The U.S. Coast Guard spent hours Thursday searching waters off Louisiana for four people who were on board a helicopter that crashed into the Gulf of Mexico. The helicopter crashed as it was departing an oil platform about 8:40 a.m. CST, said Petty Officer Jose Hernandez, a spokesman for the Coast Guard’s 8th District headquartered in New Orleans. Crews searching by boat and helicopter had found no sign of them by the middle of the afternoon.