Narrative:

I was giving a new hire CFI a chkout in the katana DA20-C1. When approximately 9 mi south of islip, the engine suddenly lost power (down to about 25%). This was enough to only maintain altitude (1500 ft) and an airspeed of 75 KIAS (down from 130 KTS). The instructor/a&P and myself didn't know what the cause could have been. We thought something mechanical was broken, such as a push rod, a valve, or piston rod. Needless to say, I decided frg would be a careless choice. I remember what my old chief pilot once said, 'never bypass a good field,' so I immediately turned right toward islip. En route, we pulled out the poh and did the checklist for partial power and nothing worked (so much for checklists). On initial contact with new york approach, we were told to remain clear of class C airspace (I guess he was too busy). I told him we had engine roughness and required a precautionary landing. He gave us clearance and handed us over to isp tower. Isp was using runway 15R and tower cleared us to land, but since we were coming from the south, this would require us to enter downwind, base to final. I told him we were going to land straight-in runway 33L in order to save time. He then cleared us to land runway 33L. At no time did I declare an emergency, as we were maintaining our altitude and slowly -- very slowly -- we were getting some more power (from 1600 RPM to 2000 RPM). But the tower said 'they did,' which I am still confused about. Upon landing, we took cowling off and didn't see any mechanical damage in the engine. The engine was running fine. After no less than 4 real good runups, we decided to take off towards frg. The flight was uneventful. The instructor/a&P suspects it was carbon deposits on the valves which gave us loss of power. The plane still flies today.

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Original NASA ASRS Text

Title: A KATANA DA-20 LOST PWR AND MADE AN EMER LNDG AT ISP.

Narrative: I WAS GIVING A NEW HIRE CFI A CHKOUT IN THE KATANA DA20-C1. WHEN APPROX 9 MI S OF ISLIP, THE ENG SUDDENLY LOST PWR (DOWN TO ABOUT 25%). THIS WAS ENOUGH TO ONLY MAINTAIN ALT (1500 FT) AND AN AIRSPD OF 75 KIAS (DOWN FROM 130 KTS). THE INSTRUCTOR/A&P AND MYSELF DIDN'T KNOW WHAT THE CAUSE COULD HAVE BEEN. WE THOUGHT SOMETHING MECHANICAL WAS BROKEN, SUCH AS A PUSH ROD, A VALVE, OR PISTON ROD. NEEDLESS TO SAY, I DECIDED FRG WOULD BE A CARELESS CHOICE. I REMEMBER WHAT MY OLD CHIEF PLT ONCE SAID, 'NEVER BYPASS A GOOD FIELD,' SO I IMMEDIATELY TURNED R TOWARD ISLIP. ENRTE, WE PULLED OUT THE POH AND DID THE CHKLIST FOR PARTIAL PWR AND NOTHING WORKED (SO MUCH FOR CHKLISTS). ON INITIAL CONTACT WITH NEW YORK APCH, WE WERE TOLD TO REMAIN CLR OF CLASS C AIRSPACE (I GUESS HE WAS TOO BUSY). I TOLD HIM WE HAD ENG ROUGHNESS AND REQUIRED A PRECAUTIONARY LNDG. HE GAVE US CLRNC AND HANDED US OVER TO ISP TWR. ISP WAS USING RWY 15R AND TWR CLRED US TO LAND, BUT SINCE WE WERE COMING FROM THE S, THIS WOULD REQUIRE US TO ENTER DOWNWIND, BASE TO FINAL. I TOLD HIM WE WERE GOING TO LAND STRAIGHT-IN RWY 33L IN ORDER TO SAVE TIME. HE THEN CLRED US TO LAND RWY 33L. AT NO TIME DID I DECLARE AN EMER, AS WE WERE MAINTAINING OUR ALT AND SLOWLY -- VERY SLOWLY -- WE WERE GETTING SOME MORE PWR (FROM 1600 RPM TO 2000 RPM). BUT THE TWR SAID 'THEY DID,' WHICH I AM STILL CONFUSED ABOUT. UPON LNDG, WE TOOK COWLING OFF AND DIDN'T SEE ANY MECHANICAL DAMAGE IN THE ENG. THE ENG WAS RUNNING FINE. AFTER NO LESS THAN 4 REAL GOOD RUNUPS, WE DECIDED TO TAKE OFF TOWARDS FRG. THE FLT WAS UNEVENTFUL. THE INSTRUCTOR/A&P SUSPECTS IT WAS CARBON DEPOSITS ON THE VALVES WHICH GAVE US LOSS OF PWR. THE PLANE STILL FLIES TODAY.

Data retrieved from NASA's ASRS site as of July 2007 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.