Narrative:

I left cos at XA15 on apr/xa/99 with 1 passenger. I was flying a cessna skyhawk 172 built in 1985. We were flying to salida, co, which is a 1 hour flight across mountainous terrain. The flight to salida (OV2) was uneventful. The engine was hard to start in OV2. It took 4-5 attempts before it would turn over. I have had this happen a number of times with 172's, and thought nothing of it. Usually, it is caused by flooding the engine, not enough primer, or low battery power. We lifted off on runway 6 and headed north to buena vista. Just outside buena vista, I turned east intending to cross over trout creek pass. We crossed the pass at 11000 ft MSL. Over an area known as south park, not too far from antero reservoir, I noticed the propeller sounded different. I began to suspect there might be a problem. At one point, the cowling began to vibrate. I noticed we were traveling at 110 KIAS, and the RPM's were down to 2200 RPM. I suspected carburetor icing and pulled on full carburetor heat. RPM's immediately dropped about 150 RPM. I left the carburetor heat on for 5-6 mins with no improvement. Meanwhile, I was adjusting the mixture. I had already leaned the mixture quite a bit before crossing trout creek pass. I leaned it some more, but there was no improvement. I enriched it, no improvement. I continued to work with the mixture, going from lean to rich, with no success. I did not do a magneto check, nor did I think to check the primer. A few mi west of divide, co, the RPM's dropped below 2000 RPM. The engine sounded very poor, as if it were out of sync. My airspeed had now dropped to 85 KIAS. I saw that the situation was deteriorating, and made a decision to make a precautionary landing. I called in a mayday over the cos approach frequency of 124.0. The tower acknowledged and gave me a squawk code. I advised the tower that I was experiencing loss of engine power and would land in a field outside divide. The controller was very helpful and reassuring. He advised me of several good landing sites outside divide, and warned me of the power lines. I circled and looked for a good landing site along highway 67. I spotted a dirt road and thought I might be able to land there. A pickup truck, which had been off to the side of the road, pulled out onto the road. So I abandoned that plan, and headed for a field just east of highway 67. As I circled over my landing site, I pulled back some power to prepare for landing. The engine sounded very sick and out of sync. I turned to final going about 70 KIAS and touched down in the field at 65 KIAS. We hit pretty hard and then bumped and pitched across the field, down a small incline, back up the other side, and then came to rest about 50 ft in front of another incline. I finally hit the brakes hard and we came to a stop. We were both wearing seat belts and shoulder harnesses. We had no injuries and no bruises, just a little shaken. The airplane had no visible damage. Mechanical problem: a mechanic and the airplane's owner drove up to cos to the site. The mechanic checked the spark plugs and found the #1 cylinder plug to be coated with oil. He pulled the rocker arm cover, removed the rocker arms and the push rod, and eventually removed the tappet. He noticed that the exhaust valve tappet was not performing well, and concluded that it was stuck. After cleaning up the tappet and replacing it, the owner was able to start the engine and get it up to 2200 RPM. The owner then took off from the field and flew the plane back to cos. He said the engine acted up again when he pulled the power to land at cos. After the flight, I found out that a piston skirt in another cylinder had shredded some metal about 3 weeks before this incident. The piston had been replaced. In light of the piston problem and the stuck tappet, the mechanic recommended that all the cylinders be examined, and that the engine be overhauled or replaced. Even though I have performed some 50 simulated emergency lndgs, I still did not follow all of the procedures which I had learned. I was so focused on flying the plane and getting it down, that my mind ignored everything else. From now on, when I fly, I will place the emergency checklist in a prominent place in the cockpit. Also, it might make more sense, during emergency landing practice, to fly over an airstrip, actually touch down, and practice using the brakes to stop the plane as quickly as possible.

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Original NASA ASRS Text

Title: FEARING IMPENDING ENG FAILURE, PVT PLT OF SINGLE ENG ACFT, FLYING OVER MOUNTAINOUS TERRAIN, MAKES EMER LNDG IN A FIELD.

