Aguila, AZ, USA
N7729S
Schweizer SGS 1-26D
The glider descended into flat terrain during the initial climb in an aero tow. After obtaining takeoff acceleration, the glider became airborne in a normal trailing position behind the tow plane. When the tow plane reached an altitude of about 15 to 30 feet agl, the glider began to pitch nose-high, and the tow pilot felt the airplane's tail being pulled upward. The glider continued to pitch upward, and climbed about 150 feet agl before the tow rope broke. The glider pitched over in a slight nose-low attitude, and began a shallow turn to the runway. While in the turn, the glider's bank angle increased and the nose dropped. The glider's airspeed became very slow, and it continued to turn, eventually spiraling into the ground in a 50 to 60 degree nose-low attitude. A postaccident examination of the glider, including a detailed examination of the control system, revealed no anomalies that would have precluded normal operation.
HISTORY OF FLIGHT On May 3, 2006, about 1430 mountain standard time, a non-powered Schweizer SGS 1-26D glider, N7729S, descended into terrain during the initial climb from Sampley's Airport, Aguila, Arizona. The pilot/owner was operating the glider under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, sustained fatal injuries; the glider was substantially damaged. The local personal flight was originating from Aguila at the time of the accident. Visual meteorological conditions prevailed, and a flight plan had not been filed. A National Transportation Safety Board investigator conducted a telephone interview and received a written statement from the pilot of the airplane that was towing the accident glider. He stated that he was flying a Piper Pawnee, which he frequently utilized to conduct towing operations from Aguila. Prior to departure, he and the accident pilot discussed the proposed tow procedure and release point. The tow was started by both pilots using a series of hand signals and rudder movements to convey that they were prepared for a departure on runway 17. The tow pilot reported that the takeoff acceleration was normal, and with utilization of a rearview mirror, he observed the glider become airborne in a normal trailing position. As the tow plane accelerated to about 50 miles per hour (mph), he became airborne and initiated a gradual climb at 70 mph. The tow plane progressed about 800 to 900 feet down the runway and was at an altitude of about 15 to 30 feet above ground level (agl), when the tow pilot felt as if the tail was being pulled upward. He glanced again in the mirror and noticed that the glider was climbing upward, out of his range of vision. The tow pilot further stated that the airplane's tail continued to be pulled upward with such a strong constant force that he had to exert great effort to manipulate the control stick aft. Despite his efforts, the airplane's attitude remained in a 10- to 15-degree tail-high [nose-low] pitch for about 3 seconds. The tow pilot estimated that the glider climbed about 100 to 150 feet agl and then he felt a quick release of pressure from the control stick, consistent with the tow rope breaking. The tow plane pitched nose up and the tow pilot began a shallow right turn keeping his eyes affixed on the glider. The tow pilot observed the glider pitch over in a slight nose-low attitude and begin a shallow turn to the west, which he thought was consistent with the glider pilot turning back to the runway to land. After turning about 45 degrees, the glider's bank angle increased and the nose dropped. The glider's airspeed became very slow and it continued to turn eventually spiraling into the ground in a 50- to 60-degree nose-low attitude. The glider bounced backward about 15 feet before coming to rest east of the runway centerline. The tow pilot noted that the runway was about 3,000 feet long. He added that he thought the glider would have been able to land on the runway after the towrope broke. PERSONNEL INFORMATION A review of the Federal Aviation Administration (FAA) Airman and Medical Records disclosed that in August 1975, the pilot was issued a private pilot certificate, with a glider aerotow rating. The pilot did not hold a current FAA issued medical certificate. According to 14 CFR Part 61.23 (b), Operations Not Requiring a Medical Certificate, a person is not required to hold a valid medical certificate if they are exercising the privileges of a pilot certificate with a glider category or balloon class rating. The pilot's spouse provided a Safety Board investigator copies of the pilot's personal flight logs, which consisted of excerpts from 2001 to the accident date. The logbooks revealed that the pilot had accumulated 738.14 hours of total flight time, of which about 25 hours was logged in the accident glider. After two flights on August 26, 2004, the logbook showed no entries until April 11, 2006, where the pilot logged three flights totaling 32 minutes. The remarks section of the logbook for the last three flights indicated that a flight review was completed, as well as a 1-hour ground school. The last entry (aside from the accident flight) was dated May 01, 2006, where the pilot logged 3.08 hours. AIRCRAFT INFORMATION The glider was a Schweizer SGS-1-26D, serial number 429, manufactured in 1968. A copy of the most recent glider logbook was provided to a Safety Board investigator; the location of previous logbooks were unknown. The