EPHRATA, WA, USA
N3189Z
Piper PA-18-150
During a glider tow, the glider pilot failed to ensure that his aircraft's spoilers were retracted in the locked position during takeoff. During the initial climb, the towplane pilot radioed 'SPOILERS, BOB, SPOILERS' and a witness observed seeing the spoilers extended. The glider pilot retracted the spoilers during which the glider entered a nose-high, pitch up attitude. Realizing he was in a high tow position, and before he was able to manually release the tow line from the glider, the tow rope broke in overload and within the specified tensile limits per regulatory requirements. A witness observed seeing the towplane climb to approximately 150 feet AGL and then pitch nose down, descending in an approximate 45 degree flight path to a wings level ground impact. The aircraft impacted the terrain 40-50 degrees nose low, wings-level with the engine developing power. Examination of the aircraft's tow hook release latch mechanism revealed the potential for binding of the release latch when the towed aircraft moved significantly above the horizontal (trail) position.
HISTORY OF FLIGHT On June 3, 1999, approximately 1441 hours Pacific daylight time, a Piper, PA-18-150, N3189Z, registered to Puget Sound Soaring Association, and being flown by a commercial pilot, was destroyed during a collision with terrain at the Ephrata Municipal airport, Ephrata, Washington. The pilot was fatally injured and a post crash fire consumed the aircraft. Visual meteorological conditions existed, and no flight plan had been filed. The flight, which was engaged in a glider tow operation, was to have been operated under 14CFR91, and originated from the airport immediately before the accident. The glider pilot reported in a written statement that "after the towrope was taut the glider pilot radioed the towplane to takeoff. The takeoff was started and the glider was airborne at about 35 knots. The towplane was also noted to be airborne at this time. A second or two later the towpilot advised on the radio 'SPOILERS, BOB, SPOILERS.' The glider pilot saw his spoilers up about two inches, grabbed the spoiler handle, pushed forward and locked the spoilers. He then saw he was in a nose high, pitch-up position. He pushed forward on the stick, then realizing he was in a high tow position, he reached for the release knob but the rope broke before he could reach it" (refer to attached NTSB Form 6120.1/2). The glider pilot observed that the tow plane had crashed and executed a 180 turn returning and landing at the airport. The glider pilot was interviewed and reported observing the Piper's flaps extending during the takeoff/climb phase. An ear witness located at the south end of the airport ramp reported hearing the engine of the Piper at full power throughout the takeoff and continuing to the time of impact. He also reported that he heard no coughing or sputtering and that the engine's performance sounded smooth and consistent. An eye witness located near the glider launch area reported observing the two aircraft take off and climb to approximately 150 feet above ground. The witness also reported seeing the glider's spoilers extended and observed the glider pitch up. He further reported that shortly thereafter, the tow plane pitched nose down and descended in an approximated 45 degree descending flight path, wings level, to ground impact. PERSONNEL INFORMATION Information provided by relatives indicated that the pilot of the Piper was reported to have had 4,316 total flight hours. He was also reported to have had 349 total flight hours in the accident aircraft make/model (11 within the previous 90 days to the accident), and 109 total flight hours in glider aircraft. The glider pilot reported that he had logged a total of 11,800 flight hours. He also reported that he had logged 162 hours of glider flight time, of which 33 hours were in the Schempp-Hirth Standard Cirrus glider. He also reported no flight time in the glider within the previous 90 days to the accident. AIRCRAFT INFORMATION The Piper PA-18-150, serial number 18-7182, was equipped with a Textron Lycoming O-320-A2B, 150 horsepower engine. Total aircraft time as of 01/04/99, was logged as 5,886.9 hours. The number of additional flight hours accrued between that date and the date of the accident was unknown. The engine was overhauled and zero-timed by Textron Lycoming on 04/25/92, and installed in the airframe 07/03/92, at an airframe time of 4,909 hours. The Piper was equipped with a tow rope release mechanism located at the aft of the empennage and above the tailwheel. The tow rope's forward attach ring was normally looped over the rotating "J" hook at the aft of the mechanism. The "J" hook was free to rotate about its end through a bolt. When the "J" hook was rotated into the CLOSED position, the forward end of the hook (oriented forward) rested against a pin which joined the two halves of the release bracket. The release bracket, like the "J" hook, was free to rotate about its end through a bolt. The opposite end of the bracket could be pulled forward by means of a cable attached at its end and routed to the cockpit, thus