Narrative:

It was a normal training flight with me; a flight instructor; and a student who is training for a light sport pilot certificate. The aircraft is a 1946 ercoupe. We were approaching ZZZ when the engine began to lose power. The engine would surge. It would run well for a second or two and then it would quit. This surging of power kept repeating. It appeared as if something was blocking the fuel from flowing steadily to the carburetor. We were at 5500 ft MSL (1500 ft AGL) when this problem began. We were near an interstate and stayed near it as we began to lose altitude. We tried carburetor heat to no avail. The outside air temperature was around 90 degrees and the humidity was low; so we didn't really expect carburetor heat to help and it didn't. We tried running on left magneto only and on right magneto only and that didn't make much difference either. We tried moving the fuel valve from on to off and then back to on. The off position did shut fuel off; but moving it back to on made the engine continue surging. The access road to the interstate highway was long and straight and we noted a gap in the automotive traffic on it so we elected to land. We brought the power back to idle and made a straight-in approach to the road. The only additional excitement was caused by power lines stretched across the road. We saw them just in time to 'duck' under them and land. The landing was normal. The motorists behind us stopped and helped us push the aircraft off to one side of the road so that traffic could pass by. The FAA sent a designated airworthiness inspector out to look at the plane. He determined that a bracket securing the throttle cable was loose and that this could have allowed the throttle arm on the carburetor to move and thus cause the surging we experienced. We are going to have a mechanic secure the throttle cable and do a thorough inspection to see if he can find anything else that could have caused the engine to behave as it did. We are especially going to have him examine the header fuel tank and the fuel lines to see if there is any foreign matter partially blocking the flow to the carburetor. As our actions; we felt as if we did the right thing landing where we did and when we did. We could have gone a bit farther; but we saw a clear way to a safe landing and we took it. No one was injured and no damage was done to persons or property in the air or on the ground.

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Original NASA ASRS Text

Title: AN INSTRUCTOR AND STUDENT FLYING AN ERCOUPE EXPERIENCED A SURGING ENG AND LANDED ON AN INTERSTATE WHILE PWR REMAINED. A THROTTLE CABLE WAS FOUND LOOSE.

Narrative: IT WAS A NORMAL TRAINING FLT WITH ME; A FLT INSTRUCTOR; AND A STUDENT WHO IS TRAINING FOR A LIGHT SPORT PLT CERTIFICATE. THE ACFT IS A 1946 ERCOUPE. WE WERE APCHING ZZZ WHEN THE ENG BEGAN TO LOSE PWR. THE ENG WOULD SURGE. IT WOULD RUN WELL FOR A SECOND OR TWO AND THEN IT WOULD QUIT. THIS SURGING OF PWR KEPT REPEATING. IT APPEARED AS IF SOMETHING WAS BLOCKING THE FUEL FROM FLOWING STEADILY TO THE CARB. WE WERE AT 5500 FT MSL (1500 FT AGL) WHEN THIS PROB BEGAN. WE WERE NEAR AN INTERSTATE AND STAYED NEAR IT AS WE BEGAN TO LOSE ALT. WE TRIED CARB HEAT TO NO AVAIL. THE OUTSIDE AIR TEMP WAS AROUND 90 DEGS AND THE HUMIDITY WAS LOW; SO WE DIDN'T REALLY EXPECT CARB HEAT TO HELP AND IT DIDN'T. WE TRIED RUNNING ON L MAGNETO ONLY AND ON R MAGNETO ONLY AND THAT DIDN'T MAKE MUCH DIFFERENCE EITHER. WE TRIED MOVING THE FUEL VALVE FROM ON TO OFF AND THEN BACK TO ON. THE OFF POS DID SHUT FUEL OFF; BUT MOVING IT BACK TO ON MADE THE ENG CONTINUE SURGING. THE ACCESS ROAD TO THE INTERSTATE HWY WAS LONG AND STRAIGHT AND WE NOTED A GAP IN THE AUTOMOTIVE TFC ON IT SO WE ELECTED TO LAND. WE BROUGHT THE PWR BACK TO IDLE AND MADE A STRAIGHT-IN APCH TO THE ROAD. THE ONLY ADDITIONAL EXCITEMENT WAS CAUSED BY POWER LINES STRETCHED ACROSS THE ROAD. WE SAW THEM JUST IN TIME TO 'DUCK' UNDER THEM AND LAND. THE LNDG WAS NORMAL. THE MOTORISTS BEHIND US STOPPED AND HELPED US PUSH THE ACFT OFF TO ONE SIDE OF THE ROAD SO THAT TFC COULD PASS BY. THE FAA SENT A DESIGNATED AIRWORTHINESS INSPECTOR OUT TO LOOK AT THE PLANE. HE DETERMINED THAT A BRACKET SECURING THE THROTTLE CABLE WAS LOOSE AND THAT THIS COULD HAVE ALLOWED THE THROTTLE ARM ON THE CARB TO MOVE AND THUS CAUSE THE SURGING WE EXPERIENCED. WE ARE GOING TO HAVE A MECH SECURE THE THROTTLE CABLE AND DO A THOROUGH INSPECTION TO SEE IF HE CAN FIND ANYTHING ELSE THAT COULD HAVE CAUSED THE ENG TO BEHAVE AS IT DID. WE ARE ESPECIALLY GOING TO HAVE HIM EXAMINE THE HEADER FUEL TANK AND THE FUEL LINES TO SEE IF THERE IS ANY FOREIGN MATTER PARTIALLY BLOCKING THE FLOW TO THE CARB. AS OUR ACTIONS; WE FELT AS IF WE DID THE RIGHT THING LNDG WHERE WE DID AND WHEN WE DID. WE COULD HAVE GONE A BIT FARTHER; BUT WE SAW A CLR WAY TO A SAFE LNDG AND WE TOOK IT. NO ONE WAS INJURED AND NO DAMAGE WAS DONE TO PERSONS OR PROPERTY IN THE AIR OR ON THE GND.

Data retrieved from NASA's ASRS site as of January 2009 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.