Reno, NV, USA
N126PS
Schleicher ASW-20
The glider entered a stall and spin while attempting a return to runway maneuver following an overload failure of the towrope in the takeoff initial climb. During takeoff, the towrope between the tow plane and glider broke while the glider was about 300 feet above ground level. The glider pilot reversed course and attempted to return to the departure runway. The tow plane pilot said that when he looked back the glider was in a left turn with its heading passing through 030 degrees when the right wing suddenly dropped downwards and the glider appeared to descend vertically, nose down. The glider made about 1/2 a clockwise rotation, nose down, before it impacted the desert. The Safety Board Materials Laboratory examination of the towrope and safety link revealed: 1) The towrope was worn by abrasion and sunlight at the glider connection end, which had substantially reduced the strength of the rope at the failure location; 2) the worn end of the rope was about 60 percent weaker than the unworn end; 3) the towrope failed due to overloading at the knot; and 4) the unworn end of the towrope and the safety link met the tensile strength required by 14 CFR 91.309. The rope area around the knot connecting the towrope to the safety link was wrapped in a protective layer of duct tape, and therefore, the rope condition at the failure point could not be easily examined by the pilot during a towrope preflight inspection. Examination of the glider revealed no evidence of preimpact malfunction or failure of the flight control system. The tow plane pilot reported that there were gusty winds and turbulence present at the time. The ASW-20 Flight Manual includes a section titled "Dangerous Flight Attitudes," which contain a number of cautionary statements and warnings pertaining to stalled flight. Full control deflections will result in wing dropping, whereas full-deflected controls in opposite directions with stick pulled completely back will case rapid wing dropping. Initiated from turning flight the wing dropping is more rapid than from level flight. Full deflections of opposite rudder and aileron deflections will lead to a spin. The Federal Aviation Administration produced "Glider Handbook, AC 80-83-14" contained a very brief section about towrope inspection and essentially stated that the rope should be inspected for excessive wear without defining what that means.
HISTORY OF FLIGHT On May 8, 2004, at 1600 Pacific daylight time, a Schleicher ASW-20, N126PS, collided with terrain during an uncontrolled descent following separation of the towrope after takeoff at the Air Sailing Gliderport, 21 miles north of Reno, Nevada. The private pilot-owner was operating the glider on a local flight under the provisions of 14 CFR Part 91. The glider pilot was fatally injured, and the glider was destroyed. Visual meteorological conditions prevailed, and no flight plan had been filed. The tow plane pilot reported in a written statement that he was towing the glider on the runway heading of 210 degrees and was about 300 feet above ground level (agl) when he felt the towline break. He initiated a left turn, towards a heading of 180 degrees, and looked over his left shoulder to observe the glider about 100 yards behind him. The glider was in a left turn with its heading passing through 030 degrees when the right wing suddenly dropped downwards and the plane appeared to descend vertically, nose down. The glider made about 1/2 a clockwise rotation, nose down, before it impacted the desert. PERSONNEL INFORMATION A review of Federal Aviation Administration (FAA) records from Oklahoma City, Oklahoma, revealed that the pilot held a private pilot certificate issued on June 29, 1996, with ratings for single engine land and glider aero tow. The pilot held a second-class medical certificate issued on November 19, 2002. It had the limitation that the pilot must wear corrective lenses. Examination of the pilot's logbook revealed that he had 917.6 hours of total flight time, 497.7 hours of glider time, and 97.3 hours of time in the ASW-20. Within the last 90 days the pilot had 4.9 hours in a single engine airplane, 2.1 hours in various gliders, plus 1.3 hours in an ASW-20. Within the last 30 days he had 3.9 hours in a single engine airplane, 1.1 hours in a glider, and 0 hours in a ASW-20. AIRCRAFT INFORMATION The Schleicher ASW-20 is a composite constructed, single place high performance glider, and was issued an experimental airworthiness certificate in the exhibition and racing category by the FAA. Examination of the maintenance logbook revealed that an aircraft annual inspection was documented on March 9, 2004, at a total aircraft time of 2,314.8 hours. The Flight and Operations Manual for the ASW-20 specifies that the max gross weight is not to exceed 1,000 pounds. The manual also specifies that the safety link in the towing line be rated at 1,320 pounds. A fellow glider pilot stated that he had helped the pilot perform a positive control check prior to the flight. The ASW-20 Flight Manual includes a section titled "Dangerous Flight Attitudes." In that section there are a number of statements pertaining to stalled flight. "Even in stalled flight attitude (the vario will read 1.5 to 2 m/s sink in calm air, that is 300 to 400 feet per minute) ailerons and rudder work in the usual manner, as long as only half control deflections are applied. Full control deflections result in light wing dropping, whereas full-deflected controls in opposite directions with stick pulled completely back will case rapid wing dropping. Initiated from turning flight wing dropping is more rapid than from level flight. The loss in altitude for wing dropping is about 20m (60 