The Palisades Community Association asked residents to rate plane noise over their homes along the Potomac River after the Federal Aviation Administration changed flight paths at Reagan National Airport. (Ricky Carioti/The Washington Post)

The three-year battle between residents in Northwest Washington and the Federal Aviation Administration over noise from flights at Reagan National Airport is now in the hands of a federal appeals court.

The two sides presented their case to a three-judge panel of the U.S. Court of Appeals for the District of Columbia last week. A ruling, which could take several months, will be closely watched by communities across the country grappling with similar issues tied to the FAA's efforts to modernize the nation's air traffic system.

In August, a three-judge panel of the same court ruled 2-1 in favor of residents and city officials in Phoenix who argued that the agency failed to consult them when changes were made to flight paths at Sky Harbor International Airport. As part of an agreement, the FAA said it would make temporary alterations to some — but not all — flight paths.

Despite the FAA's position that the Phoenix case would not set a precedent, a ruling in favor of the D.C. residents could boost other efforts to combat airplane noise.

Oral arguments before the D.C. panel focused on two areas — whether residents met the deadline for filing their protest and whether the FAA's outreach efforts were adequate. The two sides differ on whether the changes to flight routes were fully implemented.

In court filings and his oral argument, attorney Matthew G. Adams said the FAA failed to inform — and may have even misled residents and their elected representatives — about the changes.

"This is a challenge to the FAA order that made a flight path called LAZIR the default departure route for northbound aircraft from Washington National Airport, but at the bottom, this really is a case about the FAA hiding the ball," Adams said.

Lane N. McFadden, arguing for the FAA, said the agency followed all rules for notifying the public about the coming changes. In fact, he noted, the FAA may have even gone beyond what was required by law.

But that drew skepticism from the panel of judges, who said they were puzzled that while hundreds of notices were sent to institutions, including libraries and representatives in West Virginia and Pennsylvania, none was sent to libraries or elected representatives in D.C., other than Del. Eleanor Holmes Norton (D).

"Here we have a situation where you would be in a much better position if all the agency had done was publication and some minor outreach,"Judge David S. Tatel said. "But the outreach is so distorted . . . it does leave an odd impression about what the agency was trying to do here."

McFadden said the lack of mailings in D.C. was "unfortunate" and was later found to be an "oversight" by a contractor. Even so, he said, notices were placed in newspapers, as required by law. The FAA also noted in court papers that it had informed an employee in the District's Department of Transportation.

Adams also faced scrutiny from the panel over his contention that residents had met the filing requirement. He maintained that even though the flight paths were published in 2013, they were not regularly flown until two years later, which would make the residents' 2015 filing well within the deadline.

Residents across the Washington region have complained about airport noise, but the suit was filed by those living in Northwest D.C. neighborhoods including Georgetown, Palisades and Hillandale. They say they began to notice changes in 2013, but the issue came to a head in 2015 after planes began regularly flying new routes at National. The FAA said another reason the changes were made was to reduce noise by shifting more of the flights over the Potomac River.

A recent report released by the Metropolitan Washington Airports Authority, which manages National and Dulles airports, showed that the number of complaints has not only continued to grow, but has come from a broader geographical region.

In all, airport officials logged 42,683 complaints about flights at National and Dulles in 2016, compared with just under 10,000 in 2015. The bulk of the complaints were about flights at National, and officials noted that more than half were filed by just two people.

The shift at National is part of a multibillion-dollar program, dubbed NextGen, designed to move away from the World War II-era radar system to satellite technology. FAA officials say the change will save fuel and reduce emissions because planes fly more direct routes. In Atlanta, at the nation's busiest airport, the system has helped speed up departures by 48 percent, FAA officials say.

But more direct routes also mean noise is more concentrated over certain neighborhoods.

The case is also being closely watched by residents in Maryland, where a shift in flight patterns at Baltimore-Washington International Marshall Airport has also led to a sharp rise in complaints. In October, Maryland Gov. Larry Hogan (R) directed Attorney General Brian Frosh (D) to sue the FAA.

"This isn't just ignorance of the order," Adams said. "Our elected representative inquired; there is this disparate treatment in this notice process. We are not in a situation where we're just saying we didn't happen to get your letter in time."