Narrative:

While I was parking I noticed that the aircraft was on the ramp being worked on. I walked out and asked the mechanic if everything was ok and he told me that everything was good and that he would be finished with the new spark plugs shortly. They finished working on the aircraft and ran the engine up. Everything sounded fine to me from where I was standing. I talked to the mechanic about the airplane. He told me that they had changed the oil and when they ran it up it had been running rough. They removed the spark plugs and had found two fouled; so they replaced all the spark plugs. They then ran it up a second time and it seemed fine. I loaded the aircraft according to my weight and balance plan then accomplished the pre-flight. The aircraft was already fueled when we arrived.I received my taxi clearance and proceeded to taxi while ground informed me that my clearance was still good. I informed them I would be ready to copy it in the run-up area. During run-up the right magneto was slightly lower than the left; but within the max drop and within 50 RPM of the left. The prop cycle was normal; all engine instruments looked good. I was to climb to 4;000 and expect 6;000 10 minutes after departure. I contacted tower and was assigned a transponder code and asked to hold for IFR release. Shortly after that conversation a small jet landed and I was cleared for takeoff. The climb power setting was 23 inches of map at 2;400 rpms. The cowl flaps were left full open for climb. At 3;000 MSL I leaned the engine. After leaning I was showing 90 KIAS and about 500 FPM climb. At 3;900 MSL approach cleared me to climb to 6;000 MSL. I leveled off at 6;000 MSL and I ran the cruise checklist. Power was set to 21 inches of map at 2;400 RPM. The mixture was leaned to 50F rich of peak egt as per cessna's pilot's operating handbook. The cowl flap was closed as called for in the check list. Chts were normal and the oil was about 75% up to max oil temp. I was then handed off to approach. About a mile from the VOR I started setting up for my turn to heading 250. The engine dropped off; line similar to when you lean an aircraft engine too much and starve it of fuel; then came back on like nothing had happened. I started a scan of the engine instruments. Everything seemed normal to me except that the egt was now at 25F rich of peak egt. I started to enrich the mixture back to 50F rich of peak egt when the aircraft started to shake violently. I called approach with; 'mayday; mayday; mayday; we're losing our engine turning for ZZZ now.' approach advised me that ZZZ was 20 NM away and that ZZZ1 was 10 NM west of us. I asked him for vectors while I changed my map from the IFR low enroute chart to the VFR sectional chart to help me find the airport. I set the mixture full rich; made sure the prop was still at 2;400 RPM and set full power on the throttle. I was able to make 22 inches of map; but could only hold altitude at 4;900 MSL at 100 KIAS. Once on ZZZ1 CTAF I called out that I was overhead at 4;900 MSL circling clockwise for an emergency landing. I circled over the arrival end on the runway at about a 30 degree bank at 18 inches of map. The engine was running smooth at this time like nothing was wrong. I started to think that it might have been a lose spark plug or a problem with the carburetor. I made sure that my passengers were ok and told them that we were over the runway and going to land; that everything would be okay. I pitched for about 110 KIAS and lowered the gear. I then ran the before landing checklist and checked my chart for the field elevation. At high key I set the flaps to 10 degrees. At low key I started to reduce the power and the engine started shaking violently again I tried carb heat but that didn't help. I tried adding power for 18 inches of map but that caused even greater shaking. So; I cut the power to idle applied full flaps and turned for the numbers. I held 80 KIAS until flare andcalled on final for runway 22. We landed and I turned off the runway. I pulled the mixture to the full lean position and coasted to a safe distance from the runway then stopped. [Later] I talked to the mechanic that I had talked to before I departed. He told me that [the FBO] had found that two of the push rods had bent in flight. I feel that there may have been engine damage from a previous flight or flights. Rather than reserving this aircraft for cross country flights the FBO mainly uses this aircraft for complex; commercial; or CFI training. That may have caused heat damage from slow flights at high power settings and multiple climbs and descents going from full power to idle power. Most other fbos I have flown at do not allow C182s to be used for that type of training.

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Original NASA ASRS Text

Title: C182 pilot experiences a rough running engine at 6;000 FT and accepts vectors to the nearest suitable airport. Arriving overhead at 4;900 FT with the engine still producing power; a gliding circling approach is planned and executed successfully. Maintenance discovers that bent pushrods were the cause of the rough running engine.

