Todd Inman said he received notice on Friday from the White House personnel office that his position on the board was "terminated effective immediately" but hadn't been given a reason.
He was investigating the January 2025 midair collision between the passenger jet and Army helicopter that killed 67 people, leaving debris strewn in Washington's Potomac River.
The White House had no immediate response to a message left by The Associated Press seeking comment.
The NTSB has a five-person board but its website on Sunday showed just three members. The board's vice chair, Alvin Brown, was abruptly removed last year.
Brown and Robert Primus, who served on the US Surface Transportation Board, were the only Black board members overseeing their respective independent agencies when they were fired last year.
Both have challenged their firings in court, and the group Democracy Forward has filed discrimination claims on behalf of the men.
The NTSB is tasked by Congress with investigating aviation accidents and significant rail, highway, pipeline and other disasters to determine their probable causes and make recommendations aimed at avoiding similar incidents.
Inman also was the lead board member of the investigation into last year's crash of a UPS cargo plane in Kentucky that killed 15 people. After major incidents, the board sends a member to the crash site for initial briefings and to oversee the initial investigation.
In a statement, Inman said having been the board member on scene "for two of the largest aviation incidents in the past two decades, working with all of the impacted families and first responders has made me appreciate how the original mission of the NTSB is more crucial now than ever before".
Inman praised the NTSB staff and investigators as "world class".
"My only hope is that the NTSB leadership and those who control it stay true to its roots and culture as the pre-eminent safety organisation unimpeded by political or personal agendas," he wrote.
