Tucson's Ryan Airfield faces closure of its contract air-traffic control tower in early April - unless it can make a good case to keep it open.

Ryan was on a list regulators released in late February of smaller airports that face possible tower closures because of federal sequestration cuts.

On Tuesday, the Federal Aviation Administration sent letters to operators of 189 small airports, including Ryan, saying their contractor-operated control towers face closure unless they can show that keeping them open is in the national interest.

The Tucson Airport Authority, which runs Ryan Airfield, received a letter concerning the airport west of Tucson, officials confirmed Wednesday.

The Airport Authority is preparing arguments to keep Ryan's tower open, said Danette Bewley, senior director of operations and maintenance for the Tucson Airport Authority.

Even if the control tower is closed, Ryan Airfield will remain open for flight operations, officials noted. Without a tower, pilots will have to coordinate takeoffs and landings themselves via radio and visual contact, as they do now at night when the tower isn't open.

Local aviation officials say closing Ryan's tower would jeopardize safety, noting that Ryan is a valuable reliever to Tucson International Airport and features advanced instrument-based landing technology.

In letters sent Tuesday to affected airports, the FAA 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 agency plans to finalize its decision on which towers will close on March 18. Airport officials have until next Wednesday to submit arguments for keeping their towers open.

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

The Tucson Airport Authority plans to send a letter supporting Ryan to the FAA and Arizona's congressional delegation by Monday, Bewley said.

"Our focus will be to discuss the positives of Ryan Airfield, that it is an important general-aviation and military-training airport," she said.

Besides intensive private pilot training, Ryan sometimes is used by military aircraft, Bewley noted. In all, Ryan hosted more than 122,000 "operations" - takeoffs and landings combined - last year.

The airports the FAA has targeted for contract-tower closures all have fewer than 150,000 overall operations and 10,000 commercial operations annually.

According to the most recent FAA figures, about 4,000, or roughly 3 percent, of Ryan's operations in 2011 involved military aircraft.

Industry groups such as the Airports Council International, the American Association of Airport Executives and its affiliated U.S. Contract Tower Association are lobbying hard in Washington to forestall the tower cuts, Bewley said.

The other Arizona airports on the list of possible tower closures are Glendale Municipal Airport, Phoenix Goodyear Airport and Laughlin-Bullhead International Airport.

A study released in November by the U.S. Department of Transportation's Office of Inspector General found that the average cost to operate a contract tower in fiscal 2010 was about $537,000, compared with about $2 million to operate an FAA-staffed tower.

The report said the cost difference was mainly due to smaller staffs and lower salaries at the contract towers, many of which operate mainly during the daytime.

Three contractors operate the towers in seven geographic areas, and their current contracts, which run through September 2014, are worth nearly $600 million, the report said.

The $138 million the FAA requested in fiscal 2013 to operate the contract-tower program represents just under 1 percent of the agency's total budget of about $15 billion.

Contact Assistant Business Editor David Wichner at dwichner@azstarnet.com or 573-4181.