N5208FCessna 172F · 1965

On January 19, 2013, about 1605 Pacific standard time, a Cessna 172F, N5208F, made a forced landing into a muddy field following a total loss of engine power during the initial climb from the Yuba County Airport, Marysville, California. Beale Aero Club was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The certified flight instructor (CFI) and passenger sustained minor injuries; the airplane sustained substantial damage. The local positioning flight departed from Beale Air Force Base, Marysville, California at 1553 with a planned destination of Yuba County Airport. Visual meteorological conditions prevailed and a military visual flight rules (VFR) flight plan had been filed.

The CFI stated that the airplane had recently undergone an annual inspection and this flight was the first since that maintenance was performed. The CFI intended to reposition the airplane at the Yuba County Airport where it was normally based. After departure, he made the approximate 6 nautical mile flight to the destination, at which point he decided to perform several touch-and-go practice takeoff and landings. Following a smooth landing, he configured the airplane for takeoff by confirming the fuel selector was positioned on "BOTH" wing tanks, the carburetor heat was off, the flaps were retracted, and the fuel mixture was "RICH." He applied full power and the airplane climbed about 150 feet, during which time he noted the oil pressure and temperature were showing normal indications.

Shortly thereafter, the engine suddenly experienced a total loss of power. He lowered the nose and configured the airplane for its best-glide airspeed. Despite his efforts, the CFI could not restart the engine and the airplane touched down in a muddy field. The main landing gear dug into the soft terrain and the airplane flipped over coming to rest inverted. The wreckage was located about 50 feet from the first impact location and about 0.5 miles from the edge of the runway.

The Cessna 172F, serial number 17253209, was manufactured in 1965. The engine's data plate indicated it was a Teledyne Continental Motors O-300-D engine, serial number 25471-D-73-D-R.

Fuel System Design

The airplane's fuel system was a gravity-fed design where fuel flowed from metal tanks in the inboard section of each wing, through a selector valve, and continued to a fuel strainer before entering the carburetor.

The fuel selector valve was located near the floor of the fuselage between the pilot and copilot positions on the pedestal. The valve was coupled to a selector handle via a diagonally affixed shaft. The handle positions were labeled "OFF, LEFT, BOTH and RIGHT" with a placard. The handle could be rotated either direction, and was designed to settle into a detent located at one of four selected positions. Upon rotation of the handle, a cam lobe in the fuel valve applied pressure against a series of spring-loaded ball-bearing valve fittings. Depending on the position of the cam, fuel could pass through either the left or right tank fitting, or no fuel would be ported to the fitting that was routed to the carburetor.

The selector handle was designed to be affixed to its shaft via an offset spring-pin that slides through a hole on the handle and shaft when properly aligned (will only fit in one direction to prevent the handle from being installed incorrectly).

Maintenance

A review of the airplane maintenance logbooks revealed that the engine had accumulated 5,038.1 hours total time, and 1,563.1 hours since the last major overhaul. The last annual inspection was dated as having been completed January 18, 2013. The records indicated that during this maintenance the mechanic complied with Cessna Service Bulletin SB99-18R1A, which requires draining the fuel tanks to inspect the fuel gauge accuracy.

The mechanic that worked on the airplane was the director of maintenance, and maintained all of the operators' airplanes, which was a flight club that also provided training. He stated that the airplane's last annual inspection took longer to perform than was usual because he had been interrupted to do a 100 hour inspection for another airplane. He recalled that he had received the accident airplane for maintenance on October 31, 2012 with minimum fuel (since he had to check the fuel quantity indicator), and January 19 was when he returned the airplane back into service.

The mechanic further stated that his normal fuel system check during an annual inspection was as follows: Upon receiving and then releasing the airplane back into service, he would turn the selector to the "OFF" position and observe the amount of time the engine continues to run. This procedure would aid him in ensuring that the selector was shutting off the fuel and that the seals were intact. He would then test all the fuel selector positions. Subsequently, as part of the annual, he would remove the center console and the fuel selector cover in an effort to complete the checklist required item of cycling the selector and looking for leaks. He has had experiences in the past where he has seen selectors leaking or where the engine doesn't completely shut off.

The mechanic recalled that he had taken the selector handle off in an effort to remove the panel. He then checked to make sure the detents engaged into each position selected. If the shaft's alignment was slightly off it wouldn't feed from the correct tank, which he would be able to see from staining around the valve. The handle is usually indexed so that it can only be installed in the correct position. This is accomplished by an offset roll-pin that can only be inserted with proper alignment, but in the accident airplane, the handles offset hole had been drilled out to accommodate a bolt, which in turn enabled the handle to be able to be secured 180-degrees out of alignment. He was sure he had it in the correct position because during the post-inspection he put the selector in the both position and the engine ran normally. He ran the engine in the "LEFT," "RIGHT," and "BOTH" positions, though he didn't test "OFF"). He did check the "OFF" position when receiving the airplane, but did not do it after finishing the annual.

The engine and fuel system were examined following recovery of the wreckage; a detailed examination report with pictures is appended to the report in the public docket.

An external examination of the engine case revealed that it was intact with no holes or perforations observed. Investigators rotated the engine via the propeller. The engine's internal mechanical continuity was established during rotation of the crankshaft and upon attainment of thumb compression in all cylinders. Visual inspection of the engine revealed no evidence of foreign object damage or detonation, and no indication of excessive oil consumption. The valve train was observed to operate in proper order and equal lift action occurred at each rocker assembly. An oil film was present in the all six rocker box areas. The left magneto, Slick model 6364, serial number 04091034 was removed and function tested. The test revealed that the magneto did not produce adequate spark. The magneto was dissembled for further evaluation. It was determined the cam was worn causing the point gap to be out of the manufacture's tolerance.

The airplane had sustained damage to the wings during the accident sequence, however the fuel tanks appeared to be intact and no ruptures could be located. The fuel selector handle was positioned on the "RIGHT" selection, consistent with the pilot's statement of where it was at the time of the accident. The hardware attaching the handle to the shaft consisted of a bolt with a washer and nut securing it, rather than the spring-pin listed in the Cessna Illustrated Parts Catalogue. The handle appeared to have a smaller hole (slanted diagonal) machined below the larger hole that the bolt attached through.

Investigators disconnected the carburetor and noted that with the fuel selector handle near the "OFF" position (just left of the detent), the fuel flowed freely through the valve. When the selector was positioned in the "BOTH" position the fuel stopped flowing, consistent with handle indicating an opposite selection.

Removal of the pedestal revealed that the fuel selector assembly and valve rotated when the handle was turned. Disassembly of the fuel valve disclosed that all four detent positions on the cover were worn and contained debris; the cam lobe appeared worn.