Narrative: I LEFT COS AT XA15 ON APR/XA/99 WITH 1 PAX. I WAS FLYING A CESSNA SKYHAWK 172 BUILT IN 1985. WE WERE FLYING TO SALIDA, CO, WHICH IS A 1 HR FLT ACROSS MOUNTAINOUS TERRAIN. THE FLT TO SALIDA (OV2) WAS UNEVENTFUL. THE ENG WAS HARD TO START IN OV2. IT TOOK 4-5 ATTEMPTS BEFORE IT WOULD TURN OVER. I HAVE HAD THIS HAPPEN A NUMBER OF TIMES WITH 172'S, AND THOUGHT NOTHING OF IT. USUALLY, IT IS CAUSED BY FLOODING THE ENG, NOT ENOUGH PRIMER, OR LOW BATTERY PWR. WE LIFTED OFF ON RWY 6 AND HEADED NORTH TO BUENA VISTA. JUST OUTSIDE BUENA VISTA, I TURNED E INTENDING TO CROSS OVER TROUT CREEK PASS. WE CROSSED THE PASS AT 11000 FT MSL. OVER AN AREA KNOWN AS SOUTH PARK, NOT TOO FAR FROM ANTERO RESERVOIR, I NOTICED THE PROP SOUNDED DIFFERENT. I BEGAN TO SUSPECT THERE MIGHT BE A PROB. AT ONE POINT, THE COWLING BEGAN TO VIBRATE. I NOTICED WE WERE TRAVELING AT 110 KIAS, AND THE RPM'S WERE DOWN TO 2200 RPM. I SUSPECTED CARB ICING AND PULLED ON FULL CARB HEAT. RPM'S IMMEDIATELY DROPPED ABOUT 150 RPM. I LEFT THE CARB HEAT ON FOR 5-6 MINS WITH NO IMPROVEMENT. MEANWHILE, I WAS ADJUSTING THE MIXTURE. I HAD ALREADY LEANED THE MIXTURE QUITE A BIT BEFORE XING TROUT CREEK PASS. I LEANED IT SOME MORE, BUT THERE WAS NO IMPROVEMENT. I ENRICHED IT, NO IMPROVEMENT. I CONTINUED TO WORK WITH THE MIXTURE, GOING FROM LEAN TO RICH, WITH NO SUCCESS. I DID NOT DO A MAGNETO CHK, NOR DID I THINK TO CHK THE PRIMER. A FEW MI W OF DIVIDE, CO, THE RPM'S DROPPED BELOW 2000 RPM. THE ENG SOUNDED VERY POOR, AS IF IT WERE OUT OF SYNC. MY AIRSPD HAD NOW DROPPED TO 85 KIAS. I SAW THAT THE SITUATION WAS DETERIORATING, AND MADE A DECISION TO MAKE A PRECAUTIONARY LNDG. I CALLED IN A MAYDAY OVER THE COS APCH FREQ OF 124.0. THE TWR ACKNOWLEDGED AND GAVE ME A SQUAWK CODE. I ADVISED THE TWR THAT I WAS EXPERIENCING LOSS OF ENG PWR AND WOULD LAND IN A FIELD OUTSIDE DIVIDE. THE CTLR WAS VERY HELPFUL AND REASSURING. HE ADVISED ME OF SEVERAL GOOD LNDG SITES OUTSIDE DIVIDE, AND WARNED ME OF THE PWR LINES. I CIRCLED AND LOOKED FOR A GOOD LNDG SITE ALONG HWY 67. I SPOTTED A DIRT ROAD AND THOUGHT I MIGHT BE ABLE TO LAND THERE. A PICKUP TRUCK, WHICH HAD BEEN OFF TO THE SIDE OF THE ROAD, PULLED OUT ONTO THE ROAD. SO I ABANDONED THAT PLAN, AND HEADED FOR A FIELD JUST E OF HWY 67. AS I CIRCLED OVER MY LNDG SITE, I PULLED BACK SOME PWR TO PREPARE FOR LNDG. THE ENG SOUNDED VERY SICK AND OUT OF SYNC. I TURNED TO FINAL GOING ABOUT 70 KIAS AND TOUCHED DOWN IN THE FIELD AT 65 KIAS. WE HIT PRETTY HARD AND THEN BUMPED AND PITCHED ACROSS THE FIELD, DOWN A SMALL INCLINE, BACK UP THE OTHER SIDE, AND THEN CAME TO REST ABOUT 50 FT IN FRONT OF ANOTHER INCLINE. I FINALLY HIT THE BRAKES HARD AND WE CAME TO A STOP. WE WERE BOTH WEARING SEAT BELTS AND SHOULDER HARNESSES. WE HAD NO INJURIES AND NO BRUISES, JUST A LITTLE SHAKEN. THE AIRPLANE HAD NO VISIBLE DAMAGE. MECHANICAL PROB: A MECH AND THE AIRPLANE'S OWNER DROVE UP TO COS TO THE SITE. THE MECH CHKED THE SPARK PLUGS AND FOUND THE #1 CYLINDER PLUG TO BE COATED WITH OIL. HE PULLED THE ROCKER ARM COVER, REMOVED THE ROCKER ARMS AND THE PUSH ROD, AND EVENTUALLY REMOVED THE TAPPET. HE NOTICED THAT THE EXHAUST VALVE TAPPET WAS NOT PERFORMING WELL, AND CONCLUDED THAT IT WAS STUCK. AFTER CLEANING UP THE TAPPET AND REPLACING IT, THE OWNER WAS ABLE TO START THE ENG AND GET IT UP TO 2200 RPM. THE OWNER THEN TOOK OFF FROM THE FIELD AND FLEW THE PLANE BACK TO COS. HE SAID THE ENG ACTED UP AGAIN WHEN HE PULLED THE PWR TO LAND AT COS. AFTER THE FLT, I FOUND OUT THAT A PISTON SKIRT IN ANOTHER CYLINDER HAD SHREDDED SOME METAL ABOUT 3 WKS BEFORE THIS INCIDENT. THE PISTON HAD BEEN REPLACED. IN LIGHT OF THE PISTON PROB AND THE STUCK TAPPET, THE MECH RECOMMENDED THAT ALL THE CYLINDERS BE EXAMINED, AND THAT THE ENG BE OVERHAULED OR REPLACED. EVEN THOUGH I HAVE PERFORMED SOME 50 SIMULATED EMER LNDGS, I STILL DID NOT FOLLOW ALL OF THE PROCS WHICH I HAD LEARNED. I WAS SO FOCUSED ON FLYING THE PLANE AND GETTING IT DOWN, THAT MY MIND IGNORED EVERYTHING ELSE. FROM NOW ON, WHEN I FLY, I WILL PLACE THE EMER CHKLIST IN A PROMINENT PLACE IN THE COCKPIT. ALSO, IT MIGHT MAKE MORE SENSE, DURING EMER LNDG PRACTICE, TO FLY OVER AN AIRSTRIP, ACTUALLY TOUCH DOWN, AND PRACTICE USING THE BRAKES TO STOP THE PLANE AS QUICKLY AS POSSIBLE.

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.