Accident Overview
A float-equipped airplane, operated by a commercial pilot as a visual flight rules cross-country flight in conjunction with his guiding service, experienced an unintended engine power reduction during cruise. The pilot reported that approximately 20 minutes after departing from one lake en route to another, the engine rpm dropped to idle. He advanced the throttle control and maneuvered the airplane toward a lake, but it descended into trees short of the intended landing area. The airplane sustained extensive damage to the wings and fuselage.
Aircraft Examination
Post-accident examination of the airplane revealed that the support shaft for the throttle and mixture bell cranks was missing. This condition disconnected the throttle control and allowed the engine to remain at idle power. Further examination of the air induction box assembly identified that the air box (part number 1650012-1) had been repaired using incorrectly substituted components. The correct solid shaft bushings had been replaced with earlier generation roller bearings. This inappropriate installation prevented the support shaft from being properly pinned in place and eliminated the redundant safety feature of the original design. The correct installation would have precluded the support shaft from migrating out of the air box if either shaft end spacer were missing.
Maintenance Findings
A review of the airplane's maintenance log books did not reveal any entries pertaining to the air box repair. The pilot stated that there were no known mechanical problems with the airplane prior to the flight.