HISTORY OF FLIGHTOn December 18, 2020, at 1322 eastern standard time, a Piper PA-28-140 airplane, N6978W, was destroyed when it was involved in an accident near Tampa, Florida. The flight instructor, student pilot, and passenger (the airplane owner) were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The airplane departed Tampa International Airport (TPA), Tampa, Florida, about 0900 for Zephyrhills Municipal Airport (ZPH), Zephyrhills, Florida. Before departing ZPH to return to TPA, the airplane was fully fueled. The airplane departed ZPH about 1307 with the student pilot in the left seat at the controls. The flight instructor stated that the engine was running smoothly during the flight to TPA. The flight instructor stated that he taught the student pilot to accomplish the following items when commencing an approach: fuel pump on, carburetor heat in, mixture rich, flaps set to 10°, and throttle 1,700 rpm, all of which the student had accomplished on the approach to TPA. Review of TPA air traffic control communications revealed that the flight was cleared to land on runway 1R. The passenger, who was seated in the back seat and was videotaping the approach, noted that the student pilot adjusted his seat during final approach, which made the video camera “wiggle.” Moments later, the flight instructor noticed that the airplane’s descent path was starting to get low and advised the student pilot to add power. The student pilot attempted to add power, but the engine did not respond. The flight instructor assumed control of the airplane, established best glide speed, and attempted to restore engine power. The flight instructor noted a momentary increase of 200 rpm when he cycled the throttle, but he was unable to restore engine power with the engine “basically at idle.” The flight instructor contacted air traffic control and stated, “78W, we’re declaring an emergency. We’ve got an engine failure. We’re gonna try and make it.” When the flight instructor realized that the airplane was not going to reach the runway, he attempted a forced landing on a small road, maneuvering the airplane to avoid buildings, trees, and power lines. Surveillance video from a nearby business showed that that airplane struck a utility pole and power lines in a parking lot about 0.6 nm from the runway threshold. The airplane caught fire upon impact with the power lines, spun counterclockwise, and fell to the ground, coming to rest upright next to the parking lot. The passenger (in the rear seat) noticed that the fuel pressure showed zero just before the airplane impacted the power lines. The fuel selector was located in the wreckage and was found fully in the OFF position. The flight instructor stated that he did not direct (or teach) the student pilot to move the fuel selector to the off position during the approach or forced landing and did not observe him doing so. The student pilot stated that he had no recollection of moving the fuel selector and that he would have taken action if he had he noticed that the fuel selector had been inadvertently moved. PERSONNEL INFORMATIONExamination of the student pilot’s logbook revealed that he had accrued 2 hours of flight time in the accident airplane before the accident flight. AIRCRAFT INFORMATIONThe accident airplane’s fuel selector valve was the original model design, which had four selectable positions in an "X" pattern. The fuel selector valve was mounted on the airplane's left sidewall near where the pilot's left leg would be positioned. The lower two detents of the "X" pattern were both OFF positions, and the forward and aft upper detents selected the right and left tanks, respectively. The valve and bezel design on the accident airplane allowed the valve to be rotated without stops or safety measures to any of the available positions, including off. The design of the fuel selector bezel and handle was subsequently modified twice by the manufacturer. The second-generation design was a three-position design with off, left, and right selections. Rotating the handle fully counterclockwise to the 9:00 position selected the “OFF” position, and rotation clockwise to the 3:00 position selected the right tank, and the intermediate 12:00 position selected the left tank. The third-generation fuel selector added a spring-loaded stop that prevented a pilot from inadvertently selecting the “OFF” position. To select that position, the pilot must simultaneously depress the spring-loaded stop and rotate the lever. Examination of the accident airplane’s logbook revealed that the fuel selector was replaced during the airplane’s last annual inspection on September 15, 2020. The entry read, “Removed and replaced fuel selector with new,” but included no reference to Service Bulletin (SB) 840A, “Fuel Selector Valve Cover Replacement,” dated November 7, 2013. The airplane manufacturer considered compliance with this SB to be mandatory because the fuel selector valve cover assembly would reduce “the possibility of pilot mismanagement of the fuel system through inadvertent selection to the OFF position, resulting in power interruption or stoppage.” The invoice for the replacement fuel selector included a certificate of conformity to confirm that the valve had the same part number (491-947) as the one in the airplane manufacturer’s illustrated parts