Wheels started turning on a federal plan to reroute airplane traffic in the Denver metro area years ago, but after the government released more than 1,000 pages of a study on its potential effects, Centennial Airport is still urging a closer look.

“Congress has recognized that it is quite obvious that the (Federal Aviation Administration) has not sufficiently addressed, or at a minimum underestimated, the need for broad citizen participation,” said a letter from the airport's executive director, Robert Olislagers, to the FAA.

The June 5 letter came a day before the public comment period closed on the FAA's draft of an analysis of the NextGen Denver Metroplex project, which aims to optimize arrival and departure at local airports. That includes Denver International Airport, Centennial Airport and some others. The study, called a draft environmental assessment, looked at impacts the project could have on noise, air quality, wildlife, and historic and cultural resources.

The proposed change in flight paths is expected to have “no significant impacts” on those aspects of the Denver metro area, according to the study.

But Centennial Airport points to widespread backlash in other metro areas across the country where Metroplex plans have been implemented.

“Legal action was initiated against the FAA regarding (NextGen) implementations in Phoenix, Los Angeles (southern California) and Baltimore-Washington, D.C., and more communities are considering the same,” the airport wrote. Implementation “was followed by very significant increases in noise complaints in communities in northern California ... southern California (Los Angeles), Washington, D.C./Baltimore and Phoenix.”

The FAA contends that most proposed flight paths in the Denver area closely follow what are being flown today and that around Centennial Airport, the plan includes only two notable flight path changes.

It's unclear how closely other cases will mirror Denver metro's experience — the lion's share of increased air traffic over some Phoenix areas was by jets, for example, whereas larger planes have less presence at Centennial Airport.

“Centennial Airport stands with its neighboring communities, and we want the FAA to address these concerns now — not after implementation,” said Deborah Grigsby Smith, airport spokesperson.

Planes in 'volatile conditions'

Local officials across the south metro area have raised concern about the plan, but the FAA argues that one proposed route at issue, BRNKO, entails a tiny amount of traffic.

And planes today already travel the area the other proposed PINNR path would cover in the Denver area, according to the FAA. That's a proposed route that travels south, roughly above Interstate 25, starting around Greeley and turning southeast over the Denver area.

The BRNKO route — pronounced “Bronco” — would take arrivals from the northeast that currently stay east of I-25 and move them farther north, joining up with PINNR near Greeley and traveling in that same corridor as flights move south.

BRNKO only entails about six flights per day on average that would be moved from an older corridor, according to the FAA. About two daily would use a nearby route that ends up over the same south metro area. Centennial Airport sees about 1,055 daily takeoffs and landings combined.

And once BRNKO flights cross the City of Denver border into Arapahoe County, its flights would largely cover the same areas as current routes do, according to FAA maps.

But Centennial Airport argues the route will put pilots over unsafe territory: the foothills, where volatile wind conditions can be “unpredictable,” according to the letter.

“When weather or winds are not a factor, the corridor is popular with small aircraft flying in both directions, creating safety concerns as aircraft with vastly different speeds will operate in the same airspace at nearly identical altitudes,” the letter continued.

'Important environmental info missing'

The plan is expected to have “no significant impacts” on noise, air quality, wildlife, or historic and cultural resources, according to the draft of the FAA study dated April 22.

The report does note that about 100 people in rural parts of Jefferson, Adams and Elbert counties would likely experience a noise increase of 5 decibels in areas where the average noise would usually vary between 45 and 60 decibels. Conversation in restaurants generally hovers around 60 decibels, according to a Purdue University chart. Upper-70s levels are annoyingly loud to some people, the chart said.

But that's the extent of the notable noise changes, the report said — and only increases of 1.5 decibels or more in areas exposed to 65 decibels and up are considered to “exceed threshold of significance,” according to the report.

Centennial Airport’s director, however, argued that the FAA didn’t consider the impact of the part of flight that occurs below 3,000 feet above ground, and that leaves unclear how much communities could be affected. Littleton, Centennial, Cherry Hills Village, Lone Tree, Castle Rock and other nearby cities could experience notable effects, Olislagers said.

Flights “will increase over areas that have never or rarely seen overflight at lower altitudes. It is one thing when (DIA) commercial airline traffic flies over at 10,000 feet” above ground, Olislagers said. “It’s something quite different when a business jet, inbound to Centennial Airport, comes over at 2,500 feet.”

A spokesperson for the FAA did not respond with comment for this story.

In the letter, the airport also pushed for the FAA to complete more studies mandated by the FAA Reauthorization Act of 2018, a law passed by Congress, before it puts the Metroplex plan in motion.

The recent law requires the FAA to study the agency's “community involvement” practices regarding NextGen Metroplex projects; the effect of aircraft noise on communities; the relationship between noise and health impacts such as sleep disturbance and elevated blood pressure, as well as the effect on businesses located under certain flight paths; and whether 65 decibels and up remains an acceptable FAA standard for significant noise exposure, according to the airport's letter.

“Some of the results of these mandated studies could be complete around the same time that the FAA plans on implementing the Denver Metroplex,” Olislagers said. The “results of these studies could have a significant impact on the Denver Metroplex, as well as the FAA’s conclusion that there is ‘no significant impact.’”

Whether the FAA must wait until the studies are complete is unclear, Olislagers added.

“We have asked the FAA to consider waiting,” Olislagers said. “We feel strongly that postponing implementation by a few months to ensure the health and welfare of residents is far more important than the need to rush to judgement on Metroplex — especially since the FAA’s own self-imposed delays on this project clearly indicate the issue is not time critical.”