A C152 PLT LOSES PWR AFTER TKOF AND MAKES AN OFF ARPT EMER LNDG NEAR THE DEP ARPT; A MIL GRASS SURFACED FIELD; JUST NW OF EGLL; FO.

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A C152 HAD JUST RETURNED FROM A FLT; WENT DIRECT TO THE PUMPS -- FULL TANKS. I TOOK OVER THE ACFT AFTER ABOUT 5 MINS. IT STILL FELT HOT AND ALL GAUGES WERE IN THE GREEN. I DID MY PREFLT CHKS; INCLUDING A PHYSICAL OF THE TANKS FOR WATER AND FULL. I CALLED FOR TAXI AND WENT BRISKLY TO THE HOLD FOR RWY 26. (I USUALLY TAXI WITH CARB HEAT; BUT CANNOT REMEMBER IF I DID ON THIS OCCASION.) I DID MY PRETKOF CHKS; INCLUDING CARB HEAT AND MAGNETOS -- ALL SEEMED NORMAL. I DEPARTED RWY 26. IT WAS MARGINALLY SLUGGISH; BUT I PUT THIS DOWN TO HIGH MOISTURE; WET GRASS; AND THE UPHILL SLOPE. ALL SEEMED NORMAL; IF A BIT SLUGGISH. I CLBED OUT ON RWY 26; CHANGED TO ABOUT 20 DEG HDG AFTER ABOUT 1/2 MI FOR VILLAGE NOISE ABATEMENT. AT ABOUT 1 - 1 1/2 MI OUT AND ABOUT 400-500 FT; THE ENG QUIT. THERE WAS NO MISSING OR CHANGE OF ENG NOTE; JUST A DEAD STOP. HAVING NOTICED A GOOD FIELD FOR EFATO ON THE CLBOUT; I TURNED BACK THROUGH 130 DEGS L; ESTABLISHED MYSELF ON A DIAGONAL BASE; PUT DOWN 10 DEG FLAPS; TURNED LATE FINAL AND LANDED ABOUT 18 DEG HDG (S). I CHKED THE ACFT CTLS AND FOUND THE MIXTURE FULL WEAK. PUSHED IT FORWARD FULL RICH; GOT OUT; CHKED THE 3 DRAINS FOR WATER -- NONE WAS PRESENT. I THEN TRIED TO START THE ENG. IT RAN 3 BEATS AND STOPPED; AND WOULD NOT START WHEN I TRIED AGAIN. I DID NOTHING FURTHER TO THE ACFT. IT WAS CATEGORICALLY STATED BY THE MGMNT OF THE AIRPLANE CLUB THAT IT WAS CARB ICE. WHILE I WOULD AGREE THAT THIS WAS POSSIBLE; THE SYMPTOMS WERE NOT THOSE YOU WOULD EXPECT. I ENCLOSE THEIR RPT TO THE UNITED KINGDOM CAA. TKOF CHKS WERE CARRIED OUT; AND EVEN IF THE PLT WAS CARELESS (MYSELF) CARB ICE AT THIS TIME WOULD HAVE CAUSED A NOTICEABLE CHANGE IN THE IDLE SPD; AND ROUGH RUNNING ON MAGNETO CHK. I WOULD HAVE REACTED VERY STRONGLY TO THIS PROMPT. TKOF PWR IS AN UNUSUAL ENVIRONMENT FOR CARB ICE. CARB ICE USUALLY PRESENTS WITH A GRADUAL DECREASE OF PWR WITH IRREGULAR RUNNING. THIS WAS NOT IN EVIDENCE. THE POSSIBILITIES WERE AS I SEE IT: 1) A PIECE OF GUM OR CEMENT IN THE CARB TEMPORARILY STUCK IN THE JET. 2) I PULLED THE MIXTURE ACCIDENTALLY; AND THE EVIDENCE WAS MASKED BY NOT HAVING TIME TO EFFECT THE EFATO CHKS; AS I HAD TO DO THE CHKS FOR EFATO LNDG AND THE MIXTURE WAS PULLED IMMEDIATELY AS AN INADVERTENT START AND FIRE PRECAUTION. THIS CAUSE VERY UNLIKELY AS I WAS NOT AT CIRCUIT HT; AND EVEN AS A BE-KIND-TO-THE-ACFT ACTION IT WOULD HAVE BEEN IMPOSSIBLE TO DO IT WITHOUT ASSOCIATING THE CUTOUT WITH THE THROTTLE ACTION; AND THOUGH I HAVE BEEN IN THE PAST TAUGHT TO DO THIS; I HAVE NOT DONE SO FOR MANY YRS. 3) IT WAS CARB ICE AND MY BEING USED TO A HVY 40 HP MOTOR GLIDER HAD MASKED THE PERFORMANCE DETERIORATION. I HAVE BROUGHT THIS TO YOUR ATTN AS IF IT WAS INDEED CARB ICE THEN NONE OF US HAVE ANY PROTECTION FROM THE REAL POSSIBILITY OF AN ENG CUTTING ON A COOL MOIST AUTUMN EVENING.