National Transportation Safety Board spokesman Keith Holloway said investigators were interviewing the pilot and co-pilot in person in Minneapolis. He would not provide additional details, but did say the NTSB would not comment on the substance of the discussions until Monday at the earliest.
Northwest Airlines is cooperating and doing its own internal investigation, said Chris Kelly, a spokesman for Northwest Airlines' parent company, Delta Air Lines Inc.
Air traffic controllers tried for more than an hour Wednesday night to contact the Minneapolis-bound flight, which later turned around and landed safely. First officer Richard Cole has said he and the captain were not sleeping or arguing in the cockpit, but hasn't explained their lapse in response and the detour. The Wall Street Journal reported on its Web site Sunday that the pilots planned to repeat their story to safety investigators during Sunday's interview.
