NTSB Factual Report

HISTORY OF FLIGHT

On August 27, 1994, at 1310 central daylight time, a Schweizer SGS 1-34R, N1132S, collided with trees and terrain, following an in-flight separation of the left wing while maneuvering, near Maylene, Alabama. The private pilot was fatally injured. The glider was destroyed. The aircraft was operated under the provisions of 14 CFR Part 91 by the Birmingham Soaring Society, Inc. Visual meteorological conditions existed at the time, and no flight plan was filed for the local, personal flight. The flight originated at the Flying X Ranch, in Montevallo, Alabama, about 1240.

A flying club pilot, Mr. Jerry Linley, observed the accident pilot, Mr. Jack Dunwoody, as he arrived at the Flying X Ranch, prior to the accident flight. They discussed the weather conditions, and the availability of the club's Schweizer SGS 1- 34R. The aircraft was available, and Mr. Dunwoody performed his preflight inspection. He also commented that he would review the aircraft performance speeds. During general conversation, Mr. Dunwoody was observed to be in good health, with no visible signs of stress or preoccupation. Mr. Linley also observed Mr. Dunwoody's takeoff. The launch proceeded smoothly, and the takeoff and initial climb appeared normal. He last observed the aircraft after the release from the tow aircraft, but he did not witness the accident.

Several witnesses were located following the accident. One witness reported that he walked out of his back door, and saw the glider, which appeared to be in normal flight. From his vantage point, the glider appeared to be in a left turn, and a shallow bank. Seconds later, he heard a loud noise, and the "right" wing came up towards the fuselage. He stated that the noise sounded like a board breaking when stepped on. He saw pieces falling from the aircraft, but was unsure if the right wing separated from the airframe. He saw some clouds in the area, but not in the immediate vicinity of the glider. He never saw the glider penetrate any clouds at any time.

Another witness was inside a building, and heard a loud, cracking sound. He stepped outside, and saw an aircraft with one wing, spiralling nose down. The aircraft went behind some trees, and he heard a crashing sound.

Another witness was standing outside, when she saw the aircraft go by. She stated that she saw he aircraft go into the clouds, and then she heard a loud noise. She saw a wing "flying off" the airplane, followed by other "particles."

PERSONNEL INFORMATION

An examination of the accident pilot's logbook revealed the following: The pilots total flying time was about 53 hours (132 flights), including .8 hours in the SGS 1-34R (2 flights). His first logged glider flight occurred on January 11, 1992. The aircraft that was utilized during his initial phase of training was a Schweizer SGS 2-33. His initial solo flight occurred on August 9, 1992, in an SGS 2-33. His first attempt at the private pilot practical examination took place about one year later, on August 28, 1993. The pilot failed his first attempt at the practical examination, and logbook entries show that after several additional flights, the practical examination was again taken on September 11, 1993, with satisfactory results. His first flight in a Schweizer SGS 1-34R was performed on May 21, 1994, which included .5 hours of flight time. The second flight in the SGS 1-34R (which was the last 1-34R flight prior to the accident flight) occurred on June 19, 1994, and included .3 hours of flying time. Both of these flights took place in N1132S. In the remarks section of the logbook entry of May 21, the entry indicated "gusty, some thermals," and on the June 15 flight, the remarks included "No thermal activity."

Mr. Billy Singleton, who is a designated pilot examiner, flew both practical examination flights with the accident pilot. He reported that the first attempt was graded unsatisfactorily due to difficulties with landing accuracy. He reported that additional instruction was performed, emphasizing landing practice. The second attempt at the practical examination was satisfactory. He also recalled about 30 minutes of ground instruction with Mr. Dunwoody about the flight characteristics of the SGS 1-34R. This instruction was not associated with any particular flight. Mr. Singleton could not recall any unusual tendencies shown by Mr. Dunwoody regarding airwork flying ability.

During the 90 day period prior to the accident, the pilot had logged 8 flights, with a total flying time of about 3.2 hours. During the 30 day period prior to the accident, he logged 3 flights, all on August 7, 1994, and all in the SGS 2-33.

The accident pilot did not possess any ratings or certificates other than "private pilot-glider aero tow." Additional information on the pilot is included in the section titled "First Pilot Information."

AIRCRAFT INFORMATION

Information on the aircraft is included in this report at the section titled "Aircraft Information."

Leslie E. Schweizer, Vice President, Engineering and Quality Control, Schweizer, Aircraft Corporation, participated in the investigation during the follow up examination of the wreckage. He reported that the limit load factor for this glider was +5.33 g, and the ultimate load factor was +8.0 g. He also stated that this glider is considered a high performance glider, with a high design speed, and a low stall speed. Therefore, the capability exists to develop large load factors beyond the design limits, in a maximum unchecked maneuver above the maneuvering speed. The SGS 1-34R has a design speed of 150 mph, a maneuvering speed of 83 mph, and a stall speed of 36 mph. The load factor that can be developed in a maximum maneuver, at 135 mph (placard red line speed, or .9 X design speed) is +14g.

