Narrative:

Aircraft had been flown the previous day in preparation for the long flight to ensure it was functioning well. After 40 minutes of practice; I felt everything was working fine. On the day of the flight on climbout after clearing the cloud layer at 2000 ft; I was advised to level out at 4000 ft for traffic before continuing climb to our filed 9500 ft. Shortly after closing cowl flaps and trimming plane; a loud boom and shaking was felt. A second later I heard a rattling metal sound. The passengers said (later on the ground) that they smelled fuel. I started to reduce power and set prop to high RPM setting and noticed that prop control knob was bent up. I assumed a prop control or other mechanical problem and declared an emergency with ATC asking for a return to the departure airport and vectors to the final for the ILS. Once on course; since my approach charts were on the cabin floor; I decided to focus on flying and asked ATC for the frequency for the ILS and the final approach course (not trusting my memory). After breaking out high over the field; I asked tower for a 360 to lose altitude and landed uneventfully. I taxied to the nearest shop and we began looking for the problem. The right rear portion of the engine compartment was coated in black and we assumed a blown cylinder. We found the cowling flaps were both open (and I had closed them for cruise as I approached 7000 ft); and I noticed that the right flap was extended further than the left. When I looked back at the panel; I found that not only had one prop control bent upwards; but the cowling flap control had as well. After removing all of the cowling; no indication of any failed component could be found; but the black extended out the length of the fuselage. The mechanic found what looked like a melted straw hanging on one of the cables. Then we noticed that the black film was too thick to be exhaust and certainly was not oil. It was black paint. The mechanic suggested someone had left a paint can in the engine compartment and it had exploded as the engine heated up and we started to reach altitude. He said aerosol cans have similar straws inside them from the nozzle to the bottom of the can. This was the first long flight after the last time the cowling had been removed from the aircraft so we investigated adding an oil filter to the engine. I had used a can sitting on the workbench as a model for an oil filter to judge if it would be easy to replace at oil changes. The picture made total sense. The explosive force pushed the right cowl flap open. That yanked the cowl flap control to the open position and then ripped the cable out of the keeper and pulled it further. The cowl cable was tied to the prop control cable under the panel. This bent both of them upwards. The 'fuel' smell my passengers mentioned was the aerosol spray and pant fumes; the mechanical rattle I heard was the paint can exiting out the right cowling flap. We always count the tools we use when working on the aircraft to ensure nothing is left behind. I guess we need to add aerosol cans to that checklist.

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Original NASA ASRS Text

Title: A C182 Pilot reported that he left a can of spray paint in the aircraft's engine compartment and during climbout it exploded causing both the propeller control and engine cowling to change positions. The event felt like an engine malfunction so an emergency was declared and the aircraft returned to land.

Narrative: Aircraft had been flown the previous day in preparation for the long flight to ensure it was functioning well. After 40 minutes of practice; I felt everything was working fine. On the day of the flight on climbout after clearing the cloud layer at 2000 FT; I was advised to level out at 4000 FT for traffic before continuing climb to our filed 9500 FT. Shortly after closing cowl flaps and trimming plane; a loud boom and shaking was felt. A second later I heard a rattling metal sound. The passengers said (later on the ground) that they smelled fuel. I started to reduce power and set prop to high RPM setting and noticed that prop control knob was bent up. I assumed a prop control or other mechanical problem and declared an emergency with ATC asking for a return to the departure airport and vectors to the final for the ILS. Once on course; since my approach charts were on the cabin floor; I decided to focus on flying and asked ATC for the frequency for the ILS and the final approach course (not trusting my memory). After breaking out high over the field; I asked tower for a 360 to lose altitude and landed uneventfully. I taxied to the nearest shop and we began looking for the problem. The right rear portion of the engine compartment was coated in black and we assumed a blown cylinder. We found the cowling flaps were both open (and I had closed them for cruise as I approached 7000 FT); and I noticed that the right flap was extended further than the left. When I looked back at the panel; I found that not only had one prop control bent upwards; but the cowling flap control had as well. After removing all of the cowling; no indication of any failed component could be found; but the black extended out the length of the fuselage. The mechanic found what looked like a melted straw hanging on one of the cables. Then we noticed that the black film was too thick to be exhaust and certainly was not oil. It was black paint. The mechanic suggested someone had left a paint can in the engine compartment and it had exploded as the engine heated up and we started to reach altitude. He said aerosol cans have similar straws inside them from the nozzle to the bottom of the can. This was the first long flight after the last time the cowling had been removed from the aircraft so we investigated adding an oil filter to the engine. I had used a can sitting on the workbench as a model for an oil filter to judge if it would be easy to replace at oil changes. The picture made total sense. The explosive force pushed the right cowl flap open. That yanked the cowl flap control to the open position and then ripped the cable out of the keeper and pulled it further. The cowl cable was tied to the prop control cable under the panel. This bent both of them upwards. The 'fuel' smell my passengers mentioned was the aerosol spray and pant fumes; The mechanical rattle I heard was the paint can exiting out the right cowling flap. We always count the tools we use when working on the aircraft to ensure nothing is left behind. I guess we need to add aerosol cans to that checklist.

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.