RNAV Off The Ground Leads to ELSO at ATL and Many Advantages
Friday, June 14, 2013

Controllers at Hartsfield–Jackson Atlanta International Airport (ATL) now clear between eight and 12 more planes for departure each hour. At the nation’s busiest airport, controllers rely on Equivalent Lateral Spacing Operation (ELSO) to expedite departures.

ELSO, developed by the Mitre Corporation in 2011, added two departure routes at ATL due to an updated separation standard. The angle between departure routes decreased from 15 degrees to 10 degrees, and the time between departures was reduced from two minutes to one minute, taking advantage of Area Navigation (RNAV) technology.

RNAV technology uses predominantly satellite-based navigational aids, along with ground-based aids to more efficiently use airspace.  RNAV allows pilots to make more precise approaches and departures because they are not limited to following the path of ground-based equipment.

Originally, ATL used RNAV Off The Ground technology to assist with the many departing aircraft they handled each day.

“RNAV Off The Ground was a stepping stone to ELSO,” said Mike Ryan, NATCA Facility Representative at Atlanta TRACON (A80). “After we found out that the RNAV off the ground tracks were so precise, that allowed us to explore using less than 15 degree divergence.”

The introduction of ELSO at ATL enables simultaneous and successive diverging departure operations by creating two departure tracks for each runway end during normal runway operations.  When the weather is not conducive or the pilots are unwilling or unable to fly the RNAV routes, controllers revert back to the standard divergence.

The advantages of ELSO have somewhat of a domino effect.  Because it reduces the need for a triple departure configuration at ATL, there is a reduction in controller workload.  This also spurs fuel and time savings for departing aircraft.

“Going to a triple departure operation at [Atlanta] is not a ‘bad’ thing,” explained Dale Wright, NATCA Director of Safety and Technology.  “But it does cost the airline more in fuel due to an excessively long taxi to get from mid-field down to the south runway.  They also have to cross two runways to get there where a normal departure flow does not require they cross any runways.”

“It’s controller friendly, it's workload friendly,” stated Ryan. “The challenges are in a mixed environment.”

Aircraft must be equipped with the proper technology equipment in order to take advantage of ELSO.

“For example, the Delta DC-9’s are unable to fly the RNAV departures and as such are prohibited from participating in ELSO operations,” said Ryan. “The aircraft must be appropriately equipped to do RNAV Off The Ground and ELSO operations.”

Still, the advantages seem to outweigh the disadvantages. “I would say ELSO has delivered the biggest bang for the buck using NextGen technology,” said Ryan.

Currently, there are several airports, including Dallas Forth-Worth and Charlotte, who are using RNAV Off The Ground but ATL remains the only airport with a waiver to operate ELSO.