Accident Overview
On August 27, 2010, at approximately 1450 eastern daylight time, a Champion Aeronca 7HC, registration N8919R, sustained substantial damage during a forced landing following a loss of engine power near Blue Lick Airport (07KY) in Louisville, Kentucky. The airplane was operated by a private individual as a Title 14 Code of Federal Regulations Part 91 instructional flight. The certified flight instructor and student pilot were not injured. Visual meteorological conditions prevailed.
Aircraft Information
The airplane had undergone a restoration process. The wings were removed for repairs, and new fabric work was completed. The carburetor was overhauled by a Federal Aviation Administration (FAA) approved repair facility and reinstalled in June 2009. The paint job was finished around November 2009, after which the engine was initially started. The engine had accumulated about 2 hours of ground runs prior to the accident.
Flight and Instructor Accounts
The student pilot reported that about three weeks before the accident, he taxied and performed engine ground runs to become familiar with the airplane before starting tail wheel instruction. Earlier on the accident day, the CFI and student flew once in the pattern to assess the airplane's performance, which was described as unremarkable. After landing, they parked, attended ground school, and returned after lunch for flight training. The preflight and ground run up checks were unremarkable. The student was at the controls during takeoff. At an estimated altitude of 800 feet above ground level, while initiating a right bank, a sudden total loss of engine power occurred. The CFI assumed control and chose to land in an open field within a residential area. During the landing, the right wing struck a street stop sign and a phone cable box. Both main landing gear bent and separated aft before the airplane came to a stop.
Post-Accident Examination
An FAA inspector examined the airplane after recovery. The fuel tanks contained about 16 gallons of aviation fuel, and fuel was observed up to the carburetor system. All cylinders had compression, and sparks were noted at the spark plugs during propeller rotation. A post-recovery engine run was performed; the engine started and produced power. The carburetor was then removed and partially disassembled. One of the floats exhibited a noticeable hole at its lowest point. The carburetor was sent to the National Transportation Safety Board Materials Laboratory for metallurgical examination.
The perforation measured 0.14 inch in length and 0.09 inch in width. The area around the perforation showed surface features such as pits and roughening, consistent with a chemical etching reaction similar to corrosion. The location of the perforation and surrounding etched areas suggested that a small quantity of liquid corrosive to brass remained in the bottom of the carburetor bowl for sufficient time for the chemical reaction to occur. The corrosion progressed to the point of disintegrating the float's skin, creating the perforation. Review of the carburetor overhaul documentation indicated that the float was reused and was not required to be replaced at that time. The overhaul facility returns newly overhauled carburetors dry, without any preservative treatment.