On August 20, 2000, at 1330 central daylight time, a Piper PA-28-140 airplane, N41375, was substantially damaged when it impacted terrain during a forced landing following a loss of engine power near Ennis, Texas. The flight instructor and one passenger received minor injuries and the two other passengers were not injured. The aircraft was registered to a private individual and operated by Aviation Training Center of Lancaster, Texas. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 instructional flight. The local flight departed the Lancaster Airport at 1300. According to the FAA inspector, who responded to the accident site, the flight instructor reported that while maneuvering, the engine cowling blew open. She added that she then heard a "loud bang and the engine quit." Examination of the airplane by the FAA inspector revealed that during the forced landing, the nose landing gear collapsed, structurally damaging the firewall. The FAA inspector found that the fuel valve selector was positioned to the left fuel tank. Upon recovery of the aircraft, salvage personnel affirmed that the left fuel tank was empty, while the right fuel tank contained approximately 15 gallons of fuel. On October 10, 2000, examination of the wreckage by the NTSB Investigator-in-charge (IIC) revealed that the electric fuel pump was dry and the filter was clean. No fuel was found in the lines between the electric pump and the sump. In addition, there was no evidence of fuel in either the bowl of the carburetor or the carburetor accelerator pump. The carburetor fuel filter was clean and the float operated freely without binding. The NTSB IIC was able to attain thumb compression with indication of valve movement on all cylinders by manually rotating the propeller. Magneto timing was found to be within operating limits and sparks were produced at the bottom four spark plugs when the starter was engaged. The fasteners for the right side cowling were found missing. According to the pilot, following the accident, upon request of the local authorities, she unsuccessfully attempted to reposition the fuel selector valve from the right fuel tank position to the off position in order to prevent fire hazards. The pilot stated that she was only able to move the fuel selector valve from the right fuel tank to the left fuel tank position. The NTSB IIC examined the fuel selector and discovered a fuel selector valve safety tab that prevents inadvertent fuel shutoff. The safety tab must be depressed in order to relocate the selector valve to the off position. At the time of the accident, the flight instructor had accumulated 536 total flight hours, of which 23 flight hours were accrued in the PA-28-140.