incidence is determined and set, the oversized area is intended to be filled with wedges of wood glued to the spar so that no space remains within the tubular bracket. There was no physical evidence found that the space had been filled on the accident aircraft. However, the designer indicated that he was aware of other aircraft on which the space had not been filled and that inspection of these aircraft revealed no problems.

In April 1991, a 115 horsepower Lycoming O-235-C1 engine, overhauled for experimental use only, with a 2-bladed Sensenich propeller, was installed in the airframe. On December 5, 1991, the aircraft was issued the FAA special airworthiness certificate in the experimental category under CFR Part 21.191.

In September 1993, the aircraft was disassembled for transport in an enclosed truck when it was sold to an individual in California. In May 1996, the aircraft was disassembled for trucking when it was sold to an individual in Montana. In June 1998, the aircraft was assembled from container shipment when it was sold to an individual in Florida. In 1999, the current owner purchased the airplane and flew it to Texas.

The last condition inspection was performed on June 30, 1999, by the accident pilot/mechanic. At the time of the inspection, the total aircraft time was recorded as 91.9 hours, with a tachometer reading of 39.9 hours. The tachometer reading at the accident site was 62.3 hours. By subtracting 39.9 hours from 62.3 hours, it was determined that the aircraft had flown 22.4 hours since the last inspection. By adding 91.9 hours and the 22.4 hours, the total time on the aircraft was calculated as 114.3 hours. These calculations are in agreement with the owner, who stated that the airplane had flown "about 22 hours in the previous 3 months since his ownership, and the total aircraft time was about 115 hours."

During a personal interview, conducted by the NTSB investigator-in-charge (IIC), the owner stated that numerous people had flown the airplane since his ownership. The owner and pilots, who had flown in the airplane and responded to the NTSB IIC inquiry, stated that to their knowledge, the airplane did not have a history of aerobatic maneuvers. One pilot stated that the airplane was involved in a "hard landing" the week prior to the accident, that "damage ensued", and that the owner was "engaged in repairing a bent landing gear fitting and the aircraft was on jacks and unflyable for the week prior to the accident."

The owner stated that about 2 weeks before the accident, during taxi at the Montgomery County Airport, he noted that the left wing was a few inches below the right wing. Upon examination of the left main landing gear, he found that a bracket needed repairing. Subsequently, he repaired the left main landing gear bracket; however, an entry had not been made in the maintenance records.

One of the pilots, who had flown in the accident airplane, reported observing the airplane undergoing maintenance midday Friday, September 24, 1999. The main