feet)." "Full deflections of rudder and aileron will cause wing dropping, opposite rudder and aileron deflections will lead to a spin. Wing dropping as well as spinning are terminated with the (German) standard procedure (opposite rudder and elevator neutral, see page 22)." The ASW-20 Flight Manual states the following about aero tow. "Maximum aero tow speed is 175 km/h (94 knots, 109 mph). Tested lengths for manila or nylon tow-ropes are with in the 25-60m (80-200 feet) range. For tows behind 180 hp or even stronger tow planes the towrope should be at least 40 m (130 feet) long. For takeoff roll flap position No. 2 (-6 degrees) is recommended. After about 50 km/h (25 knots) have been gained, flap position No. 3 (0 degrees) or even No. 4 (+9 degrees) is applied for earlier liftoff." The tow plane was a Piper PA-25-235, N4625Y, operating a Lycoming O-540 engine that produces about 260 horsepower. METEOROLOGY The tow plane pilot reported that the wind at the time of the accident was gusting from the southwest, roughly along the runway heading of 210 degrees, varying 40 to 50 degrees. A witness that was soaring above the gliderport at the time of the accident said that during his takeoff tow the "conditions were very turbulent with up and down drafts." The closest aviation weather reporting station is Reno Airport, which is 21 miles south of the Air Sailing Gliderport. At 1556, the Reno Airport reported winds from 290 degrees at 15 knots with gusts to 22 knots; visibility 10 statute miles; temperature 23 Celsius; dew point 1 Celsius; altimeter setting was 30.03 inHg; and the clouds were few at 18,000 feet, and broken at 25,000 feet. WRECKAGE AND IMPACT INFORMATION The wreckage was located about 500 yards southwest of runway 21 at the Air Sailing Gliderport. The terrain was flat desert populated with shrubs and sagebrush. The debris field was confined to the area immediately surrounding the aircraft wreckage. The left and right wings were fractured at the spar/wing root area joining at the fuselage and lay in place aligned with each other. Both wings were split open along their leading edge and the spoilers on both wings were deployed between halfway and full. The cockpit was centered between the wings and was inline with the tail boom. The cockpit fuselage fiberglass was splintered and crushed, twisted about its longitudinal axis, lying on its left side. The flight control linkages and connections were examined on scene. All connections were safety pined. All but one L'Hotellier ball and socket connector was connected in place. The free L'Hotellier socket had a semicircular indentation on the socket cup lip and the safety pin was in place. All flight control surfaces were located at their appropriate positions on the wings and tail. The flap extension was measured at 29 degrees in the negative direction (up). MEDICAL AND PATHOLOGICAL INFORMATION The Washoe County Coroner performed an autopsy of the pilot. The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, performed toxicological analysis from tissue and blood samples obtained during the autopsy. The toxicological analysis results were negative for carbon monoxide, cyanide, volatiles, and tested drugs. TESTS & RESEARCH The Towrope The towrope was collected by local law enforcement and supplied to the Safety Board investigator. The rope consisted of a long section of dirty-white tightly braided rope, 5/16 inches in diameter, and a short section (about 4 feet long) of yellow rope with red tape markers equally spaced along its length. The towrope was subsequently measured by the Safety Board investigator in its untangled state and found to be 197.5 feet in length. Photographs of the long length of dirty-white tow rope show one end (the tow plane attachment end) with the rope passing through a metal ring; the rope was protected by a length of black plastic tube, and the rope, ring, and plastic tube interface wrapped with gray duct tape. The opposite rope end (glider attachment end) had an unevenly frayed end with gray duct tape wrapped around the rope starting about 1 inch up from the end and extending about 6 inches. In the mid section of the rope two knotted areas were observed in the photographs; one was a compact knot with numerous loose loops and the other was a section of about two 10-foot-long parallel lengths lashed together. The dirty-white rope was measured as 5/16 inch in diameter. The outer braiding of the rope appeared dirty and was consistently observed with rough "fuzz" along its length. A 4-foot-length yellow nylon braded rope with alternating red stripes evenly spaced in four sections was used as the safety link. A metal ring was at one end of the safety link and was attached by a rope loop splice with a clear plastic sheath around the loop. A couple inches up from the metal ring was a red plastic golf ball sized whiffle ball that the rope passed through the center of. At the opposite end of the safety link was a spliced loop protected with a clear plastic sheath. Attached to the loop was a threaded nut closed d-ring attaching a round metal ring. Attached to the metal ring was a 5-inch length of dirty-white rope wrapped tightly with gray duct tape. This section of gray duct tape matched up precisely with the remaining duct tape on the separated end of the towrope. Laboratory Examination and Load Testing of the Tow Rope and Safety Link The towrope and safety link were submitted to the Safety Boards Materials Laboratory for examination. Examination of the tow rope revealed a braided construction consisting of 16 strands, and each strand consisting of a large number of fine filaments. The towrope was uncoiled from its "as received" condition and examined. The towrope was a single