Accident Overview
On January 26, 2014, at 1717 central standard time, a Cessna 172K, registration N4VN, sustained a total loss of engine power when the pilot applied carburetor heat during a visual approach to Quad City International Airport (MLI) in Moline, Illinois. The pilot executed a forced landing to a field near Milan, Illinois. The right wing of the airplane was substantially damaged. The commercial pilot and a passenger were not injured. Visual meteorological conditions prevailed at the time. The flight, operated under 14 CFR Part 91 as a personal flight, was not on a flight plan. It departed Davenport Municipal Airport, Davenport, Iowa, at 1615 and was destined for MLI.
Sequence of Events
The pilot reported that after receiving a landing clearance for runway 31 from the MLI air traffic control tower, following a special visual flight rules clearance, he applied carburetor heat about one mile from the runway. Immediately, the engine ceased operating. He performed a forced landing to a field, touching down at approximately 10-15 mph. The pilot noted that during the pre-departure engine run-up, there was a decrease in engine rpm when he checked the carburetor heat operation.
Aircraft and Carburetor Information
The aircraft was a Cessna 172K equipped with a Marvel Schebler MA-4-5 carburetor, part number 10-3676, serial number MS820601. Logbook entries indicated an annual inspection on June 25, 2013, at a tachometer reading of 4,571 hours, and a carburetor replacement with an overhauled unit on October 21, 2013, at 4,626 hours. The tachometer at the time of the accident was 4,669 hours. The owner stated that the mechanic who performed the last annual inspection also installed the carburetor and subsequently removed it for post-accident examination. No mechanical anomalies were found in the carburetor heat system during removal.
Meteorological Conditions
The Automated Surface Observing System at MLI recorded at 1715: wind from 340 degrees at 11 knots, gusting to 21 knots; visibility 1 statute mile; runway visual range for runway 9 was 6,000 feet; light frozen precipitation; broken clouds at 2,700 feet and 4,000 feet, overcast at 4,900 feet; temperature -1°C; dew point -5°C; altimeter 29.55 inches of mercury. The pilot stated the airplane did not enter any snow showers approaching MLI, reporting that the snow showers arrived about 30 minutes after the accident.
Post-Accident Examination
The Federal Aviation Administration's DuPage Flight Standard District Office did not dispatch an inspector to the accident site. The National Transportation Safety Board Investigator-In-Charge requested the owner provide the carburetor and maintenance logbook copies, which were supplied. A post-accident disassembly examination, overseen by the IIC and an FAA inspector, revealed that the fuel screen contained no contaminant, the idle screw was extended about 2-1/2 turns, and the throttle valve and float clearances were within service manual specifications. All carburetor retaining hardware was in place and secure.
Carburetor Icing Probability
Special Airworthiness Bulletin CE-09-35, Carburetor Icing Prevention, includes a graph indicating the probability of carburetor icing for given temperature and relative humidity conditions. At the recorded temperature and dew point, the graph showed a probability of icing at glide and cruise power settings.