A single-engine plane has crashed into Lake Texoma in southern Oklahoma and emergency crews are searching for its pilot.Federal Aviation Administration spokesman Lynn Lunsford says the plane was conducting low passes over the lake Wednesday morning when it went down.He says the Grumman AA1 was registered out of Durant.Marshall County Undersheriff Danny Cryer says the plane crashed at least 500 yards offshore and was submerged in about 50 feet of water near the Alberta Creek Resort, southeast of Kingston.Cryer says it's believed the pilot was alone in the aircraft. It wasn't immediately known if the pilot has been found.The FAA and other agencies are investigating.The lake extends for miles along the Texas border, with the eastern portion extending northward into Oklahoma.