President Donald Trump’s own policies have prompted departures of key staff and hurt morale at the aviation agency, complicating multi-billion dollar modernization plans.

The Trump administration has announced a plan to replace the country’s aging air traffic control system with an all-new technology—but needs Congress to allot tens of billions of dollars.

U.S. Transportation Secretary Sean Duffy on Thursday will call for tens of billions of dollars to overhaul America’s strained air traffic control system to address crumbling infrastructure, dramatic staffing shortfalls and failing technology.