piece and exhibited a gradual change in appearance between the extreme ends. The towrope adjacent to the separated end was larger in diameter and filaments on the outer surface of the strands were broken, giving it a fuzzy appearance. The fuzzy appearance is consistent with exposure to abrasive wear and sunlight. The towrope adjacent to the towing aircraft end was clean-white with no abrasions or surface fuzz. Examination of the towing aircraft connection revealed a knot with a double loop around an oval ring. A round ring was linked with the oval ring producing what is commonly referred to as a "connecting pair." The knot was identified as a bowline. Examination of the safety link revealed that the connection end consisted of a round ring to which the towrope was originally connected, and a screw type connector. Examination of the round ring and the connector revealed a loss of material and score marks consistent with it being dragged along the ground and patches of light surface rust. The scoring had rounded off the corners of the hexagonal nut portion of the screw type connector. The rope portion of the safety link was also of braided construction and consisted of two eyes, each protected in a plastic tube and looped through the connectors at each end, a spliced length adjacent to each eye, and an unspliced section roughly in the middle. At the start of the splice for the glider connection a hollow plastic ball with holes through its skin, commonly referred to as a "whiffle ball" was installed. Examination of the "connecting pair" of rings at the glider connection revealed scoring, not as severe as that observed on the towrope connection, and patches of light surface rust. The safety link and three portions of the towrope were tensile tested to failure. The three towrope portions consisted of a plain length of towrope adjacent to the separated end (identified as "separated end"), a length including the towing aircraft connection (identified as "towing aircraft connection"), and a plain length of towrope adjacent to the towing aircraft end (identified as "towing aircraft end"). The separated end failed under a 724-pound load, the towing aircraft connection failed at the bowline knot under a 1,276-pound load, the towing aircraft end failed under at load of 1,797 pounds, and the safety link failed under an 808-pound load. The towrope and the safety link were found to comply with FAA towrope strength guidelines for the weight of the glider; however, the tensile strength of the towrope at the worn glider attachment end was about 60 percent less than the tested tensile strength of the unworn rope section. The worn condition of the towrope portion that was attached to the safety link by a knot and wrapped in duct tape was consistent with the wear and condition of the exposed severed end of the towrope. Tensile testing revealed that a bowline knot reduces the strength of the rope by about 29 percent. The entire laboratory report is contained in the official docket of this investigation report. ADDITONAL INFORMATION Federal Aviation Regulation (FAR) Part 91.309 states the following regarding towrope strength requirements: The towline used has breaking strength not less than 80 percent of the maximum certificated operating weight of the glider, and not more than twice this operating weight. However, the towline used may have a breaking strength more than twice the maximum certificated operating weight of the glider if- (i) A safety link is installed at the point of attachment of the towline to the glider with a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider and not greater than twice this operating weight; (ii) A safety link is installed at the point of attachment of the tow line to the towing aircraft with a breaking strength greater, but not more than 25 percent greater, than that of the safety link at the towed glider or end of the towline and not greater than twice the maximum certificated operating weight of the glider; Emergency Landing Strip According to the tow plane pilot, there is an emergency landing strip ahead and to the right of runway 21 at the Air Sailing Gliderport. It was the tow pilot's opinion that the glider pilot could have made it to the emergency landing strip after the tow line broke. FAA Glider Flying Handbook (FAA-H-8083-13) Returning for a downwind landing on the departure runway after a tow line release is a practice utilized by glider pilots and endorsed as an option by the FAA Glider Flying Handbook. "If an inadvertent release, towrope break, or a signal to release from the tow plane occurs after the tow plane and glider are airborne, and the glider possesses sufficient altitude to make a 180 (degree) turn, then a downwind landing on the departure runway may be attempted. The 180 (degree) turn and downwind landing option should be used only if the glider is within gliding distance of the airport or landing area. In ideal conditions, a minimum safe altitude of 200 feet above ground level is required to complete this maneuver safely. Such things as a hot day, weak towplane, strong wind, or other traffic may require a greater altitude to make a return to the airport a viable option."
the pilot's failure to maintain an adequate airspeed margin while performing a return to runway maneuver, which led to a stall and spin. Factors in the accident were: 1) the deteriorated condition of the glider towrope, which resulted in towrope failure during a critical phase of the tow; 2) the duct tape covering over the abraided portion of the failed rope end that made inspection of the rope difficult; and, 3) the gusty winds and turbulence.
Source: NTSB Aviation Accident Database
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