DALLAS (AP) — All six people aboard a small plane were killed Monday when the aircraft crashed into the rocky hills of a central Texas ranch while preparing to land, authorities said.The twin-engine aircraft went down just before 9 a.m. as it was approaching an airport in Kerrville, a city about 70 miles (110 kilometers) northwest of San Antonio, according to Federal Aviation Administration spokesman Lynn Lunsford.The pilot and the five other people aboard the plane were all killed, said Sgt. Orlando Moreno, a spokesman for the Texas Department of Public Safety. The names of the individuals haven't been released. State law enforcement officials secured the crash site ahead of FAA and National Transportation Safety Board investigators' arrival Monday.The Beechcraft BE58 took off from an airport outside Houston earlier Monday and crashed about 6 miles (10 kilometers) northwest of Kerrville Municipal Airport, Lunsford said. The flight was not a scheduled commercial route, he said.The downed plane was a manufactured by Raytheon Aircraft in 1999 and was co-owned by two people, according to FAA records.The cause of the crash hasn't been determined. There was a low layer of broken clouds but no rain in the area around the airport at the time of the crash, according to National Weather Service meteorologist Cory Van Pelt.