On November 12, 2000, at 1050 hours mountain standard time, a Cessna 150E, N4031U, came to rest inverted after experiencing a loss of engine power. The pilot made an emergency landing in an open desert area approximately 4 miles southwest of the Marana Northwest Regional Airport, Marana, Arizona. The airplane was operated by the pilot under the provisions of 14 CFR Part 91, and sustained substantial damage. The private pilot and one passenger were not injured. Visual meteorological conditions prevailed for the personal flight and no flight plan had been filed. The flight had departed Ryan Field, Tucson, Arizona, at 1030, and was scheduled to terminate at the Marana airport.

A Safety Board investigator interviewed the pilot; he stated that he and his son had flown to Ryan Field earlier that day for his son's flight lesson. After the son's fight instruction was over he mentioned to his father that while conducting touch-and-go takeoffs and landings the engine was running rough. The son stated that the engine would balk and sputter and cough every time he added full power. The pilot inquired as to the son's method of engaging the throttle and the son indicated that he did not push the throttle in quickly. The pilot asked his son if he had told his flight instructor of the problem and the son replied that he had not. The pilot reported that he had called his son's flight instructor and the instructor told him that during one of the touch-and-go takeoffs the son had engaged the throttle too quickly and the engine sputtered and coughed, but he (the instructor) reduced the throttle. The instructor further stated that there was nothing unusual with the engine during the flight lesson.

After the conversation between the father and son was over they got into the airplane and prepared to depart for home base. No discrepancies were noted with the taxi to the runway or the takeoff roll or initial climb out. Approximately 15 minutes into the flight, at 4,000 feet, he noted a drop in rpm to 1,500 rpm. He stated that when he engaged the throttle the engine would stop, but when he reduced the throttle the engine would run smooth at lower rpm's. The pilot engaged the carburetor heat, but he lost approximately 200 rpm and it made no change in the power output of the engine. He double checked the mixture and noted that it was full rich. He indicated that he does not lean the mixture below 5,000 feet. The pilot reported that he had dropped down to 1,500 feet and was 4 miles from the destination airport when he made the emergency landing. On the landing rollout the airplane struck brush typical of the Arizona desert. The nose wheel collapsed and the airplane came to rest inverted.


An engine examination and test run were conducted at Air Transport in Phoenix, Arizona, on November 28, 2000, under the supervision of a Safety Board investigator. The investigator noted that the wing fuel tank vent line of the left wing was plugged with dirt. The engine remained attached to the airframe. The fuel strainer was damaged and not secure on the firewall. The fuel line from the strainer drain to the carburetor was disconnected at the drain, but connected to the carburetor. The fuel line was found clear of debris. Throttle and mixture cables were operated and full travel was observed at the carburetor.

The top spark plugs were removed and inspected. According to the Champion Aviation Check-A-Plug, AV-27, the spark plugs appeared normal. The rocker box covers were removed and the engine was manually rotated. Thumb compression was obtained in all cylinders in firing order. The valves moved in sequence and appeared uniform. The accessories at the rear of the engine rotated freely. Spark was obtained at the spark plug leads. The spark plugs and rocker box covers were replaced to facilitate an engine run. A fuel supply was connected to the intake line to the carburetor and an auxiliary battery was connected with jumper cables to the airplane's battery.

The first attempt to start the engine was unsuccessful. Ether was sprayed into the intake filter. The engine started and ran about 10 seconds. The procedure was repeated several times; however, the engine would not run for more than 10 seconds. The carburetor was removed and partially disassembled for inspection. Fuel was observed inside the bowl and the floats were unrestricted when manually moved. The main jet appeared free of debris. The carburetor was reassembled and sent out for further examination.

The carburetor was sent to the Federal Aviation Administration (FAA) Flight Standards District Office in Renton, Washington. On January 18, 2001, an FAA Airworthiness inspector took the carburetor to Precision Airmotive in Renton, Washington, for further examination.


The external examination revealed that the throttle lever was safetied per an old Airworthiness Directive, but was the new style, and therefore, did not need to be safetied. The throttle body/bowl was dirty. The manufacturer noted that the bowl screws were a fillister type with no lock wire present. The accelerator pump sump bolts had lock tabs that were installed incorrectly.

The carburetor was flowed in the as received condition. It was noted that when fuel was applied initially it flooded the system. The technician tapped on the side of the carburetor and stopped the flooding. No further discrepancies were noted.


A teardown inspection was conducted on the carburetor after the bench test. The fuel inlet screen was found clear of debris. The technician noted that the gaskets were "ok," but old and hard. Venturi was a one-piece unit. The float valve retractor clip was adjusted too loosely on the float and needle to ensure a positive retraction of the needle. This allowed the clip to stick in the down position, and allowed an increased amount of fuel to enter the carburetor.

The technician also observed that there was rust in the carburetor bowl around the drain plug area. The accelerator pump sump retainer had an excessive amount of "blue silicone sealer" around it and the sump. The accelerator pump discharge check valve was leaking, not sealing properly. He also observed that the accelerator pump plunger spring was rusty and the leather packing was worn.

No further discrepancies were noted.

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