Accident at Seattle, Washington, 19 Jul 1949

Accident narrative

On July 19, 1949, an Air Transport Associates C-46F crashed into a residential area following takeoff from Boeing Field in Seattle, Washington. The aircraft struck several dwellings, killing two of the 28 passengers and five people on the ground. Two passengers, the four crew members, and four people on the ground were seriously injured, while 15 passengers received minor injuries.

### The flight

The non-stop flight to Chicago, Illinois, taxied from the loading ramp at 2048. The aircraft was loaded with 8,010 pounds of fuel and 912 pounds of baggage. Its total weight of 44,907 pounds was within the allowable limit of 45,000 pounds, and the center of gravity was within certificated limits.

Captain Merle Edgerton was flying from the left seat. He had 3,743 flying hours, including 700 in C-46 aircraft. First Officer Anthony Gjessing, in the right seat, had 7,800 flight hours but had been employed by the company just three days prior and had received no company flight instruction before this trip. A reserve captain, James M. Adams, was seated on the flight deck behind them.

### The accident sequence

The crew taxied to the south end of runway 31 and parked for 13 minutes to complete the pre-takeoff checklist. At 2058, cleared by the tower, the takeoff roll began. The fuel selector valves were positioned to the front tanks, which contained 91 octane gasoline. The center tanks held 100 octane gasoline, but they were not used because the left center fuel pressure boost pump was inoperative. The weather was clear with a ceiling of 8,500 feet, eight miles of visibility, and a six-mile-per-hour northeast wind.

Power was advanced to 45 inches of manifold pressure and 2,700 RPM. After rolling approximately 3,500 feet, the aircraft became airborne at 105 miles per hour. During the roll, one engine was heard to sputter and backfire, and an unusual amount of exhaust flame was seen coming from both engines. Because the left engine did not seem to be developing full power, Captain Edgerton retarded the throttles at an altitude of about 20 feet, and the aircraft settled back onto the runway.

The aircraft touched down 4,500 feet from the start of the takeoff run. Runway 31 was 7,500 feet long, but the green threshold lights at the north end had been moved in 1,700 feet for repairs. Captain Edgerton touched down 1,300 feet from these lights and did not believe he had sufficient runway remaining to accomplish a safe stop. He advanced the throttles to their limit of 52 inches. Both engines responded, but the left continued to misfire. After a momentary ground roll, the aircraft became airborne again at 105 miles per hour.

With the landing gear retracted, the speed slowly increased to 110 miles per hour. The aircraft passed the north end of the runway at about 50 feet in a nose-high attitude. Unable to gain sufficient altitude to clear power lines and poles north of the airport, the aircraft struck a 56-foot pole 1,500 feet north of the runway, hitting it two feet below its top. The impact tore away six feet of the right horizontal stabilizer and elevator.

The aircraft struck a second pole 1,480 feet further on, and a third pole 200 feet after that. Losing speed and altitude, it crashed 200 feet past the third pole into a three-story frame house, tearing away the top story before plunging into and demolishing a single-story brick dwelling. The aircraft severed high tension lines carrying up to 26,000 volts, causing electrical arcing that started several scattered fires. Fire broke out in the aircraft's fuel tanks immediately after it stopped, but the fuselage had broken open at the nose and tail, allowing the occupants to evacuate before the fire progressed into the cabin.

### What the investigation found

The wreckage was extensively destroyed by fire. The landing gear was found in the "up" position. Flight controls were too badly damaged to determine their pre-impact positions, though Captain Edgerton stated he had taken off with the flaps up.

Investigators noted that the aircraft's specification provided only for the use of fuel of 100 octane rating or above. The company was operating the aircraft in accordance with a manual that allowed 91 octane fuel for cruise, but not for takeoff.

The engines were a war model of the Pratt and Whitney R-2800-75. Because they were obsolete, no manufacturer service bulletins were available, and the company relied on Army Technical Orders for maintenance. Disassembly of the left engine revealed a missing contact spring for the magneto distributor finger, cratered magneto contact points, excessive end movement in a rocker arm bearing, and a wet or oily condition in the combustion chambers. The right engine had a broken outer exhaust valve spring and a lesser oily condition.

Although no physical evidence of detonation was found, the Board noted it was probable during takeoff because the high power settings used far exceeded the limitations of 91 octane fuel. The Board concluded that the use of 91 octane fuel could have caused the engine maloperation and resultant loss of power, though the extent of the power loss could not be determined due to fire damage.

The left engine had also misfired during a takeoff from Annette, Alaska, the day before the accident. Maintenance personnel in Washington had subsequently replaced parts in the left carburetor's mixture control unit, after which the engine operated normally.

The Board noted that the company did not require its previously employed pilots to complete a training program or flight check. When examined, Captain Edgerton could not state the minimum airspeed required for a safe single-engine takeoff. The Board concluded that his indecision stemmed from this lack of knowledge. If he had not retarded the throttles initially, the aircraft would have been at least 20 feet higher and would have cleared the first pole. Conversely, if he had maintained his decision to abandon the takeoff, there remained 3,000 feet of usable runway, which the Board noted should have been ample distance to stop.

### Probable cause

The Board determined that the probable cause of this accident was "the indecision of the pilot in continuing a takeoff after loss of power in the left engine, which loss was probably caused by the use of 91 octane fuel, necessitating the operation of the aircraft's engines in excess of the approved operating limitations."