releasing the forward end of the "J" hook (refer to photograph 1). When the pilot pulled the tow release cable, the bracket would rotate forward slipping off the forward end of the "J" hook. This action would allow aft tension from the tow rope to rotate the "J" hook to an OPEN position thus releasing the tow rope. Under normal conditions of physics, when the tow rope/glider is positioned relatively horizontal to the tow plane release mechanism, the tensile forces on the release mechanism are oriented aft (refer to photograph 2). However, should the tow rope/glider move into a position significantly above the horizontal, the tensile forces on the release mechanism would resolve into an aft vector and an up vector. As the upward vector increases the force applied by the "J" hook against the pin which joined the two halves of the release bracket would likewise, increase (refer to photograph 3). The Piper PA-18-150 owner's manual provided performance data for the aircraft (refer to ATTACHMENT OM-I). The best angle of climb (ratio) at sea level under standard conditions was reported as five to one. The Schempp-Hirth Standard Cirrus glider (N71LS) was a single-place glider with a maximum weight of 800 pounds. It was equipped with spoilers on each wing. The spoilers were flat plates, mounted vertically within the wing and extended by means of a push/pull tube actuator located within the cockpit and to the left of the pilot's seat. When the push/pull tube actuator was pulled aft, the spoilers extended vertically out of the top surface of each wing, dumping lift and creating parasitic drag. Each spoiler plate was equipped with a top cap slightly larger in size than the top of the spoiler profile, such that a small lip extended around the top of the spoiler, creating a "T" profile when viewed along each wing's lateral axis. This lip lay flush with the upper surface of the wing when the spoilers were retracted, but would create a small air dam at the top of each spoiler when extended. An over-center lock existed within the spoiler extension mechanism which would engage when the spoiler extension push/pull tube actuator was pushed fully forward (parallel to the glider's longitudinal axis). The over-center engaged within the last approximate inch of forward travel of the push/pull tube actuator and, when fully engaged, the two hexagonal nuts at the forward end of the push/pull tube actuator would rest against one another (refer to photographs 4 and 5). A rotating handle or "pistol-grip" was attached to the forward end of the push/pull tube actuator. The grip was free to rotate from its normal six o'clock position to the three o'clock position, which would facilitate easier extension of the spoilers. It was noted that when a pilot of the glider applied forward pressure to retract and lock the spoilers in the down position while maintaining his right hand on the glider's control stick, it was possible to induce an inadvertent aft stick or pitch-up condition. It was also noted that with the spoiler push/pull tube actuator extended fully forward to the over-center point, BUT NOT beyond and into the locked detent, the spoilers appeared visually flush and fully retracted with the top of each wing. The glider pilot commented under "Recommendation (How Could This Accident Have Been prevented)" (refer to NTSB Form 6120.1/2) that: "A more thorough and responsive checklist. Should read - SPOILERS - CHECKED and LOCKED rather than "SPOILERS." A tape or painted marker on [the] inside of [the] cockpit to indicate when [the] spoiler handle is in [the] locked position." METEOROLOGICAL INFORMATION The aviation surface weather observation taken at 1452 hours at the Ephrata Municipal airport reported the winds at 5 knots from 050 degrees magnetic with no gusts reported. The temperature was reported as 84 degrees Fahrenheit. AERODROME INFORMATION Glider operations at the Ephrata Municipal airport (airport elevation 1,272 feet above mean sea level) were being conducted from the asphalt surfaced ramp area paralleling runway 02/20 at the time of the accident. The rectangular ramp area measured approximately 500 feet wide and 3,500 feet in length and tow planes/gliders were launching parallel to runway 20 at the time. The glider was positioned near glider spot "25" on the ramp with the tow plane positioned approximately 150 feet southwest (with the tow rope fully extended). Spot "25" measured approximately 1,290 feet and 024 degrees magnetic from the ground impact site of the Piper (refer to photograph 6 and DIAGRAM I). WRECKAGE AND IMPACT INFORMATION The aircraft crashed just beyond the southwest edge of the Ephrata Municipal airport ramp, Ephrata, Washington. The accident site coordinates were determined using a handheld GPS unit and were found to be 47 degrees 18.412 minutes north latitude and 119 degrees 31.487 minutes west longitude. The elevation of the accident site was approximately 1,260 feet MSL (refer to DIAGRAM I). The terrain at the initial ground impact site was level and consisted of hard packed soil and mixed rock fragments. All components of the aircraft were found at the aircraft's final resting