glider underwent its last annual inspection on April 28, 2006, at a total time of 1,242 hours. The total time of the glider at the time of the accident was unknown. The glider was 21.54 feet in length, had a wingspan of 40 feet, a wing area of 160 square feet, equating to an aspect ratio of 10. The glider's maximum gross weight was 700 pounds. The glider was equipped with ailerons and a dive brake mechanism (spoiler). According to the Schweizer 1-26 Sailplane "FLIGHT-ERECTION-MAINTENANCE" Manual for Models A through E, a speed of 50 to 60 mph is recommended for performing aero towing. The glider's manual stated that the stall speed for the glider in level flight is 28 miles per hour (mph). The glider's manual additionally stated that "a pronounced buffeting will occur before the stall" and it "generally falls straight through without a tendency to fall off on a wing." The manual specifies that in a turning maneuver the glider "always falls in the direction of the turn with no tendency to go over the top." The glider's flight manual additionally stated that the recommended stall recovery procedures were to "increase flying speed by easing stick forward until nose falls through horizon and then resume desired airspeed" and that "directional control [is] maintained with rudder." The control stick did not have a boot or other protective device around the area where the stick meets the floor. Friends of the pilot reported that the glider had been assembled about 2 days prior to the accident. METEOROLOGY The tow pilot reported that the wind at the time of the accident was varying between 160 and 180 degrees at 10 mph, with sporadic gusts of about 15 mph. He stated that the wind direction and speed was well within his limits for a normal departure and towing operation. The closest aviation weather reporting station was Luke Air Force Base, Glendale, Arizona, which was 47 nautical miles southeast of the accident site. At 1455, the station reported winds from the south-southwest at 10.4 mph; visibility 20 miles; temperature 35 Celsius; dew point 28 Celsius; altimeter setting of 29.72 inHg. WRECKAGE AND IMPACT INFORMATION The wreckage was located about 450 feet east of runway 17, at Sampley's Airport. The glider came to rest on flat desert terrain on an unused portion of property adjacent to a small hangar-type structure. The debris field was confined to the area immediately surrounding the wreckage. The glider was pointed on a southerly bearing. The wings remained attached although the left wing was partially fractured at the spar/wing root area joining at the fuselage. The right wing sustained aft crush deformation to the leading edge, with the outboard tip compressed inward. The cockpit fuselage was fragmented; the structure forward of the pilot's seat was separated from the remaining fuselage. MEDICAL AND PATHOLOGICAL INFORMATION The Maricopa County Office of the Medical Examiner, Phoenix, Arizona, performed an autopsy of the pilot on May 05, 2006. The autopsy reported the cause of death as "atlanto-occipital subluxation due to deceleration injury due to glider crash." The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, 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. TEST AND RESEARCH Glider Examination An FAA inspector examined the glider at the accident site and several days later after it had been recovered. He stated that he confirmed control continuity of the flight controls from the cockpit to the control surfaces. During the examination he did not see evidence of any anomalies that may have precluded normal operation. Flight Recorder The glider was equipped with a Cambridge Aero Instruments, GPS Secure flight recorder serial number C0YS. It is unknown when the recorder was last calibrated. The unit was sent to the manufacturer to be downloaded. A Safety Board investigator reviewed the tabular data and additionally used a computer program specified by the recorder manufacturer to graphically plot that data from the recorder. A review of the data showed that a data sampling was recorded every 4 seconds. The flight started at 2104:22, which was determined by an increase in ground speed, consistent with a taxi operation. The highest altitude was the last recorded data point at 2,507 feet mean sea level (msl), which corresponded to the glider gaining 210 feet during the flight. The last data point occurred at 2128:56, with a depicted ground speed of about 57 mph; the global positioning system (GPS) coordinates for that point were 33 degrees 55 minutes 44 seconds north latitude and 113 degrees 10 minutes 87 seconds west longitude. The distance from the last recorded position to the accident site was approximately 2,000 feet to the southeast. The last 20 seconds of flight reflected a derived ascent of about 630 feet per minute (fpm) based on pressure altitude recorded and 453 fpm ascent based on GPS. A review was conducted of the flight taken 2 days prior to the accident flight. The takeoff profile of the prior flight (first 20 seconds) revealed a slower altitude gain, reaching 2,365 feet at the last hit.
The pilot's failure to maintain control of the glider during takeoff-initial climb, which resulted in a broken tow rope, a spiral, and an in-flight collision with terrain. A factor associated with the accident is the pilot's failure to correct the spiral.
Source: NTSB Aviation Accident Database
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