LAX94FA354

Immediately after the airplane took off, witnesses heard an abnormal sound from the engine, and then the engine sound stopped momentarily and resumed. The aircraft entered a right 180-degree turn. While in the turn, another power interruption occurred before the engine stopped completely. Ground witnesses said that after the final engine stoppage, the aircraft stalled and spun into the shoreline. High tide caused the airplane to shift before it was inspected. The fuel primer control was found unlocked and extended. The fuel selector was found positioned to the right tank. Although both main fuel tanks had ruptured on impact, there was significantly more fire damage and hydraulic deformation associated with the right main tank than the left. A computation of fuel consumption indicated that about 23 gallons of fuel had been used since the airplane was last refueled. The capacity of each tank was 23 gallons of usable fuel. No preimpact mechanical failure was found.

History of flight

On September 5, 1994, at 1246 Pacific daylight time, a Stinson 108-3, N6446M, was destroyed by impact and postcrash ground fire during an attempted forced landing at Shelter Cove, California. The aircraft was owned and operated by the pilot and was on a cross-country flight to Lodi, California. Visual meteorological conditions prevailed at the time and no flight plan had been filed for the operation. The certificated private pilot and his three passengers sustained fatal injuries. The flight was originating at the time of the accident.

According to family members, the pilot had been on a 3-day vacation in Shelter Cove. The aircraft arrived on September 2, 1994, and was making a midday departure on a return flight to Lodi, California. The estimated flying time on the flight from Lodi was approximately 1 hour 45 minutes. The flying time on the return flight was estimated to be the same duration. The Shelter Cove airport is unattended and provides no fueling services.

Witnesses reported seeing the aircraft taking off from runway 12. One witness described the aircraft's initial climb as a "maximum performance takeoff," stating that the climb angle appeared steeper than normal. As the aircraft reached the end of the runway, several witnesses described hearing a "popping" sound from the engine. The witnesses then stated that the engine sound stopped momentarily, but then resumed almost immediately. The witnesses also reported that the nose of the aircraft momentarily pitched downward in unison with the abrupt engine stoppage and then pitched up again as the engine sounds resumed.

After reaching the field boundary, witnesses described the aircraft as entering a 30- to 45-degree banked right turn, which continued for approximately 180 degrees. Witnesses said that while in the turn the engine again "popped" and stopped momentarily, resumed operating, and then stopped abruptly. One witness stated that after the engine stopped for the final time, the aircraft appeared to stall and entered a spin to the right. The witness said that he watched the aircraft spin about 1 1/2 revolutions before it impacted in a near vertical nose-down attitude on a rock formation along the Pacific shoreline.

Personnel information

According to a Federal Aviation Administration (FAA) inspector, and based on a review of the pilot's logbook, the pilot held an expired third-class medical certificate and had not completed a biennial flight review.

The pilot had reported a total of 700 flight hours total time at the issuance of his last medical certificate in 1991. He had been a licensed pilot since 1966. In addition, the pilot, who was also a licensed airframe and powerplant mechanic, reportedly performed all the maintenance tasks on the aircraft.

Aircraft information

The aircraft was modified with the installation of a Franklin 6AS-335-A engine and Garrett turbo charger system. The engine is capable of producing 260 horsepower.

A representative of another engine manufacturer, who was acquainted with the pilot and familiar with the aircraft, estimated the normal cruise airspeed at 60 percent power to be approximately 113 knots with a fuel consumption of approximately 12.5 gph. A flight from Lodi to Shelter Cove under no wind conditions would consume nearly 19 gallons plus .75 gallon for start, taxi, and run-up. The additional fuel used in the initial climb to altitude was estimated to have increased overall fuel consumption by 3 gallons when using a 70 percent power setting.

According to FAA records for the accident aircraft, the total fuel capacity was 50 gallons, 25 gallons in each main wing tank. There were 4 gallons of unusable fuel, 2 gallons in each tank. According to the pilot's logbook, the aircraft was last flown on August 21, 1994, when it returned to Lodi from Pine Mountain Lake. Fuel records of the refueler at Lodi airport show that the pilot purchased 17.448 gallons of fuel at 1642 on September 2, 1994.

Investigators estimated that the weight and balance of the aircraft were within prescribed limits.

According to aircraft logbook entries, the aircraft had completed an annual inspection on June 3, 1994. A review of available maintenance records did not reveal any discrepancies.

Airport information

The runway at Shelter Cove airport is posted right traffic for runway 12. Right traffic positions an aircraft over the coastline upon completion of the crosswind leg. There are several houses between the downwind leg and the runway with several more in that area under construction. The terrain at the coastline drops vertically to the shoreline.

Wreckage and impact information

The final heading of the aircraft after the initial impact was 090 degrees, approximately 1,200 feet southwest of the runway. The aircraft came to rest on a rock formation that protruded from the water at the shoreline. Portions of the aircraft were submerged or partially submerged in several tidal basins located immediately surrounding the main rock outcropping. High tide occurred prior to inspection and recovery of the aircraft resulted in the aircraft being washed and shifted about by waves breaking over the wreckage.

A postaccident inspection of the aircraft revealed that the fuel primer control was unlocked and extended. There were no impact signatures on the primer control handle. The fuel selector was on the right tank and there were no detectable blockages or obstructions in the fuel lines. Although both main fuel tanks had ruptured on impact, there was significantly more fire damage associated with the right main tank than the left. The right tank also exhibited evidence of hydraulic deformation. The gascolator was burned and separated. The carburetor had been crushed, separated, and burned. Neither the gascolator nor the carburetor contained any residual fuel. There was no residual fuel in either main tank.

Flight control continuity was established to the ailerons, elevator, and rudder. The flaps are mechanically actuated and were burned away. The final flap position was not established. The elevator trim was also mechanically actuated. The trim tab was found in the tab up position; however, the tab position was not fixed and moved easily with direct pressure on the tab surface. The final trim position was not established.

The aircraft was equipped with a Hartzell variable speed, constant speed propeller. Both blades had evidence of chordwise gouges; however, there was no evidence of leading or trailing edge damage on either blade. The tip of one blade was missing at a point about 4 inches inboard from the tip. The engine crankshaft was bent about 30 degrees between the propeller hub and the engine case.

The engine data plate identified the engine as a Franklin model 6AS-335-A, serial No. 60001-2, developing 260 hp on 100 octane aviation fuel. An engine logbook entry stated that the engine had been derated to 200 hp continuous operation and 230 hp for 1 minute at 2,800 rpm and 42 inches of manifold pressure. The engine was equipped with a Garrett turbocharger, model 6AS335A, serial No. 6001-2.

Prior to engine disassembly, continuity was established for all moving components between the propeller and the accessory gear section. Movement was restricted due to impact damage. Less than 1 pint of residual oil remained in the crankcase.

Externally, the push rods and tubes exhibited evidence of impact damage. Upon removal, all the cylinders (1 through 6) did not exhibit any unusual wear patterns. All cylinder liners were in place and secured with liner locks. The cylinder walls did not exhibit any unusual wear patterns. The pistons appeared properly assembled with all oil seal rings in place, appropriately spaced and unbroken. No evidence of detonation was noted on any of the piston heads. All piston pins were easily removed and did not exhibit unusual wear patter