WASHINGTON, Aug 7 (Reuters) - The head of the National Transportation Safety Board said on Wednesday the Alaska Airlines Boeing 737 MAX 9 mid-air emergency was entirely avoidable because the planemaker should have addressed unauthorized production work long ago.

"This accident should have never happened. This should have been caught years before," NTSB Chair Jennifer Homendy told reporters.

"There have been numerous, numerous Boeing audits, FAA audits, compliance reviews, compliance actions plans, noting a history of an unauthorized work, unauthorized removals," Homendy said. (Reporting by David Shepardson Editing by Chris Reese)