The Federal Aviation Administration needs another $574 million from Congress to complete phase one of a $10.6 billion air traffic control modernization plan, according to a Government Accountability Office report released Monday. Congress previously approved $9 billion for the phase, while the FAA is using $1 billion from its current-year budget. The GAO said the FAA has not fully assessed the new system’s operating costs or established a detailed schedule for completing the reforms, raising the risk of cost overruns, delays, disruptions and missed performance targets. Telecommunications upgrades have increased by $4.75 billion to $5.91 billion. FAA Administrator Bryan Bedford is scheduled to testify before Congress on Tuesday as the agency prepares to deploy software intended to help avoid flight delays. The first phase includes more than 11,000 projects, while the FAA says more than 95% of specific tasks remain largely on plan.