NTSB Factual Report

On April 14, 2005, approximately 1230 central daylight time, a Cessna 172N single-engine airplane, N733UV, was substantially damaged during a forced landing following a reported loss of engine power while maneuvering near Olney, Texas. The commercial pilot, sole occupant of the airplane, sustained minor injuries. The airplane was registered to and operated by LH Underwood and Son Aerial Patrol, of Guthrie, Oklahoma. No flight plan was filed for the cross-country flight that originated from the Wichita Valley Airport (F14), near Iowa Park, Texas, at 1140. Visual meteorological conditions prevailed for the aerial observation flight conducted under 14 Code of Federal Regulations Part 91.

The 833.9-hour pilot reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that while flying a pipeline patrol mission, he noticed that the throttle had backed-out and he pushed it full to the forward position. As the airspeed decayed, he applied carburetor heat and noticed the engine was not running rough. The pilot pushed the carburetor heat back in, and noted that the engine was still losing power. At an altitude of approximately 200 feet above ground level, the pilot initiated a forced landing to a nearby field. During the landing roll, the nose gear dug into soft terrain and the airplane nosed over.

The airplane was examined at the accident site by a Federal Aviation Administration (FAA) inspector. According to the inspector, the airplane came to rest inverted within an open field. The nose gear was separated and the engine firewall was bent. The left wing, vertical stabilizer, and rudder were structurally damaged. Fuel was observed leaking from both fuel caps. During the recovery of the airplane, fuel was observed in both fuel tanks.

Examination of the Lycoming O-360-A1A engine, serial number L-30219-36A, was conducted by an FAA inspector on April 20, 2005. The engine was rotated by hand using the propeller, and valve train continuity and compression were established on each cylinder. When compared to the Champion Aviation Check-A-Plug Wear Guide (Part Number AV-27), the cylinder #1, 2, 3, 4 top spark plugs displayed signatures consistent to normal operation. No anomalies were noted during the engine examination.

Review of the airplane maintenance logbooks revealed that the airplane underwent an annual inspection on January 2, 2005, at an airframe total time of 15,293.3-hours, and an engine total time since major overhaul of 2,568.4-hours. At the time of the accident, the airframe and engine had accumulated 62.3 hours since the most recent annual inspection.

The automated weather observing system (AWOS) at the Graham Municipal Airport (RPH), near Graham, Texas, located approximately 16 miles southeast of the accident reported at 1206 reported wind from 060 degrees at 3 knots, visibility 10 statute miles, clear sky, temperature 68 degrees Fahrenheit, dew point 45 degrees Fahrenheit, and an altimeter setting of 30.18 inches of Mercury.

A review of the information found on a Carburetor Icing Probability Chart, given the atmospheric conditions prevailing during the flight, revealed that the airplane was operating within the "moderate icing - cruise power or serious icing - glide power" range.

NTSB Probable Cause

The loss of engine power due to carburetor ice. Contributing factors were the weather conditions conducive for carburetor icing and the lack of suitable terrain for a forced landing.