METEOROLOGICAL INFORMATION

Weather information for Birmingham, Alabama (BHM) is included in this report at the section titled "Weather Information."

One of the pilots in the Birmingham Soaring Society was flying an instructional flight, in the vicinity of the crash site of N1132S, at approximately 1330, on the day of the accident. At the time of the flight, he was not aware that an accident had occurred. Weather conditions at the time of the takeoff included calm surface winds, and a temperature of 90 degrees F. Estimated in flight visibility at 2,500 feet was 7 to 10 miles, in haze. Winds aloft were from a southeasterly direction at about 10 miles per hour. Turbulence was evident, but not greater than would be expected for August. After releasing from the tow plane, average climb rates of 200 to 300 feet per minute were common, with isolated areas of 500 feet per minute lift observed. He estimated the scattered cloud layer to be about 4,500 to 5,000 feet during the flight. He did experience isolated areas of thermal activity which required full control deflection to maintain aircraft attitude.

WRECKAGE AND IMPACT INFORMATION

The main wreckage was located in a wooded area, about two miles northwest of the departure airport (Flying X Ranch). The left wing was found on a hill, about 1,000 feet due west of the main wreckage. In the area between the left wing and the main wreckage, two sections of left wing skin, and a trailing edge extrusion from the left wing, were found. A wreckage distribution diagram is included as an attachment to this report.

The main wreckage came to rest near the trunks of several large trees. Several large, freshly broken branches were found adjacent to, and on top of, the wreckage pieces. The nose and cockpit sections were found in a crater, which was about 2 feet deep, and 4 feet in diameter. The nose and cockpit were crushed in an aft direction, to the bulkhead behind the pilot seat. Flight control continuity was confirmed from the cockpit area aft, to the rudder and elevator.

The left wing was found to have separated from the aircraft at a point approximately 8 inches outboard of the root rib. The main spar fractures consisted of upward, and aft bending signatures. The spar reinforcing strips, which are attached to the forward side of the main spar caps, were bent in an aft direction. The outboard section of the left wing was bent in an upward direction, at a point approximately aligned with the inboard edge of the left aileron. On the upper, outboard side of the wing skin, there was a spanwise transfer mark, red in color, which matched the red paint color on the tail cone. This aircraft was equipped with optional wing stiffener panels. These panels consist of thin sheet metal, bent to form corrugations, and bonded to the inside of the upper wing skins. The panels run spanwise, from rib to rib, and are located ahead and behind the main spar. According to the glider manufacturer, one of the features of these panels is that they will cause the wing skins to buckle at the end of the panel (at each rib), and take a permanent set just above wing limit load. On the top surface of the left wing, skin wrinkles were observed at every station where the stiffener panels were located.

The main spar carry through plates remained attached to the fuselage, with the mount pins intact and secured. At the center of the structure, where the spar cap and reinforcing strips stop, each main spar consists of a forward and aft .25 inch plate to carry the load. Both the left and right wing plates in this center region had bowed and yielded. According to the manufacturer, these plates never yielded in static tests where the +8.0g ultimate load was applied.

The right wing was found with the main wreckage. It was fragmented, but the recovered sections were all within the same immediate area as the main wreckage. Most of the wing skin was pulled away from the wing structure. The upper spar cap was bent and buckled, and the reinforcing strips were bent aft. There were numerous areas of tree bark transfer marks on the outer areas of the right wing, with associated areas of crushing signatures.

All major structural areas of the empennage were found with the main wreckage. All empennage areas were crushed and shredded, with bark colored transfer marking evident on all surfaces.

The main gear tire and wheel were found with the main wreckage. There was freshly shredded wood imbedded in the wheel brake area. According to the manufacturer's representative, the SGS 1-34R landing gear is held in the retracted position by a helper spring to balance the weight, and secured by a latch on the retraction handle. An examination of this latch pin on the wreckage revealed areas of wear. The manufacturer's representative reported that the landing gear will deploy (extend) under high g loading if the latch pin is worn, as the spring cannot overcome the additional g-load on the wheel.

MEDICAL AND PATHOLOGICAL INFORMATION

A post mortem examination of the pilot was performed by Dr. Joseph H. Embry, M.D., State Medical Examiner, Alabama Department of Forensic Sciences.

TESTS AND RESEARCH

The upper section of failed spar cap material, which was removed from the separated left wing, was sent to the National Transportation Safety Board Materials Laboratory for examination. The examination revealed that all fracture surfaces on the examined part were consistent with overstress separations.

ADDITIONAL INFORMATION

The wreckage was released to:

Les Sychak COMAV Managers, Inc. P.O. Box 72647 Marietta, Georgia 30007-2647.

NTSB Probable Cause

THE PILOT EXCEEDING THE DESIGN STRESS LIMITS OF THE AIRCRAFT, RESULTING IN AN OVERLOAD FAILURE OF THE WING SPAR, AND SEPARATION OF THE LEFT WING FROM THE AIRCRAFT. A FACTOR WAS THE PILOT'S LACK OF TOTAL FLYING EXPERIENCE IN THIS MODEL OF AIRCRAFT.