Narrative:

I departed southwest for a 3-hour banner tow circuit. Upon reaching my destination; I started my circuit patterns at 1;300 feet. The winds at the time were reporting approximately 110 at 19 knots; gusting 25 knots. After two hours at my banner location; I made the decision to come back to the airport early due to the up and down draft thermals and gusty winds. I was ordered by the tower to maintain at or below 1;500 feet. However; the thermals I was constantly fighting to maintain altitude were forcing me to bring my power to idle after turning my carb heat on in order to descend back down to 1;300 feet. I used carburetor heat multiple times throughout the flight. After two hours of fighting with the thermals I decided to return to base an hour early. I then advised the tower that I was done with my banner operations. Tower then vectored me west and then once I was far west enough; they cleared me for a northbound turn back to the airport. Soon after; tower told me to squawk VFR and to change frequencies. At that time; I got the ATIS information then switched to the tower frequency. While still trying to maintain 1;300 feet; I noticed that I was at 1;200 feet; so I reached for my throttle to slightly increase power to get back up to 1;300 feet; but there was no response. I immediately noticed the lack of response. At that time I was at 1;000 feet; so I again applied my carburetor heat and waited a few seconds as I continued to lose altitude. At approximately 700 feet I turned my fuel pump on and put my mixture rich. Immediately after going mixture rich I lost almost all of my power. At this time; I was rapidly losing altitude so I immediately released the banner and started looking for a place to land. Right after that; I advised the tower of my engine failure and location. They responded telling me to 'squawk ident'; I replied back 'ident' and repeated my location and that I was going down. At about 300 feet I had lost my radio signal with [the tower] so I was focused on making a controlled landing in the water and luckily right before impact I was able to lock my seat belt harness and prepare for impact. After the plane settled; water immediately started to fill the cockpit so I rushed to get my harness unfastened and extracted my way out of the airplane and waited for help.I honestly don't know what caused the engine failure; but I don't think it was carburetor icing because I used my carburetor heat multiple times throughout the flight. The thermals shot my plane up 100-200 feet numerous times and in order to descend back down to 1;300 feet I would have to take my power to idle which would force me to use my carb heat.

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Original NASA ASRS Text

Title: The pilot of a Piper Pawnee experienced an engine problem while towing a banner; resulting in an off-field landing in the water.

Narrative: I departed southwest for a 3-hour banner tow circuit. Upon reaching my destination; I started my circuit patterns at 1;300 feet. The winds at the time were reporting approximately 110 at 19 knots; gusting 25 knots. After two hours at my banner location; I made the decision to come back to the airport early due to the up and down draft thermals and gusty winds. I was ordered by the Tower to maintain at or below 1;500 feet. However; the thermals I was constantly fighting to maintain altitude were forcing me to bring my power to idle after turning my carb heat on in order to descend back down to 1;300 feet. I used carburetor heat multiple times throughout the flight. After two hours of fighting with the thermals I decided to return to base an hour early. I then advised the Tower that I was done with my banner operations. Tower then vectored me west and then once I was far west enough; they cleared me for a northbound turn back to the airport. Soon after; Tower told me to squawk VFR and to change frequencies. At that time; I got the ATIS information then switched to the Tower frequency. While still trying to maintain 1;300 feet; I noticed that I was at 1;200 feet; so I reached for my throttle to slightly increase power to get back up to 1;300 feet; but there was no response. I immediately noticed the lack of response. At that time I was at 1;000 feet; so I again applied my carburetor heat and waited a few seconds as I continued to lose altitude. At approximately 700 feet I turned my fuel pump on and put my mixture rich. Immediately after going mixture rich I lost almost all of my power. At this time; I was rapidly losing altitude so I immediately released the banner and started looking for a place to land. Right after that; I advised the Tower of my engine failure and location. They responded telling me to 'Squawk Ident'; I replied back 'Ident' and repeated my location and that I was going down. At about 300 feet I had lost my radio signal with [the Tower] so I was focused on making a controlled landing in the water and luckily right before impact I was able to lock my seat belt harness and prepare for impact. After the plane settled; water immediately started to fill the cockpit so I rushed to get my harness unfastened and extracted my way out of the airplane and waited for help.I honestly don't know what caused the engine failure; but I don't think it was carburetor icing because I used my carburetor heat multiple times throughout the flight. The thermals shot my plane up 100-200 feet numerous times and in order to descend back down to 1;300 feet I would have to take my power to idle which would force me to use my carb heat.

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.