Tucson's Ryan Airfield faces closure of its contract air-traffic control tower in early April unless it can make a good case to regulators that keeping it open is in the national interest.

The Tucson Airport Authority has received a letter from federal regulators saying Ryan is among 189 smaller airports that face closure of their contract air-traffic control towers due to looming sequestration cuts.

The airport authority is preparing arguments to keep Ryan's tower open, under a public-comment process announced by the FAA, authority spokeswoman Katy Smith said. She stressed that no matter what happens with its tower, Ryan will continue to operate.

Ryan had appeared along with three other Arizona airports on a list released Feb. 22 of more than 200 airports that could see their contractor-operated towers closed.

In letters sent Tuesday to affected airports, the Federal Aviation Administration said it will close 173 contract towers nationwide April 7, while 16 others will close by the end of the fiscal year, Sept. 30. The agency also is considering closure of 49 FAA-staffed control towers.

The FAA plans to finalize which towers will close on March 18. Airport officials have until next Wednesday to argue for keeping their towers open.

But the FAA said it will only consider arguments that a closure would have a "negative impact on the national interest," and not concerns over local impacts.

Local aviation officials have said that closing Ryan would jeopardize safety, noting that Ryan is a valuable reliever to Tucson International Airport and features advanced landing-approach technology. Without a tower, pilots will have to coordinate takeoffs and landings themselves via radio and visual contact.

The other Arizona airports on the initial list of possible tower closures were Glendale Municipal Airport, Phoenix Goodyear Airport and Laughlin-Bullhead International Airport. It was not immediately clear whether those airports had received further notice.