WASHINGTON (Reuters) - The National Transportation Safety Board is conducting a new round of interviews with Boeing ( BA ) and Federal Aviation Administration personnel this week in its probe into the Jan. 5 Alaska Airlines 737 MAX 9 mid-air emergency.

NTSB Chair Jennifer Homendy said Wednesday investigators were back at the 737 plant in Renton, Washington this week for more interviews.

"We are looking at other instances where a door plug was opened and closed to make sure that those records are available," Homendy said at a U.S. Senate hearing.