The FAA and National Transportation Safety Board investigators are interviewing Boeing employees as they investigate the in-flight emergency that happened on an Alaska Airlines flight in January. Boeing released documents that may show instances where the door plugs were removed on a 737 Max as it was being assembled. The next step is to determine if workers documented that type of work in the past. The NTSB said Boeing still does not know the personnel who worked on the 737 involved in the incident and some investigators call that unacceptable.