On June 9, 2000, about 1120 Eastern Daylight Time, a Cessna 172R, N7274D, was substantially damaged during a forced landing at the Greenwood Lake Airport (4N1), West Milford, New Jersey. The certificated flight instructor (CFI) and a commercial pilot sustained minor injuries. Visual meteorological conditions prevailed and no flight plan had been filed for the flight that originated from the Westchester County Airport (HPN), White Plains, New York. The instructional flight was conducted under 14 CFR Part 91.

According to the CFI, after a normal pre-flight inspection and pre-takeoff engine check, they departed HPN, to practice some landings at nearby airports. The commercial pilot was flying, and both pilots described the flight to 4N1 as uneventful. When they arrived over 4N1, the commercial pilot entered the "left downwind" for Runway 24. While turning onto the "base leg," at a power setting of 1,900 rpm, about 800 to 900 feet above ground level, he attempted to increase engine power by moving the throttle forward; however, there was no response from the engine. He then told the CFI "there's no power." The CFI assumed control of the airplane, confirmed that the throttle was unresponsive, and noticed that the engine rpm was slowly dropping. The CFI stated she checked that the fuel selector was on "both", the fuel shut off valve was "in", the mixture control was "rich", turned the fuel pump "on," set the throttle to 1/4 inch open, and attempted to restart the engine, without success. She performed a forced landing to trees, which were located about 1/4 mile from the runway.

Both pilots stated they were wearing headsets, and they did not hear any unusual noises or power changes prior to the loss of engine power. Additionally, they reported the airplane's mixture control was not manipulated and remained in the full rich position for the entire flight.

The CFI reported 400 hours of total flight experience, with about 20 hours in make and model.

The commercial pilot reported he had accumulated over 3,600 hours of flight experience, which included about 100 hours in make and model.

Initial examination of the wreckage was performed at the accident site by a Federal Aviation Administration (FAA) inspector. The inspector stated he checked the fuel in the airplane's fuel strainer, which was blue in color and absent of contamination. He also removed two spark plugs from the engine, which were unremarkable, and checked that the air filter was unobstructed.

A FAA inspector, and representatives from Cessna Aircraft and Textron Lycoming, performed an examination of the airframe and engine on June 13, 2000. Prior to their examination, airport personnel without supervision, performed an unauthorized engine test-run without a propeller installed on the engine. The engine was later started and test-run with a propeller installed under FAA supervision and no discrepancies were noted. On June 20, 2000, the wreckage was re-examined under the supervision of a Safety Board investigator, and no evidence of any pre-accident failures or malfunctions were observed. The engine was retained for further examination.

The airplane had been operated for about 390 hours since new. It was maintained under an approved manufacturer inspection program, and was inspected the day prior to the accident. According to maintenance records, the accident engine was manufactured on February 23, 1999, and installed in the accident airplane on April 14, 1999.

On July 6, 2000, the engine was test run at Textron Lycoming, Williamsport, Pennsylvania, under the supervision of the Safety Board investigator. Prior to the test-run, a significant amount of carbon build-up was observed in all cylinder exhaust ports. The engine exhaust system from the accident airplane was not shipped for testing, and subsequently not installed for the test run. The engine started without any hesitation, and several engine parameters were monitored at different rates of airflow. The test run revealed a rich mixture operation in the idle and 400 pound airflow ranges, and a "magneto drop" of 145 and 150 rpm. The idle fuel flow was observed at 11 lbs/hr and the idle mixture leaning rise was 120 rpm. The test run specification required the fuel flow at idle to be between 4 and 6 lbs/hr. In addition, the leaning rpm rise should have been between 10 and 20 rpm. The 400-airflow fuel flow was observed at 44 lbs/hr. The 400-airflow test specification required the fuel flow to be between 33.5 and 40 lbs/hr. In addition, after the engine was leaned, the magneto drop was observed at 120 and 125 rpm. It was noted that despite the rich mixture indications observed during testing, at no time was a loss of engine power experienced.

On August 29, 2000, the engine was test run after installation of the exhaust system from the accident airplane. A FAA inspector supervised the test run. The results of the test run were consistent with the results obtained from the test run performed on July 6.

Review of the engine's production test log, that was perform on February 21, 1999, revealed all fuel flow readings were within their respective test specification ranges.

The fuel injector servo, flow divider, fuel nozzles and lines, were retained for further testing at Precision Airmotive Corporation, Marysville, Washington. The tests were conducted under the supervision of an FAA inspector. The flow divider and nozzles met new production test specifications and exhibited no unusual characteristics. Examinations of the fuel servo did not reveal any physical malfunctions; however, a flow check of the fuel servo revealed a mixture that exceeded the rich test specification limits during several test points.