place and the aircraft had been consumed by a post-crash fire (refer to photographs 7 through 10). The first evidence of ground impact was a crater in the soil approximately 3 inches deep. The aircraft (engine) came to rest at a point bearing 204 degrees magnetic from the initial ground impact site and approximately 19 feet beyond. The majority (143 feet) of the 156 foot long tow rope was observed lying on the ground in a roughly coiled heap slightly north-northeast of the aircraft's tow release hook (refer to photograph 11). The aircraft was observed to have come to rest at a point bearing approximately 204 degrees magnetic and 1,150 feet from the point where it began it's initial takeoff roll (refer to photograph 12). Both wings remained attached to the fuselage and the approximate bearing line measured along the lateral axis through the wings at the final resting place was 314/134 degrees magnetic. Both wings displayed symmetrical leading edge impact deformation which was observed to become more pronounced towards the outboard section of each wing (refer to photographs 13 and 14). Fragments of green glass, characteristic with the color and size of the right wingtip navigation lens, were observed lying on the ground slightly northwest of the initial ground impact crater. Likewise, fragments of red glass, characteristic with the color and size of the left wingtip navigation lens, were observed lying on the ground slightly southwest of the initial ground impact crater. The magnetic bearing line between these two areas of broken glass passed through the initial ground impact crater and was parallel to the previously described 314/134 degree bearing line (refer to page 3, Supplement I). The horizontal and vertical stabilizers as well as their respective control surfaces remained attached to the empennage. The empennage was observed to be displaced slightly counter-clockwise from the longitudinal axis of the aircraft when viewed from above (refer to photographs 15 and 16, and page 3, Supplement I). The elevator trim tab jackscrew was observed in a near neutral position. The tow rope was observed to have been melted through approximately one foot aft of the attach ring which engaged the tow release hook. The hook and short section of rope was located almost directly beneath the tow hook release latch at the site. The propeller spinner was observed to be substantially deformed in an aftward direction. The fixed pitch propeller displayed minimal bending deformation on one blade and extensive lateral and chordwise scratching and aftward bending on the opposing blade (refer to photographs 17 and 18). The aircraft was raised above the terrain using a winch and a side view of the engine was photographically captured. The angle between the engine's longitudinal axis and the crush line on the underside of the engine was measured to be approximately 40 degrees (refer to photograph 19). Control continuity was established from each control surface, the engine throttle and mixture control into the cockpit area. MEDICAL AND PATHOLOGICAL INFORMATION Post-mortem examination of the pilot was conducted by Gerald Rappe, M.D., at the facilities of Central Washington Hospital, Wenatchee, Washington, on June 4, 1999, (case number 99-0603-099). Toxicological evaluation of samples from the pilot was conducted by the Federal Aviation Administration's Toxicology Accident and Research Laboratory, Oklahoma City, Oklahoma. The findings were reported as follows: ATTENOLOL detected in blood ATTENOLOL detected in urine SILDENAFIL detected in blood DESMETHYLSILDENAFIL detected in blood SILDENAFIL detected in urine DESMETHYLSILDENAFIL detected in urine All other findings were negative (refer to the attached toxicology report) TESTS AND RESEARCH The tow rope was submitted to the NTSB Materials Research laboratory in Washington, DC, for further examination. The rope was subjected to several tensile failure tests with the failure occurring at 867 and 953 pounds. Federal Air Regulations 14 CFR 91.309 Towing: Gliders states in part that: (a) No person may operate a civil aircraft towing a glider unless-- (3) 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. The failure criteria of these tests satisfied the standard set forth in 14CFR91.309(a)(3) (refer to attached Materials Laboratory Factual Report). ADDITIONAL INFORMATION On-site examination of the wreckage was conducted on June 4, 1999, after which the wreckage was verbally released to Ephrata Municipal airport authorities until arrival of the insurance representative. Written wreckage release was accomplished on June 7, 1999, and is documented on NTSB form 6120.15 (enclosed).
The glider pilot's failure to maintain control of his aircraft during spoiler retraction, which led to the Piper pilot's inability to recover safe flying airspeed within the altitude constraints at the time of the event. Contributing factors were the failure of the glider pilot to ensure that the spoilers were locked prior to takeoff, and the binding of the tow aircraft's tow hook release latch.
Source: NTSB Aviation Accident Database
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