U.S. National Transportation Safety Board vice chairman Bella Dinh-Zarr has stepped in as acting chairman, as Christopher Hart’s term in that role has ended. Hart, who remains on the Board, was appointed to a two-year term as NTSB chairman on March 15, 2015.

Hart has served on the Board for nearly a dozen years, first from 1990 to 1993 and then returning in 2009. His current term as a Board member continues through the end of this year.

Dinh-Zarr joined the board in March 2015 and was immediately appointed vice chairman. She brought a background in highway safety to the NTSB, having previously served at the National Highway Traffic Safety Administration, AAA and other highway safety organizations. By statute, the vice chairman becomes the acting chair until a permanent chairman is appointed.

A permanent successor is one of several openings on the Board. The safety body is set up to have five members, but has been down one member since 2014. Additionally, the terms of Earl Weener and Robert Sumwalt have expired, but both members continue to serve on the Board.

Board members are nominated by the President and confirmed by the Senate. The President also designates the chairman.