N46492Cessna 172K · 1968

On March 20, 2012, about 1945 eastern daylight time, a Cessna 172K, N46492, experienced a partial loss of engine power during cruise flight near Belfast Municipal Airport (BST), Belfast, Maine. The certificated flight instructor (CFI) and student pilot were not injured during the off airport landing to a road near BST. The airplane sustained substantial damage to the wings and fuselage. The airplane was operated by a local flight school under the provisions of 14 Code of Federal Regulations Part 91 as an instructional cross country flight. Night visual meteorological conditions prevailed and no flight plan had been filed. The flight had departed from the Hancock County - Bar Harbor Airport (BHB), Bar Harbor, Maine about 1910 and was enroute to the Portland International Jetport (PWM), Portland, Maine.

According to written statements provided by the CFI and student pilot, the flight had departed about 1910 and had climbed to 6,500 feet above mean sea level. The engine began to "cough" and the CFI placed the mixture control into the "full rich" position and applied carburetor heat. It was determined that the flight would divert to BST, which was behind them but the closest airport. The CFI took control of the airplane while the student pilot located the frequency and attempted to activate the pilot controlled lighting. However, due to the fact that the runway lights were unable to be activated, they attempted to land on the dark runway utilizing the airport rotating beacon as a reference. The airplane was too far down the runway to make a landing and the CFI executed a go-around maneuver. During the climb out, the engine lost total power and a forced off-airport landing was made. During the landing, the airplane's right wing struck a utility pole, and the right wing and fuselage sustained substantial damage.

A Federal Aviation Administration (FAA) inspector examined the airplane following the accident. The examination revealed that both wings of the airplane was damaged, fuel was leaking from the fuel tanks, the propeller blades had slight curling at the tips, and there was no damage to the engine. A test-run of the engine was conducted; however, with the damage sustained to the propeller, the engine was not operated at full power, but was operated above 1600 rpm, with no abnormal sounds or discrepancies noted. The engine power was reduced to idle and carburetor heat was applied, which resulted in a rise of about 60 rpm. The engine was then shutdown utilizing the mixture control with no anomalies noted. Photographs provided by the FAA inspector revealed that the airplane was equipped with two communication radios identified as "Comm 1" and "Comm 2." The frequency selected in "Comm 1" was associated with Bangor Automated Flight Service Station and the frequency selected in "Comm 2" was associated with BST common traffic advisory frequency (CTAF). The radio selector knob, located on the upper right side of the audio control panel was selected to "Comm 1."

According to information provided from the operator and FAA records, the airplane was manufactured in 1968, and was equipped with a 160-horsepower, Lycoming O-320-E2D reciprocating engine. It was a four-place, all metal, high-wing, single-engine, cantilever monoplane with fixed tricycle landing gear. The most recent 100 hour inspection was conducted on December 6, 2011 and at that time the airframe had 3,926.2 total hours time in service. The engine had 8,054.7 total hours, 256.7 total hours since overhaul, and 18.6 total hours since the most recent inspection.

At 1955, the recorded weather at Knox County Regional Airport (RKD), Rockland Maine, located 21 miles south of the accident site, included wind from 280 degrees at 5 knots, visibility 10 miles, temperature 10 degrees C, dewpoint 6 degrees C.

According to the FAA Special Airworthiness Information Bulletin (SAIB) CE-09-35, based on the recorded temperature and dew point about the time of the accident, the conditions were favorable for serious carburetor icing at cruise power setting.

According to FAA Pilot Handbook of Aeronautical Knowledge (FAA-H-8083-25), Chapter 10 "Weather Theory," states in part "…the average rate of temperature change is 2°C (3.5°F) per 1,000 feet."

FAA Advisory Circular (AC) 20-113 dated October 22, 1981, titled, "Pilot Precautions and Procedures to be Taken in Preventing Aircraft Reciprocating Engine Induction System and Fuel System Icing Problems" stated in part "Induction system icing may be characterized as Impact Ice, Throttle Ice, and Fuel Vaporization Ice. Any one, or a combination of the three kinds of induction icing, can cause a serious loss of power by restricting the flow of the fuel/air mixture to the engine…it is usually preferable to use carburetor heat or alternate air as an ice prevention means, rather than as a deicier… throttle ice is usually formed at or near a partially closed throttle, typical of an off-idle or cruise power setting…visible moisture in the air is not necessary for this type icing…the decline in engine power will probably continue …insufficient power may be available to maintain flight; and complete stoppage may occur, especially if the throttle is moved abruptly…If induction system ice is suspected of causing a power loss, apply full heat or alternate air. Do not disturb the throttle until improvement is noted...The likelihood of icing increases as the temperature decreases (down to 32°F) and as the relative humidity increases."