The U.S. Coast Guard is searching the waters south of Nantucket for a Canadian medical jet that disappeared early Saturday while flying from Bermuda to Boston. Six people are believed to have been aboard, the Coast Guard said. The missing aircraft, a Gulfstream G100 operated by Ontario-based Latitude Air Ambulance, lost contact with air traffic control. Nantucket Memorial Airport said the pilot declared an emergency. Flight data indicates the jet lost at least 9,000 feet in about two minutes, then flew at a steadier altitude for several minutes before vanishing. In radio communications, an air traffic controller asked the pilot, “You’re coming in blind?” A fire rescue dispatcher told emergency crews to prepare for the plane’s arrival, saying it was about 15 minutes away and experiencing electrical problems while lacking radio and radar contact, according to emergency communications audio. The Coast Guard sent two search-and-rescue planes, a helicopter and a motor lifeboat to the area. No information about the people aboard or the cause of the emergency was immediately available.