ANC13LA079

The private pilot reported that she was on a cross-country flight in a float-equipped airplane, and that, about 20 minutes into the flight, the engine rpm suddenly dropped to idle. She moved the throttle forward, and the engine momentarily responded, but it again dropped to idle power. She switched fuel tanks, but the engine still did not respond, so she initiated a forced landing to brush-covered tundra. During the forced landing, the airplane nosed over, which caused substantial damage to the wings, fuselage, and empennage. Examination of the engine revealed that the clamp that secures the throttle cable was loose, which allowed the throttle cable housing to move inside the clamp. The engine was started without tightening the throttle cable clamp, and it operated normally through various power settings. Given the loose throttle cable clamp and the pilot's account of the accident sequence, it is likely that the throttle cable housing was free to move when the throttle lever moved, which limited the amount of throttle authority available to the pilot.

On August 13, 2013, about 1240 Alaska daylight time, a float-equipped Piper PA-18-150 airplane, N44RT, sustained substantial damage during a forced landing following a partial loss of engine power near Paxson, Alaska. The private pilot and one passenger were not injured. The airplane was registered to, and operated by the pilot as a visual flight rules personal cross-country flight under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Tangle Lakes, Alaska about 1220, destined to Anchorage, Alaska. In a written statement to the National Transportation Safety Board (NTSB), the pilot said that approximately 20 minutes into the flight, the engine suddenly went to idle RPM. She moved the throttle forward and received a momentary response, but the engine again went to idle power. She switched fuel tanks, and the engine still did not respond, so she initiated a forced landing in an area of brush covered tundra. During the forced landing, the airplane nosed over, sustaining substantial damage to the wings, fuselage, and empennage. The closest official weather observation station is located at the Gulkana Airport, Gulkana, Alaska, about 52 miles south of the accident site. At 1253, an Aviation Routine Weather Report (METAR) was reporting, in part: Wind, 160 degrees (true) at 6 knots; visibility, 10 statute miles; clouds and sky condition, clear; temperature, 72 degrees F; dew point, 48 degrees F; altimeter, 29.95 inHg. On August 20, the NTSB investigator-in-charge, along with an inspector from the Anchorage Flight Standards District Office, examined the airplane at the facilities of Alaska Claims Services, Inc., Wasilla, Alaska. The examination revealed no preaccident anomalies with the airframe that would have precluded normal operation. Examination of the Lycoming O-320-B2B engine revealed that the throttle cable clamp was loose around the throttle cable, allowing the cable housing to move as well as the cable to move inside the housing. The airplane was secured and the engine was started and run for approximately 10 minutes through various power settings without anomaly. The airplane underwent an annual inspection on June 27, 2013, and had flown approximately 10 hours since being returned to service. The throttle cable clamp that was used to secure the throttle cable in the airplane is known in the community to loosen and allow the cable to slip. While there is no requirement to do so, many Piper PA-18 operators and mechanics use safety wire on both sides of the clamp to ensure security of the cable. The clamp on the accident airplane was not secured with safety wire.