Narrative:

In cruise at 6500 MSL the temperature sixty degrees fahrenheit. Approximately fifteen minutes after departure after opening flight plan and requesting flight following the engine began to shudder lightly and power was reduced. Fuel flow dropped from eight to nine gph to below two gph registered on fuel flow gauge. Pilot applied full throttle; prop; and mixture and was unable to maintain altitude. Pilot immediately notified ATC of the issue and began immediate diversion to nearest airport. ATC asked if assistance was needed. Pilot declined as the engine appeared to just be running rough but was producing some power. Pilot executed additional troubleshooting by applying electric fuel boost on current tank with no effect. Pilot turned off boost; switched tanks with no change. Pilot again applied fuel boost with no change. ATC advised pilot to switch to unicom airport was in sight. While in decent pilot moved throttle rearward and engine sounded as though it would cut off if reduced further. Pilot applied full throttle again to keep engine running. While in the decent on an elevated base leg at 1500 MSL with landing gear extended and full flaps engine power returned and pilot landed safely. Once on the ground pilot conducted a run-up check with no issues noted. Pilot shut aircraft down conducted another full inspection of aircraft to include looking at the air filter for signs of induction icing. Carburetor ice was not an issue as plane is fuel injected. Pilot completed checklist again and sumped the tanks and engine with no signs of water. Pilot conducted another run-up test; twice conducted full power test as an extended taxi; and completed another run-up test. No issues were noted from all tests and pilot deemed aircraft airworthy. Pilot departed; climbed to an altitude allowing glide distance to airports along the way; landed at airport of intended destination and had plane inspected by a mechanic for the described problem that occurred in flight. Mechanic located source of problem. It was the alternate engine air source flutter/door had broken off at the hinge and covered the engine air source by 2/3rds thus reducing the engine ability to generate full power and causing a noticeable reduction in fuel flow. During decent it is assumed the door fell from the position of blocking air intake and remained in that position through all the ground checks and continued flight to destination. The plane was repaired and returned to service. The pilot took all precautions that would have been visible to the average to above average pilot. However; the significance of hidden danger of the alternate door failing and becoming lodged again could have caused an in flight emergency during take-off or cruise.

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Original NASA ASRS Text

Title: A BE24 pilot reported power loss at 6500 feet and diversion to nearby airport. During approach engine returns to normal operation. Post flight inspection can find no cause and high power run ups are normal. The pilot continued to destination where a mechanic found the alternate air source door broken hinge to be the cause.

Narrative: In cruise at 6500 MSL the temperature sixty degrees Fahrenheit. Approximately fifteen minutes after departure after opening flight plan and requesting flight following the engine began to shudder lightly and power was reduced. Fuel flow dropped from eight to nine GPH to below two GPH registered on fuel flow gauge. Pilot applied full throttle; prop; and mixture and was unable to maintain altitude. Pilot immediately notified ATC of the issue and began immediate diversion to nearest airport. ATC asked if assistance was needed. Pilot declined as the engine appeared to just be running rough but was producing some power. Pilot executed additional troubleshooting by applying electric fuel boost on current tank with no effect. Pilot turned off boost; switched tanks with no change. Pilot again applied fuel boost with no change. ATC advised pilot to switch to UNICOM airport was in sight. While in decent pilot moved throttle rearward and engine sounded as though it would cut off if reduced further. Pilot applied full throttle again to keep engine running. While in the decent on an elevated base leg at 1500 MSL with landing gear extended and full flaps engine power returned and pilot landed safely. Once on the ground pilot conducted a run-up check with no issues noted. Pilot shut aircraft down conducted another full inspection of aircraft to include looking at the air filter for signs of induction icing. Carburetor ice was not an issue as plane is fuel injected. Pilot completed checklist again and sumped the tanks and engine with no signs of water. Pilot conducted another run-up test; twice conducted full power test as an extended taxi; and completed another run-up test. No issues were noted from all tests and pilot deemed aircraft airworthy. Pilot departed; climbed to an altitude allowing glide distance to airports along the way; landed at airport of intended destination and had plane inspected by a mechanic for the described problem that occurred in flight. Mechanic located source of problem. It was the alternate engine air source flutter/door had broken off at the hinge and covered the engine air source by 2/3rds thus reducing the engine ability to generate full power and causing a noticeable reduction in fuel flow. During decent it is assumed the door fell from the position of blocking air intake and remained in that position through all the ground checks and continued flight to destination. The plane was repaired and returned to service. The pilot took all precautions that would have been visible to the average to above average pilot. However; the significance of hidden danger of the alternate door failing and becoming lodged again could have caused an in flight emergency during take-off or cruise.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.