On October 27, 2018, about 0915 central daylight time, a Cessna 172 G airplane, N3973L, impacted a creek near Houston, Texas, during a forced landing following a loss of engine power. The commercial pilot and two passengers were uninjured. The airplane sustained substantial wing damage during the forced landing. The airplane was registered to IFR Flyers LLC and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Day visual meteorological conditions prevailed in the area about the time of the accident, and the flight was not operated on a flight plan. The local flight originated from the West Houston Airport (IWS), near Houston, Texas.According to the pilot's accident report, the purpose of the flight was an orientation flight for two Young Eagles passengers. After departing from runway 15, the pilot followed interstate highway 10 to highway 99, and then flew north about 5 miles. He then flew east and entered a final for runway 15. On short final the pilot added power, but the engine did not respond. He checked the fuel valve, mixture, and engaged the starter with no engine response. He stated, "I saw the aircraft was headed directly to the concrete revetment on the south bank of Bear Creek. I banked the aircraft left, striking the water nose down and with a left bank."
A representative of the recovery company forwarded pictures of the airplane during recovery. The fuel selector was positioned on the both position and the throttle, mixture, and carburetor heat controls were in their forward positions.
A National Transportation Safety Board investigator and a technical representative from the engine manufacturer examined the wreckage at a salvage yard. The airplane was at the salvage yard for several weeks before the examination.
The engine oil dip stick was removed, and water flowed from the dip stick tube. A visual inspection of the motor was conducted, other than evidence of water submersion, no obvious abnormalities were noted. The engine was not free to rotate. However, after removing water from the cylinders, the engine rotated freely. The sound of the magneto impulse couplings were noted. The engine oil was drained from the sump and appeared to be a mixture of oil and water. The removed sparkplugs appeared wet from water. A thumb compression test was completed on each cylinder; suction and compression were present on each cylinder. Each cylinder was inspected via borescope and no preimpact abnormalities were observed. Both left and right magnetos, and the carburetor were removed from the engine. The magnetos were rotated by an impact driver; spark was observed on each terminal, for both magnetos. The carburetor finger screen was not contaminated. The carburetor bowl contained a dirty-brown liquid and when tested with water-detecting pasted; tested positive for water. A small amount of liquid, consistent with aviation fuel, was present in the accelerator pump section of the carburetor.
No preimpact mechanical anomalies were found during the engine examination.
At 0915, the recorded weather at the Houston Executive Airport, near Houston, Texas, was: Wind calm; visibility 10 statute miles; sky condition clear; temperature 18° C; dew point 16° C; altimeter 30.10 inches of mercury.
At 0853, the recorded weather at the David Wayne Hooks Memorial Airport, near Houston, Texas, was: Wind calm; visibility 9 statute miles; sky condition clear; temperature 15° C; dew point 15° C; altimeter 30.08 inches of mercury.
At 0853, the recorded weather at the Sugar Land Regional Airport, near Houston, Texas, was: Wind calm; visibility 10 statute miles; sky condition clear; temperature 16° C; dew point 14° C; altimeter 30.08 inches of mercury.
The recorded local temperature and dew point data near the time of the engine power loss was plotted on a carburetor icing chart. The charted data showed that the weather in the area was conducive to serious icing at any power to moderate icing at cruise power/serious icing at descent power.
The Pilot's Handbook of Aeronautical Knowledge, in part, states:
When conditions are conducive to carburetor icing during flight, periodic checks should be made to detect its presence. If detected, full carburetor heat should be applied immediately, and it should be left in the ON position until you are certain that all the ice has been removed. If ice is present, applying partial heat or leaving heat on for an insufficient time might aggravate the situation. In extreme cases of carburetor icing, even after the ice has been removed, full carburetor heat should be used to prevent further ice formation. A carburetor temperature gauge, if installed, is very useful in determining when to use carburetor heat.