Narrative:

I was getting ready for my long cross country flight. In my planning; I have planned to stop at an intermediate airport for refueling. During preflight when I was taking fuel sample; I have found little bubbles of water in the fuel sump. I drained all the water and took another sample that did not have any water in it. I started my flight and headed south. I climbed to 6500 ft MSL; VFR cruising altitude. Weather was clear to the south and visibility more than 10 SM with clouds to the west of my route. After approximately 50 minutes of cruising at 2500 RPM and 100 knots indicated airspeed in C152; I contacted approach. I asked for flight following to continue my flight to my first stop for refueling. Once I got flight following; I flew for about 3-5 minutes. And then my RPM dropped from 2500 to 2300 and accelerated back to 2500. I quickly checked both magnetos several times. During the mag check; RPM would still sometimes drop 100-300 RPM and then accelerate back to normal. For the next couple minutes the engine was running fine. At that time I checked the mixture; oil pressure; fuel indicators; and fuel selector and decreased RPM to 2300. I checked the mags again and they worked fine. After I checked everything RPM dropped from 2300 to 1800 or maybe even more and accelerated back to normal. Then approach talked to me and I decided to tell them that I'm experiencing engine problems and would like to land. They asked me if I 'm declaring emergency and I said yes. Approach asked me to describe the situation and say how much fuel I have on board. I told them I had more than half tanks and that my RPM drops and accelerates back. Then I decided to squawk an emergency code; 7700; but by mistake squawked 7500 and did not notice it. That created more problems. Approach asked me how many people I had on board and I said 1. They informed me of current weather and winds at a nearby airport and wanted me to contact them on ground. I changed frequency and announced myself on CTAF frequency. Descending down on long base I was at 80 knots at almost idle power settling. It seemed like the engine would still sometimes loose power even at idle setting. But because I was very high I didn't worry about it much. The runway was right in from of me; so I quickly descended and landed. After I landed the engine was running fine and I had no problems taxiing to parking. I shut the engine off when I arrived to the parking spot and contacted approach and explained to them everything. When our school instructor and mechanic came down to pick me up; they found some water when they inspected the engine. We still don't know the real cause of RPM drop; but most likely it was water. What I learned from my situation is to take more fuel samples before the flight and be more careful when squawking an emergency code. Other than that I'm thankful that everything went well. Thanks to everyone who helped me out and thanks to god I'm alive.

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Original NASA ASRS Text

Title: A C152 pilot on a cross country declared an emergency and landed after the engine began surging. During preflight water was drained from the fuel tank. After his landing more water was found and suspected as the source of the engine's surges.

Narrative: I was getting ready for my long cross country flight. In my planning; I have planned to stop at an intermediate airport for refueling. During preflight when I was taking fuel sample; I have found little bubbles of water in the fuel sump. I drained all the water and took another sample that did not have any water in it. I started my flight and headed south. I climbed to 6500 FT MSL; VFR cruising altitude. Weather was clear to the south and visibility more than 10 SM with clouds to the west of my route. After approximately 50 minutes of cruising at 2500 RPM and 100 knots indicated airspeed in C152; I contacted Approach. I asked for flight following to continue my flight to my first stop for refueling. Once I got flight following; I flew for about 3-5 minutes. And then my RPM dropped from 2500 to 2300 and accelerated back to 2500. I quickly checked both magnetos several times. During the mag check; RPM would still sometimes drop 100-300 RPM and then accelerate back to normal. For the next couple minutes the engine was running fine. At that time I checked the mixture; oil pressure; fuel indicators; and fuel selector and decreased RPM to 2300. I checked the mags again and they worked fine. After I checked everything RPM dropped from 2300 to 1800 or maybe even more and accelerated back to normal. Then Approach talked to me and I decided to tell them that I'm experiencing engine problems and would like to land. They asked me if I 'm declaring emergency and I said yes. Approach asked me to describe the situation and say how much fuel I have on board. I told them I had more than half tanks and that my RPM drops and accelerates back. Then I decided to squawk an emergency code; 7700; but by mistake squawked 7500 and did not notice it. That created more problems. Approach asked me how many people I had on board and I said 1. They informed me of current weather and winds at a nearby airport and wanted me to contact them on ground. I changed frequency and announced myself on CTAF frequency. Descending down on long base I was at 80 knots at almost idle power settling. It seemed like the engine would still sometimes loose power even at idle setting. But because I was very high I didn't worry about it much. The runway was right in from of me; so I quickly descended and landed. After I landed the engine was running fine and I had no problems taxiing to parking. I shut the engine off when I arrived to the parking spot and contacted Approach and explained to them everything. When our school instructor and Mechanic came down to pick me up; they found some water when they inspected the engine. We still don't know the real cause of RPM drop; but most likely it was water. What I learned from my situation is to take more fuel samples before the flight and be more careful when squawking an emergency code. Other than that I'm thankful that everything went well. Thanks to everyone who helped me out and thanks to God I'm alive.

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.