SEA99FA080

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 8