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On August 19, 1993, at approximately 1522 Alaska daylight time, a float equipped de Havilland DHC3 Otter, N321KA, operated by Ketchum Air Service of Anchorage, Alaska, experienced a non- mechanical loss of engine power during climb from Nikabuna Lake, near Iliamna, Alaska. The commercial pilot executed a forced landing on a small pond, and the airplane overran the water area into woodland and caught fire. The airplane was destroyed. The pilot and two passengers were uninjured, while three passengers received minor injuries. The flight had originated in Anchorage at approximately 0800 on a company VFR flight plan with multiple stops on a 14 CFR Part 135 on-demand flight to transport passengers and cargo between lakes and to Anchorage. Visual meteorological conditions existed.
The pilot told investigators that he had 100 gallons of fuel on board, 85 gallons in the centre tank and 15 gallons in the forward tank. Recalling that the engine lost power as he leveled into cruise flight below 1000 feet, above ground level (agl), he said that he "switched tanks to the forward tank and hit the boost pump when it quit, but (the engine) didn't start." The pilot then glided the airplane to a small tundra pond and attempted an emergency landing. The available water landing area was approximately 750 feet in length and the airplane overran the water and entered a wooded area, coming to rest approximately 350 feet from the water's edge.
A passenger, a U.S.A.F. mechanic in the right seat of the airplane, provided a statement that said the "fuel gauges read E" at the time of takeoff from Nickabuna Lake, approximately three minutes before power was lost. That passenger confirmed that the pilot attempted to restart the airplane by use of the electrical boost pump and the starter, but stated that he did not observe the pilot switch fuel tanks.
Witnesses told investigators that a "fire with red flames and black smoke, about 10 feet high lasted about a minute and then turned to white smoke and burned the plane. (See photographs taken by witness.)
INJURIES TO PERSONS
Three of the five passengers reported minor injuries sustained in the impact with the terrain following the forced landing on the small lake.
DAMAGE TO AIRCRAFT
The aircraft fuselage was destroyed from the rear of the engine at the accessory section through the cockpit and cabin to the tail cone by being reduced to ashes by fire. While the accessories mounted on the rear of the engine, as well as the rear of the engine case itself, sustained substantial thermal damage, the front of the cylinders and the propeller was unremarkable. The tail cone and wings, while burned off at their respective junctions with the fuselage, were themselves undamaged. There was no evidence of hydrocarbon soot underneath the horizontal tail surfaces or wing surfaces.
Molten metal and thermal damage to aircraft frame structure was centered at the location of the 40 quart oil tank behind the pilot's seat. (Refer to Wreckage and Impact Information for details of damage to the aircraft.)
The operator advised the investigators that the airplane had undergone a 100 hour inspection on August 9, 1993. An investigation of company records failed to locate certain inspection records for the 100 hour inspection, including the oil sample analysis sheet, or the engine cylinder compression sheet.
The company maintenance director told investigators that an oil sample was drawn and sent for analysis and an engine cylinder compression check was completed at that time. Mr. Craig Ketchum, a company owner, told investigators that an oil sample had been sent to Skywatch Oil Analysis Company following the 100 hour inspection of the engine. The president of Skywatch Oil Analysis Company was contacted and he told investigators that his company had not received an oil sample from the Ketchum company on or after August 9, 1993, nor did the Skywatch company have record of any other recent oil sample drawn from the accident airplane.
Investigators, in reviewing maintenance records for the accident airplane, found that six Airworthiness Directives (AD's) had not been completed on the accident airplane. These AD's required that inspections be performed since 1992 on airplane flight controls, propeller blades, engine cylinders and flight surface integrity.
Witnesses indicated that visual meteorological conditions prevailed at the time of the accident. Photographs of the accident scene, taken by a pilot from the same operator, showed low stratus clouds of an undetermined height, and visibility of three to six miles.
WRECKAGE AND IMPACT INFORMATION
Investigators measured parallel ground scars from west to east, beginning at the edge of a shallow lake, approximately 400 yards in diameter. The scars ended at the wreckage approximately 170 yards from the lake edge. Sixty feet from the wreckage, a rock outcropping found in the left continuous ground scar, was marked and scarred with paint and particles matching those on the left float.
The engine's carburetor had been exposed to thermal energy and was removed for examination.
The propeller was found without visible indication of rotation at impact. One blade of the three-bladed propeller had been thrust vertically into the tundra and the engine, which had been burned away at the firewall mountings, rested on that propeller blade. There was no evidence that the blade had been rotating when it penetrated the tundra. When that blade was withdrawn from the soil and vegetation, there were no scratches of a rotational origin.
