Springfield, TN, USA
N35571
CESSNA 172I
The pilot was flying the airplane on the second leg of a visual flight rules cross-country trip, which he flew at an altitude of 3,500 feet in order to remain below an overcast ceiling. Approaching the destination airport, the pilot began a cruise descent and, about 10 miles from the airport, began configuring the airplane for landing. The pilot reduced engine power to about 1,500 rpm, set the mixture to full rich, but did not activate the carburetor heat. The engine then lost power, and the pilot subsequently performed a forced landing to a field. During the landing, the nose landing gear struck a ditch. Responders noted that fuel was recovered from the airplane following the accident; the engine was run after the accident with no anomalies noted. The temperature and dew point reported on the surface at an airport located about 21 nautical miles from the accident site were conducive to carburetor icing at both glide and cruise power settings.
On January 19, 2012, about 1455 central standard time, a Cessna 172I, N35571, was substantially damaged during a forced landing near Springfield, Tennessee. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which originated from Vermilion Regional Airport (DNV), Danville, Illinois about 1215, and was destined for John C. Tune Airport (JWN), Nashville, Tennessee. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.According to a written statement submitted by the pilot, he departed from Wittman Regional Airport (OSH), Oshkosh, Wisconsin and stopped at DNV to service the airplane with fuel. After departing from DNV, the pilot climbed the airplane to 3,500 feet in order to remain below a low ceiling of clouds. Several miles north of Springfield, Tennessee, the pilot listened to the JWN automated weather observation and began a cruise descent. About 10 nautical miles north of JWN, and while descending through 2,100 feet, the pilot began to configure the airplane for landing. The pilot reduced engine power to about 1,500 rpm and set the fuel mixture to full rich, but did not activate the carburetor heat. The engine then "suddenly acted as though it were starved for fuel." With rising terrain ahead, and only being about 800 feet above the ground, the pilot "pumped" the throttle, began searching for a suitable forced landing area, and activated the emergency locator transmitter. As the pilot approached the intended landing field from the east, he realized that the airplane was high and fast, so flew north and circled back in order to set up for a landing to the southwest. The pilot subsequently landed the airplane on the downward slope of the field at an airspeed around 60 knots. During the rollout, the nose landing gear struck a ditch and the airplane nosed over. A Federal Aviation Administration (FAA) inspector examined the wreckage following the accident and reported that the airplane had incurred substantial damage during the accident, including damage to the nose landing gear and firewall. The inspector also noted that when he arrived at the accident scene, about 1.5 hours after the accident occurred, a strong odor of aviation gasoline was present. First responders reported recovering about 5 gallons of fuel that had drained from the airplane, and a local airframe and powerplant mechanic who prepared the airplane for recovery by removing the wings from the fuselage reported that each wing contained an "ample" quantity of fuel. The mechanic also noted normal function of the gascolator and the presence of fuel within it. After being recovered from the accident scene, the airplane was examined under the supervision of an NTSB investigator. About 2 ounces of fuel were drained from the carburetor drain plug. Since the wings of the airplane had been removed to facilitate transport following the accident, an alternate fuel source was plumbed to the fuel line fitting at the right wing root. The right fuel tank was subsequently selected in the cockpit, and fuel flowed to the gascolator and carburetor. During a test run, the engine started immediately and without hesitation. The engine was then operated at various power settings between idle and 2,500 rpm for about 5 minutes, with no anomalies noted. The weather conditions reported at Nashville International Airport (BNA), Nashville, Tennessee, elevation 599 feet, located about 21 nautical miles southeast of the accident site, at 1453, included winds from 200 degrees at 10 knots, 10 statute miles visibility, few clouds at 15,000 feet, scattered clouds at 25,000 feet, temperature 10 degrees Celsius (C), dewpoint minus 04 degrees C, and an altimeter setting of 29.97 inches of mercury. According to FAA Special Airworthiness Information Bulletin (SAIB) CE-09-35, Carburetor Icing Prevention, dated June 30, 2009, "Pilots should be aware that carburetor icing doesn't just occur in freezing conditions, it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Icing can occur in the carburetor at temperatures above freezing because vaporization of fuel, combined with the expansion of air as it flows through the carburetor, (Venturi Effect) causes sudden cooling, sometimes by a significant amount within a fraction of a second." The SAIB provided a diagram which showed the probability of carburetor icing for various temperature and relative humidity conditions. Applying the surface temperature and dewpoint reported at BNA about the time of the accident to the diagram showed that "Icing (glide and cruise power)" conditions prevailed. Among the recommendations in the SAIB to pilots was that pilots should, "Use carburetor heat on approach and descent when operating at low power settings, or in conditions where carburetor icing is probable."
The pilot did not apply carburetor heat during approach to landing, which resulted in a total loss of engine power due to carburetor icing.
Source: NTSB Aviation Accident Database
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