NTSB Factual Report

HISTORY OF FLIGHT

On July 31, 2001, about 1835 Alaska daylight time, a float-equipped Cessna 172 airplane, N5312T, operated by Beaver Air Taxi as a Part 135 sight-seeing flight, sustained substantial damage following a reported loss of engine power and subsequent collision with terrain. The accident occurred approximately 12 miles east-southeast of Eagle River, Alaska. The commercial pilot/owner of the airplane was not injured, one of the three passengers received serious injuries; the other passengers were not injured. The local flight departed the Lake Hood Seaplane base, Anchorage, Alaska, about 1815, and operated in visual meteorological conditions.

During multiple telephone and in-person conversations between the pilot and the NTSB investigator-in-charge, the pilot related he was conducting a sight-seeing flight in the Eagle River Valley. He said he departed the Lake Hood Seaplane base about 1815, and that the flight was initially uneventful and routine. While passing through 2,200 feet msl in a slight climb, he said the engine began missing, and then to shake and smoke, and rapidly lose power. He looked for an emergency landing site, shut the engine down, and made an emergency landing to a slough and sandbar in the Eagle River. He wrote, in part, in his report to the NTSB: "When it was apparent I was not going to make the intended spot, I reversed engine shut down procedures in an attempt to restart the engine with no results and chose a slough in the river with willows and alders on each side, pulled in the last two notches of flaps and stalled the airplane into the slough which resulted in the wings and floats absorbing the forward energy. The airplane came to rest upside down." The pilot also noted that rescue personnel took him and the passengers to a local hospital, where they were all treated and released. The most serious injury appeared to be one passenger who had two broken ribs.

AIRCRAFT INFORMATION

The airplane, a Cessna 172, had been modified to accept float landing gear and a 220 horsepower, Franklin 6A-350-C2 engine. The engine had been overhauled by Debs Aircraft, Sunny Valley, Oregon, approximately 180 service hours prior to the accident. The overhauled engine was installed in the accident airplane on June 6, 2001.

WRECKAGE AND IMPACT INFORMATION

The airplane came to rest inverted on a sandbar in the Eagle River, surrounded by water. The main landing gear floats, wings, and empennage had extensive crushing and tearing, with the empennage still attached to the remainder of the airframe, but bent approximately 90 degrees to the left, just behind the cabin structure. The cabin itself was relatively undamaged. All major components of the airplane were at the crash site. The wreckage was removed from the sand bar by a helicopter on August 6, and taken to a maintenance/storage facility in Wasilla, Alaska.

The NTSB IIC and two FAA Aviation Safety Inspectors (airworthiness) examined the airplane at the maintenance facility on August 15. The engine was removed and partially disassembled. Disassembly disclosed numerous fragments and chunks of metal in the engine oil pan, and that the number five piston had disintegrated. The number five piston connecting rod, and approximately 3/4 of the wrist pin, were still remaining; approximately 1/4 of the wrist pin had fractured and was not located. The remainder of the engine was unremarkable. The number five cylinder wrist pin was still partially seated in the connecting rod, and that connecting rod, wrist pin, and wrist pin bushings, were sent to the NTSB's Material Laboratory in Washington, DC, for analysis. Also sent as exemplars were a wrist pin, wrist pin bushings, and piston from the number six cylinder. The materials engineer's report regarding the examination of the components is attached.

TESTS AND RESEARCH

The materials engineer's report disclosed that the number five wrist pin had fracture characteristics consistent with multiple fatigue sites. The wrist pin met factory specified dimensions, but was slightly below the specified case hardness. The number five wrist pin bushings were not marked as noted by factory engineering specifications, and were slightly undersized. See the engineer's attached report for specifications and photographs.

The NTSB did not take custody of the wreckage, other than the components sent to the NTSB's materials laboratory. Those components were returned to the airplane's owner via registered mail on March 6, 2002.

NTSB Probable Cause

The fatigue induced fracture of a connecting rod wrist pin, resulting in a complete loss of engine power.