History of Flight
On July 8, 2023, at 2201 Pacific daylight time, a Cessna C172N, registration N4922G, was substantially damaged during an accident near San Rafael, California. The pilot sustained serious injuries and the passenger received fatal injuries. The flight was conducted as a personal flight under 14 Code of Federal Regulations Part 91.
The airplane had departed San Rafael Airport (CA35) at about 1000 and arrived at Silver Springs Airport (SPZ), Nevada, at 1150. The pilot intended to refuel at SPZ before returning, but airport personnel were not available to operate the fueling equipment. The pilot departed SPZ at about 1900 and flew to Minden-Tahoe Airport (MEV), Nevada, where he purchased 22.63 gallons of 100 Low Lead fuel using a self-service pump.
According to the pilot and ADS-B data, the airplane departed MEV at 2000 and circled while climbing from 4,600 ft mean sea level to about 12,500 ft to clear terrain before proceeding direct to CA35. The pilot remained at altitude as long as possible before beginning a descent about 65 miles northeast of CA35. The airplane maintained 90–110 knots on a heading of about 240° until about 2159. During the remainder of the flight, the airplane slowed and descended, reaching 43 knots at 500 ft at 2200:17. The last ADS-B data at 2200:48 indicated 70 knots at 0 ft about 0.4 miles northeast of the approach end of runway 22 at CA35. The accident site was about 0.2 miles from the runway threshold.
The pilot had limited memory of the accident but recalled the engine did not respond when he advanced the throttle during an attempted level-off. He checked the fuel selector, magnetos, and carburetor heat, but the engine did not respond. He then aimed to maintain best glide speed of 70 knots but could not recall subsequent events. The pilot stated he would not normally select carburetor heat until below 1,500 ft and entering the traffic pattern.
Meteorological Information
The temperature and dew point at the time of the accident were conducive to the formation of serious carburetor icing at cruise power, according to the FAA Special Airworthiness Information Bulletin CE-95-35.
Wreckage and Impact Information
The wreckage was mostly intact, located on the edge of a small waterway about 0.2 miles northeast of the approach end of runway 22 at CA35. It was partially submerged and partially inverted, with the nose pointing east. High-tension power lines about 30 ft tall and 175 ft northeast of the wreckage were broken.
A postaccident examination verified flight control continuity from the cockpit to all surfaces; flaps were found in the UP position. Both wings remained partially attached by control cables, and both fuel tank pick-up lines were separated. The fuel selector valve was in the "Both" position; all valve positions functioned with compressed air, and no fuel was present in the lines. A small amount of blue liquid consistent with fuel and a large amount of water were found in the strainer bowl (the engine was submerged at the scene). A fuel smell was detected when the right tank cap was opened.
Arcing signatures were found on the right wing tip and both wing struts. Powerline cable impact signatures were observed on both wing struts and both sides of the empennage. An undetermined length of approximately 1-inch diameter cable was wrapped around the rudder, both horizontal stabilizers, and the elevator. Both wing struts were severed at their fuselage attachments consistent with cable impact. The carburetor heat selector was found in the ON position. No preimpact airframe anomalies were noted.
Postaccident engine examination revealed no evidence of preimpact mechanical malfunctions or failures. The two-bladed fixed-pitch propeller remained attached; both blades were straight with no chordwise scratches or leading-edge gouges. One blade exhibited witness marks at midspan and arcing signatures consistent with contacting an energized power line, and its tip had a missing corner with arcing signatures.
Additional Information
The FAA Special Airworthiness Information Bulletin CE-09-35 notes that carburetor icing can occur at temperatures above freezing with visible moisture or high humidity due to fuel vaporization and the Venturi effect causing sudden cooling. Carburetor ice is detectable by a drop in rpm in fixed-pitch propeller airplanes. The Pilot's Operating Handbook normal Descent checklist (Step 3) states "Carburetor Heat – AS REQUIRED (to prevent carburetor icing)" and the Before Landing checklist (Step 4) states "Carburetor Heat – ON (apply full heat before closing the throttle)."