WASHINGTON, Aug 6 (Reuters) - The National

Transportation Safety Board and Boeing ( BA ) have not been able to

determine who removed a door plug in a new 737 MAX 9 Alaska

Airlines 737 MAX 9 that suffered a mid-air emergency in

January, the board's chair said Tuesday.

NTSB Chair Jennifer Homendy told reporters Boeing ( BA ) needs to

make significant improvements to its safety practices. "The

safety culture needs a lot of work (at Boeing ( BA ))," she said. "It

is not there from the evidence itself, from what you see in the

interviews. There's not a lot of trust, there's a lot of

distrust within the workforce."