More than one year ago, the Federal Aviation Administration relocated more than a dozen New York-based air traffic controllers to Philadelphia, where they continue to handle flights into and out of Newark Liberty International Airport. 

The FAA said Monday it is now asking the New Jersey air traffic controllers to stay in Philadelphia for two more years as it tries to improve staffing levels. 

Last year, a CBS News New York investigation revealed the move caused 817 flight delays at Newark within the first two weeks.   

The 14 controllers previously handled Newark air traffic from a facility on Long Island, where the FAA has struggled to train and retain staff. So far, 11 have agreed to remain in Philadelphia for another two years, the agency said. 

While FAA leaders say they are seeing improvements in the trainee pipeline, the agency is still grappling with an air traffic controller shortage. 

"It does appear they have built the staffing pipeline they had hoped to get into place by moving these controllers from Long Island to Philadelphia, but it also looks like it's taking longer than was planned," CBS News senior transportation correspondent Kris Van Cleave said. 

The initial move also drew criticism from some lawmakers and the controllers union, which did not immediately respond to CBS News New York's request for comment on Monday's development.

The FAA said Sunday it was lifting flight restrictions put in place at Newark and dozens of other major airports during the federal government shutdown.