NTSB Factual Report

On February 23, 2002, at 1825 eastern standard time, a Cessna 170, N3832V, was substantially damaged during a forced landing on approach to runway 24 at Shannon Airport (EZF), Fredericksburg, Virginia. The certificated commercial pilot was seriously injured. Visual meteorological conditions prevailed for the flight that originated at Fredericksburg, about 1645. No flight plan was filed for the local personal flight, conducted under 14 CFR Part 91.

During a telephone interview, the pilot stated that the purpose of the flight was to calibrate his airspeed indicator. He flew the airplane for about 1 hour and 40 minutes with no deficiencies noted in its performance or handling. He flew at a constant altitude, at various power settings and airspeeds, to collect data for the calibration. Once the data collection was completed, he returned to his home airport.

The pilot entered the traffic pattern for runway 24, and extended the downwind leg for spacing. He slowed the airplane to 90 miles per hour (mph), and applied carburetor heat. During the remainder of the approach, he made incremental reductions in power and airspeed, and corresponding increases in flap settings.

When he turned onto the final approach course and reduced the throttle to idle, the engine stopped producing power. The pilot said he confirmed the throttle, mixture, and carburetor heat settings, and felt he had the runway "made". He said that because he was below 500 feet, he chose not to attempt a restart. About 200 feet further into his descent, the pilot realized that he couldn't reach the runway. He reviewed his forced landing options, and chose to land on the railroad bed to his front. Just before touchdown, the pilot "flared really hard, and pancaked [the airplane] into the embankment."

The airplane came to rest on the rail bed, about 75 feet from the approach end of runway 24.

The airplane was examined at the site on February 24 and 26, 2002, by two Federal Aviation Administration (FAA) inspectors. At the completion of the examination, one inspector was interviewed by telephone, and the other submitted a written statement of their findings.

During the telephone interview, the inspector stated that fuel was noted in both fuel tanks, and fuel system integrity was confirmed. Fuel samples were taken, with no water or contaminants noted. The propeller was rotated by hand, and engine continuity was established. Both magnetos "snapped", and spark was produced at each spark plug. Thumb compression was confirmed on all cylinders, and the engine-driven fuel pump was operational.

According to a written statement by the FAA inspector (airworthiness), the main fuel screen in the carburetor was not properly torqued, and there was evidence of an old fuel leak at the fuel screen fitting and along the parting surfaces of the carburetor. The carburetor heat scat hose was found ripped length-wise, with the internal core unraveled, and disconnected form the carburetor air box.

The carburetor air box was found slightly damaged. The carburetor heat control had been cut when the engine was removed during the recovery process. The air valve control arm was not free to move, even with the cut cable. It was noted that a repair had been previously made to the airbox control arm. The repair/modification consisted of two strips of sheet metal, about 2 inches long, and riveted together. One end of the bonded strips was attached to the control arm with a nut and bolt, and the other end had the carburetor heat cable attached to it via a drilled bolt.

The cable was kinked approximately 1.5 inches from where it was attached to the strip of metal. According to the inspector, this arrangement was an alteration/modification to the carburetor heat control system.

The pilot held a commercial pilot certificate with ratings for airplane single engine land and instrument airplane. He also held a flight instructor certificate with ratings for airplane single engine land.

The pilot's most recent FAA second-class medical certificate was issued March 22, 2000. The pilot reported 407 hours of total flight experience, 93 hours of which were in the Cessna 170.

The airplane was a 1948 Cessna 170. The pilot said he purchased it on December 30, 2000. He also said the most recent annual inspection was completed on July 20, 2001, and the inspection required 3 days to complete.

The pilot further stated that he was present for the inspection, and that there were no significant anomalies noted or repairs performed. The pilot was asked if any repairs or modifications had been performed on the carburetor heat box or carburetor heat controls since he had owned the airplane, and he said no. He also said that during the inspection, operation of the air valve was confirmed visually, and that actuation of the carburetor heat control during engine operation resulted in a 300-rpm drop.

The pilot was also asked if, during the annual inspection, he was advised of any deficiencies that might need attention prior to the next inspection. The pilot said no. According to the pilot:

"The only thing the mechanic told me was that I might need new fabric on the wings in a year or two. He showed me a couple of spots through the inspection panels, but the [inspection authority] wasn't as concerned as the mechanic."

The weather reported at Fredericksburg, at 1821, included clear skies with the wind from 070 degrees at 3 knots. The temperature was 45 degrees Fahrenheit and the dewpoint was 21 degrees Fahrenheit. According to an FAA Carburetor Icing Probability Chart, the atmospheric conditions were conducive to icing at glide and cruise power settings.

NTSB Probable Cause

The unauthorized modification of the air control box by unknown persons, and the failure of subsequent mechanics to note and correct the deficiency. Factors included the carburetor icing conditions and the unsuitable terrain mandated by the forced landing.