The head of the Federal Aviation Administration has not sold off his multimillion-dollar stake in the airline he led since 1999 despite a promise to do so as part of his ethics agreement, according to a Democratic senator.

In a letter to Bryan Bedford this week, Sen. Maria Cantwell said he vowed to sell all his shares in Republic Airways within 90 of his confirmation but 150 days have now passed. In Bedford's financial disclosures, he estimated that his Republic stock was worth somewhere between $6 million and $30 million.

Republic completed a merger last month with another major regional airline, Mesa Air Group. Republic's stock closed Thursday at $19.02, nearly double what it was before the deal was announced in April.

“It appears you continue to retain significant equity in this conflicting asset months past the deadline set to fully divest from Republic, which constitutes a clear violation of your ethics agreement. This is unacceptable and demands a full accounting,” Cantwell said in the letter.

Bedford declined a request for comment, and an FAA spokesperson said he plans to respond directly to Cantwell.

The agency has been in the spotlight since January, when an airliner collided with an Army helicopter over Washington, D.C., killing 67 people. The investigation has already highlighted shortcomings at the FAA, which failed to recognize an alarming number of close calls around Reagan National Airport in the years beforehand.

Then, in the spring, technical problems at the center that directs planes into New Jersey's Newark Liberty International Airport highlighted a fragile and outdated system relied on by air traffic controllers.

And in the fall, a longstanding shortage of controllers led to thousands of flight cancellations and delays during the longest government shutdown ever as more controllers missed work while going without a paycheck.

Bedford has pledged to prioritize safety and upgrade the nation’s outdated air traffic control system. Congress approved $12.5 billion for that project, and last week the FAA picked the company that will oversee the work.