catalog, which included a note referencing the SB. AIRPORT INFORMATIONThe accident airplane’s fuel selector valve was the original model design, which had four selectable positions in an "X" pattern. The fuel selector valve was mounted on the airplane's left sidewall near where the pilot's left leg would be positioned. The lower two detents of the "X" pattern were both OFF positions, and the forward and aft upper detents selected the right and left tanks, respectively. The valve and bezel design on the accident airplane allowed the valve to be rotated without stops or safety measures to any of the available positions, including off. The design of the fuel selector bezel and handle was subsequently modified twice by the manufacturer. The second-generation design was a three-position design with off, left, and right selections. Rotating the handle fully counterclockwise to the 9:00 position selected the “OFF” position, and rotation clockwise to the 3:00 position selected the right tank, and the intermediate 12:00 position selected the left tank. The third-generation fuel selector added a spring-loaded stop that prevented a pilot from inadvertently selecting the “OFF” position. To select that position, the pilot must simultaneously depress the spring-loaded stop and rotate the lever. Examination of the accident airplane’s logbook revealed that the fuel selector was replaced during the airplane’s last annual inspection on September 15, 2020. The entry read, “Removed and replaced fuel selector with new,” but included no reference to Service Bulletin (SB) 840A, “Fuel Selector Valve Cover Replacement,” dated November 7, 2013. The airplane manufacturer considered compliance with this SB to be mandatory because the fuel selector valve cover assembly would reduce “the possibility of pilot mismanagement of the fuel system through inadvertent selection to the OFF position, resulting in power interruption or stoppage.” The invoice for the replacement fuel selector included a certificate of conformity to confirm that the valve had the same part number (491-947) as the one in the airplane manufacturer’s illustrated parts catalog, which included a note referencing the SB. WRECKAGE AND IMPACT INFORMATIONPhotographs provided by first responders revealed that most of both wings and the fuselage were consumed by fire. The empennage remained intact, but the forward section of the horizontal stabilator and vertical stabilizer exhibited thermal discoloration. In addition, the right horizontal stabilator was bent upward about midspan. The engine remained partially attached to the firewall, and the cowling was consumed by fire. The propeller remained attached to the engine, and the spinner was crushed aft due to impact. Examination of the wreckage revealed that the engine was thermally damaged and that all accessories were destroyed. The spark plugs were removed, and the crankshaft was rotated by the propeller. Thumb compression and valve train continuity were established to all cylinders. Crankshaft and camshaft continuity was verified from the engine to the gears at the rear of the engine. No mechanical anomalies were noted with the engine powertrain that would have precluded normal operation. The upper portion of the carburetor and the throttle valve remained attached to the engine. The carburetor bowl, floats, fuel hose, and fuel inlet screen were destroyed by fire. The throttle and mixture control cables remained attached to the carburetor throttle and mixture control arms. The engine-driven fuel pump was destroyed by fire. The fuel selector handle was intact, and the fuel selector’s OFF position (as found in the wreckage) was confirmed during a field test with low-pressure air. Thermal damage to the fuel selector valve precluded movement of the selector’s control lever. ADDITIONAL INFORMATIONThe airplane manufacturer issued Service Letter No. 588 on September 3, 1971, to replace the existing fuel selector valve cover assembly with a “new and improved” cover assembly. The service letter also notified operators of an optional service kit to upgrade from the second- to third-generation design of the fuel selector valve cover and handle. Afterward, the Federal Aviation Administration (FAA) issued airworthiness directive (AD) 71-21-08 in 1971. The AD required operators of airplanes equipped with second-generation fuel selector covers and handles to comply with Service Letter 588 but did not require operators of airplanes with original fuel selector covers and handles to upgrade those covers and handles. The FAA published a notice in the Federal Register on August 20, 2013, to propose a revision of AD 71-21-08 that would include airplanes with first-generation fuel selectors. However, on July 10, 2014, the FAA issued Special Airworthiness Information Bulletin CE-14-22, Fuel Selector/Shut-Off Valve. The bulletin stated that “the fuel selector valve can be inadvertently switched off and/or may bind when switching fuel tanks and can cause a loss of power in flight” and recommended “the installation of a fuel selector valve cover designed to prevent inadvertently selecting the off position and the maintenance of fuel selector valves to prevent their binding.” According to the FAA, special airworthiness information bulletins are “information only. Recommendations aren’t mandatory.”