Narrative: While I was parking I noticed that the aircraft was on the ramp being worked on. I walked out and asked the Mechanic if everything was ok and he told me that everything was good and that he would be finished with the new spark plugs shortly. They finished working on the aircraft and ran the engine up. Everything sounded fine to me from where I was standing. I talked to the Mechanic about the airplane. He told me that they had changed the oil and when they ran it up it had been running rough. They removed the spark plugs and had found two fouled; so they replaced all the spark plugs. They then ran it up a second time and it seemed fine. I loaded the aircraft according to my weight and balance plan then accomplished the pre-flight. The aircraft was already fueled when we arrived.I received my taxi clearance and proceeded to taxi while Ground informed me that my clearance was still good. I informed them I would be ready to copy it in the run-up area. During run-up the right magneto was slightly lower than the left; but within the max drop and within 50 RPM of the left. The prop cycle was normal; all engine instruments looked good. I was to climb to 4;000 and expect 6;000 10 minutes after departure. I contacted Tower and was assigned a transponder code and asked to hold for IFR release. Shortly after that conversation a small jet landed and I was cleared for takeoff. The climb power setting was 23 inches of MAP at 2;400 RPMs. The cowl flaps were left full open for climb. At 3;000 MSL I leaned the engine. After leaning I was showing 90 KIAS and about 500 FPM climb. At 3;900 MSL Approach cleared me to climb to 6;000 MSL. I leveled off at 6;000 MSL and I ran the cruise checklist. Power was set to 21 inches of MAP at 2;400 RPM. The mixture was leaned to 50F rich of peak EGT as per Cessna's Pilot's Operating Handbook. The cowl flap was closed as called for in the check list. CHTs were normal and the OIL was about 75% up to Max Oil Temp. I was then handed off to Approach. About a mile from the VOR I started setting up for my turn to heading 250. The engine dropped off; line similar to when you lean an aircraft engine too much and starve it of fuel; then came back on like nothing had happened. I started a scan of the engine instruments. Everything seemed normal to me except that the EGT was now at 25F rich of peak EGT. I started to enrich the mixture back to 50F rich of peak EGT when the aircraft started to shake violently. I called Approach with; 'Mayday; Mayday; Mayday; we're losing our engine turning for ZZZ now.' Approach advised me that ZZZ was 20 NM away and that ZZZ1 was 10 NM west of us. I asked him for vectors while I changed my map from the IFR low enroute chart to the VFR sectional chart to help me find the airport. I set the mixture full rich; made sure the prop was still at 2;400 RPM and set full power on the throttle. I was able to make 22 inches of MAP; but could only hold altitude at 4;900 MSL at 100 KIAS. Once on ZZZ1 CTAF I called out that I was overhead at 4;900 MSL circling clockwise for an emergency landing. I circled over the arrival end on the runway at about a 30 degree bank at 18 inches of MAP. The engine was running smooth at this time like nothing was wrong. I started to think that it might have been a lose spark plug or a problem with the carburetor. I made sure that my passengers were OK and told them that we were over the runway and going to land; that everything would be okay. I pitched for about 110 KIAS and lowered the gear. I then ran the before landing checklist and checked my chart for the field elevation. At high key I set the flaps to 10 degrees. At low key I started to reduce the power and the engine started shaking violently again I tried carb heat but that didn't help. I tried adding power for 18 inches of MAP but that caused even greater shaking. So; I cut the power to idle applied full flaps and turned for the numbers. I held 80 KIAS until flare andcalled on final for Runway 22. We landed and I turned off the runway. I pulled the mixture to the full lean position and coasted to a safe distance from the runway then stopped. [Later] I talked to the Mechanic that I had talked to before I departed. He told me that [the FBO] had found that two of the push rods had bent in flight. I feel that there may have been engine damage from a previous flight or flights. Rather than reserving this aircraft for cross country flights the FBO mainly uses this aircraft for complex; commercial; or CFI training. That may have caused heat damage from slow flights at high power settings and multiple climbs and descents going from full power to idle power. Most other FBOs I have flown at do not allow C182s to be used for that type of training.

Data retrieved from NASA's ASRS site 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.