The airplane's wings were intact except for a leading edge strike of approximately 6 inches in diameter, on the left wing near the tip. Both wings were drooped as they were burned off at the roots, however they remained aligned at right angles to the fuselage. Neither wing showed evidence of soot on the underside, nor was any scorching found. No soot was found under the horizontal stabilizers of the burned-off tail cone.
The right float showed no impact damage, however showed thermal damage to the inboard face. The right float showed impact damage to the front, misalignment to the diagonal and nearly total thermal destruction under the fuselage.
WITNESS INTERVIEW INFORMATION
The pilot stated, that prior to takeoff from Nikabuna Lake and total power loss shortly thereafter, he observed approximately 100 gallons of fuel indicated on the aircraft's fuel gauge indicator. He said that it was distributed roughly 85 gallons in the centre tank and 15 gallons in the forward tank.
See statements of witnesses attached.
No evidence of fuel or oil residue was found along the ground scar track, before or after the impact mark on the rock outcropping. No fire pattern, burned material or charring was found along the track. No fuel residue was found near or around, in any direction, of the aircraft hull. Scorching of bushes was found adjacent the left fuselage from the firewall location aft to the trailing edge of the left wing, out to approximately two feet.
Scorching of bushes and small trees was similar of the right side of the aircraft to a distance limited by the right float, which sustained thermal damage to its skin on the inboard side. The outboard skin of the right float was unremarkable. No flame pattern or scotching was visible beyond three feet in any direction.
Investigators found the left float diagonally under the fuselage and that float's mounting struts to be impaled into the fuselage underbelly. At the location of that impingement, centered at the location of the center under-belly and lube oil tank, a concentration thermal damage was found to have melted aircraft framework structure.
Investigators found the fuel tank selector switch in the debris of the cockpit. The selector switch was within the arc selected for main fuel tank.
Thermal damage was greatest at the location of the oil tank and continued fore and aft with less thermal damage evident to the remaining cabin structure. The indicator of the degree of thermal damage was the extent to which the fusing and melting of metals had taken place. At the location of the oil tank, thermal twisting and bending of steel cross members, four inches in width had taken place and all aluminum had puddled. At the sides and aft of the cabin, aluminum had been burned but not puddled, and steel parts and cargo was not distorted.
Investigators found that the fire had consumed the aircraft interior and halted at a point before the tail cone, and before burning the wings. The fire had consumed the cockpit instruments and had exposed the rear of the engine to thermal energy sufficient to melt aluminum, where accessory driven units were mounted.
The flora along side the aircraft was a combination of low-bush blue berries and 10 foot to 20 foot black spruce tree. This vegetation showed no thermal damage beyond 24 inches from the burned fuselage. Blueberries at 24 inches from the hull had not been burned.
TESTS AND RESEARCH
The engine driven fuel pump drive shaft was found in the teardown to have sheared. The pump and shaft was sent to the Transportation Safety Board of Canada, for further metallurgical examination and analysis. The findings of that analysis indicate that failure was consistent with failure of the shaft due to seizure from rotation without fuel being present. (See attached report of that examination.)
Investigators found that the operator had no records available to determine when the aircraft departed the remote locations or arrived at the next location. No fueling records were kept at the facility and no records were available to reconstruct the pilot's intended route of flight or names or numbers of passengers on board. No communications were maintained with the pilots operating in the remote areas. Flight following was limited to the arrival or non-arrival of the flight at the end of the day, however, no record of passengers was kept by the operator, except after the fact. Operations records of departures, pilot assignments and passenger names obtained by the investigators were in the form of a spreadsheet filled in by pencil with approximately 30% of the boxes erased or erased and rewritten. The company could not provide a record of the names of the passengers on board the accident airplane until the passengers were returned by Search and Rescue (SAR) aircraft.
The management of the company told investigators while receipts for passenger fares were made out, that the company "threw them away" the same day. Company management could not provide investigators with the fare records or "trip tickets" for the passengers of the accident flight, or any other passengers on the day of the accident, or the following day.
The Pratt & Whitney engine , R-1340-61, SN ZP103122, was examined and torn down at SeaAirmotive, Lake Hood, Anchorage, on August 26, 1993. The procedures and the findings of fact associated with that teardown is attached. (See report attached of FAA Airworthiness Inspector Ernest A. Keener, FSDO-03, party to the NTSB investigation).
All aircraft parts were released to Neil Webster, Professional Adjusters, Anchorage, as agent for the owner/operator.