Federal officials questioned Federal Aviation Administration chief Michael Huerta Wednesday, wondering why so many hurdles have seemingly slowed the debut of a much-anticipated, high-tech upgrade to the country's system of managing air travel.

The undertaking, known as NextGen, promises to reduce flight delays by 35 percent, according to the FAA. While NextGen includes a bevy of projects, at its core is an effort to modernize air traffic control by transforming it from a system based on radar to one based on GPS.

That switch would allow for more direct routes, which translates into more planes in the air at any given time, fewer delays, and less fuel wasted.

Work on NextGen launched in 2003, but today, it's unclear when, exactly, that vision will be fully realized.

"While FAA has taken important steps to improve NextGen’s management... the agency has made little progress in shifting from planning to implementation and delivering benefits to airspace users," Calvin Scovel III, the Department of Transportation's inspector general, said in testimony Wednesday.

A decade ago, Congress ordered the FAA to create a plan to execute NextGen by 2025. On Wednesday, Scovel said the FAA has so far failed to meet the expectations of both Congress and aviation industry stakeholders. He cited the agency's lack of an executable plan, the many unresolved decisions about how the system will be designed, and a high turnover rate at the top of the agency as factors contributing to the project's delays.

In his testimony before the House aviation subcommittee, Scovel also noted that despite progress in some areas, NextGen "has also experienced setbacks, including cost overruns and delays on some major programs."

Indeed, several of the lawmakers said they've grown frustrated with hearing 10 years of statements from FAA officials touting the potential for NextGen.

Rep. Mark Meadows (R-N.C.) asked Huerta whether the possibility even remains for "real transformation" within the next decade. "I don't see any way we can do that at this point," he said.

Despite criticism, Huerta maintained his optimism. "I think we will be in a very different place, where we will be handling more traffic much more efficiently with a higher level of safety," he replied.

Huerta conceded that "there have been delays," but he added, "we've learned from those."

It's not the first time that NextGen has generated scrutiny. Scovel says the FAA, in a 2005 report to Congress, failed to address the cost of implementing NextGen, spell out the sequence in which it would be deployed at airports, or detail how the agency would develop the technology needed to make it a reality.

Wednesday's hearing reiterated many of the concerns include in a 2010 inspector general's report that questioned the pace of NextGen implementation and urged the FAA to establish firm requirements and reliable costs and schedules as it pursued the project.

Scovel also criticizes the agency for struggling to make the case for NextGen to the aviation industry. Getting that sector on board is crucial, since airlines will need to invest in technology in the cockpit to take advantage of the system once it debuts. But those stakeholders, Scovel notes, are skeptical and reluctant to commit money to the project, in part because previous technological upgrades FAA has pursued have been subsequently scrapped.

Scovel's reports also note that changes in key FAA leadership positions have resulted in the lack of a clear vision for NextGen. The agency has had five administrators since 2003, went all of 2012 without a confirmed administrator, and recently underwent its third reorganization in 10 years.

FAA officials also told the inspector general that the organization's "resistance to change" was also a challenge. The hiring of a new deputy administrator to oversee NextGen, however, coudl be a positive step, Scovel said.

Also causing challenges if the agency's failure to answer questions like whether air traffic control will remain a largely manual process or become more automated, or how many air traffic facilities will be needed to support the new NextGen system. Without those answers, it's difficult to move forward with NextGen.

One thing that's not contributing to challenges facing NextGen: inadequate funding. Scovel says that, historically, the FAA has had the money it needs to implement the program. However, Huerta and others warned that the House's latest appropriations plans could jeopardize the future of NextGen.