The air traffic controller repeated the warnings to the pilot more than a half-dozen times. Stop drifting, keep on course and a chilling, urgent plea: “Low altitude alert, climb immediately, climb the airplane.” Instead, the twin-engine plane plowed into a San Diego suburb, killing the pilot and a delivery driver on the ground and burning homes. Now, federal investigators must try to figure out what caused the crash that left a shocked and damaged neighborhood. The Cessna 340 nose-dived and clipped a UPS van in Santee after noon Monday as it was preparing to land at Montgomery-Gibbs Executive Airport in San Diego. An elderly couple suffered burns when their home went up in flames. Neighbors helped the woman out of a window. Nearly a dozen other homes in the eastern San Diego suburb were damaged. The plane was owned and piloted by Dr. Sugata Das, a cardiologist who worked in …