A Southwest plane that landed in Yuma last week due to structural problems has caused the NTSB to make new requirements for inspecting some Boeing 737 aircraft in the -300, -400 and -500 series. The 15-year-old aircraft, which had logged 39,000 pressurization cycles, a measurement of the number of takeoffs and landings, made an emergency landing after a gaping hole in the fuselage opened above the cabin of the plane approximately 18 and a half minutes after it took off from Phoenix Sky Harbor Airport. The plane was headed to Sacramento, Calif.