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... In a report released Monday, the GAO said that 51 of the FAA's 138 ATC systems " more than a third " were unsustainable due to a lack of parts, shortfalls in funding to sustain them, or a lack of technology refresh funding to replace them. A further 54 systems were described as "potentially unsustainable" for similar reasons, with the added caveat that tech refresh funding was available to them.

"FAA has 64 ongoing investments aimed at modernizing 90 of the 105 unsustainable and potentially unsustainable systems," the GAO said in its report. "However, the agency has been slow to modernize the most critical and at-risk systems."

The report said the seemingly perilous status of 17 systems was "especially concerning" as these are deemed to have critical operational impact at the same time as being unsustainable and having extended completion dates -- the first of them won't be modernized until 2030 at the earliest. Others aren't planned to be complete until 2035, and four of the 17 "most critical and at-risk FAA ATC systems" have no modernization plans at all.
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