Review of FAA service difficulty reports (SDR's) revealed that a flight school which operated 53 Cessna 172R model aircraft filed several SDR's between May and August 1999, detailing "numerous unexplained power losses" in their fleet of 172R model airplanes; subsequently the fleet was temporarily grounded. According to the director of maintenance (DOM) for the flight school, after the airplanes were grounded, the school began to upgrade their fleet to 180 horsepower, 172S models. The flight school also implemented several changes to their operating procedures, which included, leaning the fuel mixture and "clearing" the engine during periods of long ground operations. At the time of this report, the DOM stated the school had experienced "almost no problems at all" with their Cessna 172 airplanes.

The Cessna 172R was manufactured with a Lycoming IO-360-L2A engine, which produced 160 brake horsepower at 2,400 rpm. According to Cessna Aircraft, the process of converting a Cessna 172R, to a 180 brake horsepower Cessna 172S, included, but was not limited to, changing the propeller, oil cooler, engine baffling, tachometer, and airspeed indicator. Additionally, the S model airplane utilized a different pilot-operating handbook (POH).

On August 13, 1999, Textron Lycoming issued Service Instruction (SI) N0. 1497, for the IO-360-L2A engine installed in Cessna 172R aircraft, which stated in part: "Flight training operations often present an environment that makes an engine more susceptible to spark plug fouling, reduced efficiency, and excessive fuel consumption. Some of the flight training profiles that cause these conditions are over priming, prolonged idling and taxing at low engine speeds, and extended operation at full rich mixture." The service instruction provided guidance for leaning the engine fuel mixture during ground and flight operations. The information contained in the SI constituted an expansion of Cessna's published operating procedures for the airplane.

On August 18, 1999, Textron Lycoming issued SI N0. 1498, for the IO-360-L2A engine installed in Cessna 172R aircraft, which stated in part: "The fuel system is more susceptible to vapor formation and its effects during operation in warm weather." The SI provided a list of symptoms, which indicated the presence of vapor in the fuel system and the corrective action to use to purge vapor from the system. The time of compliance was as required during aircraft operations. Additionally, the service instruction included the note, "When the engine is operated above 1800 rpm, fuel flow is increased and fuel temperatures throughout the fuel system are greatly reduced. The increased flow purges any vapor and the cool fuel stops vapor from forming." The information contained in the SI constituted an expansion of Cessna's published operating procedures for the airplane.

On December 19, 2000, Textron Lycoming issued SI N0. 1502A, for the IO-360-L2A engine installed in Cessna 172R aircraft which stated in part: " To reduced the possibility of vapor related problems in aircraft employing IO-360-L2A model engines, the flow divider should be modified into an inverted flow divider." The time of compliance was "whenever the engine has vapor related problems, or at owner's discretion." The inverted flow divider became the standard configuration for newly manufactured engines.

On March 5, 2001, Cessna Aircraft issued a Service Bulletin, which modified the 172R and S model airplane's "Before Takeoff" checklist to include, "Throttle - CHECK IDLE." The service bulletin included a note, which stated in part: "If engine roughness occurs at idle, taxi and/or at full throttle with the mixture control in the full rich position, refer to and accomplish the POH Section 4 Fuel Vapor Procedures. If after accomplishing these procedures the engine is still operating rough, then maintenance action is required...."

According to the accident airplane's maintenance manual, the airplane was equipped with a wet wing fuel storage system. The system consisted of an integral fuel tank in each wing, a three-position selector valve, a fuel reservoir tank, an electrically driven auxiliary fuel pump, a fuel shutoff valve and a fuel strainer. The airplane was equipped with 13 drain valves; five drain valves were located for each wing tank, and one drain valve each was provided for the selector valve, fuel reservoir, and fuel strainer.

Examination of the accident airplane's fuel tanks, fuel selector, fuel strainer, fuel servo, flow divider, and injectors did not reveal any evidence of fuel contamination. An estimated 20 milliliters of water was observed in the fuel reservoir. It was noted that the fuel line, which fed directly to the fuel reservoir had been compromised, and the airplane remained outdoors until June 11.

According to a Cessna Aircraft representative, while the airplane was on level ground, the fuel reservoir tank design and construction allowed for up to an estimated 50 milliliters of liquid contamination that could be separated from the fuel in the reservoir and prevented from feeding further in the aircraft fuel system.

The weather reported at an airport about 18 miles south of the accident site, at 1153 was: Winds from 240 degrees at 8 knots; Visibility 8 miles; Sky clear; Temperature 82 degrees F; Dewpoint 61 degrees F, Altimeter 30.00.

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