Numerous” close calls at airports with certain layouts and independent takeoff and landing operations have prompted the NTSB to ask the FAA for changes to certain air traffic control procedures.

In a recommendation letter published July 1, the NTSB asks for new separation standards to set the procedures controllers use in situations in which an aircraft departs one runway and another aircraft is performing a go-around on a different, non-intersecting runway.

The NTSB says standards exist for controllers to provide separation between two aircraft that are departing from runways “that do not physically touch but have intersecting flight paths,” but there is no requirement for controllers to provide the same protections “for the potential go-around flight path of a landing aircraft even though, in the event of a go-around, the arriving aircraft effectively becomes a departure.”

In the letter, the NTSB cites five cases of “hazardous proximity” that occurred when one aircraft was performing a go-around under the watch of one controller, and another aircraft was departing a non-intersecting runway controlled by a different tower controller using a different radio frequency.

Of the four such incidents that took place in 2012, two occurred at Las Vegas McCarran International Airport, one at Charlotte Douglas International Airport and one at the John F. Kennedy International Airport in New York. A fifth incident occurred in 2006, also at McCarran.

Common themes in the incidents include an unplanned go-around taking place simultaneously with the takeoff of another aircraft on a different runway, air traffic control procedures that allow independent takeoff and landing operations (separate tower controllers directing the operations on the two runways using separate frequencies) and non-intersecting runways with intersecting arrival or departure paths.

In a July 30, 2012, incident at McCarran, a Spirit Airlines Airbus A319 executing a go-around came within 1,300 ft. laterally and 100 ft. vertically from a departing Cessna Citation 510 business jet. At Charlotte on July 14, 2012, an Air Wisconsin Bombardier regional jet taking off came within 1,800 ft. laterally and 100 ft. vertically of a departing JetBlue A320.

At McCarran on April 26, 2012, a departing Learjet 60 pilot at one point climbed at 6,000 ft./min—setting off the aircraft’s stick shaker stall warning system—in order to avoid a JetBlue A320 performing a go-around.

In these incidents, the NTSB says separation was established “by resorting to impromptu evasive maneuvers by pilots during critical phases” of flight.

“Conflicts such as those described in this letter would have been clear violations of FAA safety and separation standards had the scenarios involved two aircraft departing the airport rather than one arrival and one departure,” the NTSB says. “There appears to be no safety justification for treating the situations differently.”

The NTSB is asking the FAA to create separation standards between an arriving aircraft performing a go-around, and “any combination of arriving or departing aircraft operating on runways where flight paths may intersect.”