Accident Details
On July 3, 2013, at approximately 1140 central daylight time, an American Champion Aircraft model 7GCBC, registration N255SF, collided with high vegetation and terrain during a forced landing near Lufkin, Texas. The airplane was registered to and operated by KCSI Aerial Patrol Inc. under 14 Code of Federal Regulations Part 91 as an aerial observation flight. The airline transport rated pilot and his passenger were uninjured. The aircraft sustained substantial damage to its wing struts.
The flight originated from the Texas Gulf Coast Regional Airport (LBX), near Angleton, Texas, about 0945 and was destined for the Angelina County Airport (LFK), near Lufkin, Texas. Day visual flight rules conditions prevailed, and the flight did not operate on a VFR flight plan.
Pilot Actions
According to the pilot's accident report, the airplane was serviced with a full load of fuel at LBX. The purpose of the flight was a working pipeline patrol flown at 500 feet above ground level. Weather was VFR with light to variable wind. After a radio call to area traffic at LFK to state position and intention, the pilot continued the patrol. About six miles south of LFK, an abrupt loss of engine power occurred. The pilot checked fuel tank levels, which were 1/2 tank on the left side and "a little more" than 1/4 tank on the right side. He also checked the mixture setting, carburetor heat, magnetos, throttle position, and the fuel shutoff valve, observing no obvious issues.
The pilot contacted the LFK common traffic advisory frequency, announced the engine trouble, and indicated he would conduct a forced landing about five miles south of LFK. He landed the airplane in a field with high vegetation and reported no fuel or oil leaks as he secured the airplane.
Post-Accident Examination
A Federal Aviation Administration inspector examined the airplane and confirmed the substantial damage. The airplane was recovered, and the operator started the engine after the accident. The operator indicated that when the carburetor was "tapped" after an engine stoppage, the engine would start producing power again.
The carburetor, a Marvel-Schebler MA-4SPA model marked with part no. 10-3678-32, was shipped to the investigator in charge for a tear-down examination. The carburetor's accelerator pump link was manufactured with three holes; the selection of a link hole is model specific. The accelerator pump plunger stem was secured in a link hole that was not specified for the accident carburetor part number. The accelerator pump was operational and ejected a test fluid when the throttle linkage was rotated by hand.
Carburetor Analysis
Disassembly revealed that the carburetor's fuel screens were clear of debris. The carburetor was equipped with a solid blue epoxy float. The needle valve's movement within its seat was restricted. The forked valve clip's forks were observed to rest on the valve seat when the carburetor's throttle body was inverted. The Marvel-Schebler aircraft carburetor maintenance manual describes procedures for overhauling the manufacturer's carburetors and specifies how to determine and adjust the required minimum clearance between the forked valve clip and the valve seat on solid blue epoxy float equipped carburetors.