The National Transportation Safety Board's preliminary report into the fatal collision between an Army Black Hawk helicopter and an American Airlines regional jet in January contained the recommendation that the Federal Aviation Administration permanently restrict helicopter flights around Ronald Reagan Washington National Airport.  

The FAA agreed to implement the NTSB's recommendation. Still, some travelers were left wondering about other parts of the national airspace where commercial flights and other kinds of aircraft, including helicopters and general aviation planes like small Cessnas, can be in close proximity.

Experts say this so-called mixed-use airspace is common throughout the country and is generally safe. However, almost everyone agrees that a closer examination is needed after the disaster at DCA. 

Here's where things stand and what stakeholders hope the next steps will be for regulators. 

The NTSB's recommendations 

The NTSB is still investigating the crash at DCA, but its preliminary report showed that the helicopter appeared to be out of its designated flight path. As a result, the agency recommended that the FAA permanently restrict helicopter flights around DCA. The FAA, which the Department of Transportation oversees, agreed to implement that recommendation. 

"The FAA is taking a series of steps to improve safety around Ronald Reagan Washington National Airport (DCA) that follows with the NTSB's recommendations," the agency said in a statement. "The FAA will continue to closely support the NTSB-led investigation and take action as necessary to ensure public safety." 

What is mixed-use airspace? 

Mixed-use airspace is exactly what it sounds like: parts of the sky that multiple kinds of aircraft can use simultaneously. 

In general, airspace is mixed-use by default. Certain restrictions apply to military corridors and takeoff and landing paths around major airports, but broadly, the skies above the U.S. are open. But it's not a free-for-all, either.