May 31, 2017
Citing its concern for altitude deviations and the resulting unforeseen workload increase, NavCanada on May 19 temporarily suspended implementation of new International Civil Aviation Organization (ICAO) “climb via SID” and “descend via STAR” phraseology it had adopted on April 27. The agency has reverted to the phraseology rules that were in place prior to this changeover, and these rules are expected to remain in place until Oct. 12.
NavCanada had instituted its new phraseology to be consistent with ICAO changes for standard instrument departure (SID) and standard terminal arrival (STAR) phraseology. Previously, the clearance phraseology included both lateral path as well as vertical constraints.
ICAO adoption of the new phraseology signaled international acceptance of “climb via” clearances that the FAA implemented in 2014, but the effort to harmonize ATC phraseology did not change some key differences in the ICAO-member specific procedures that implement “climb via” and “descend via” clearances. These differences likely contributed to the resulting altitude deviations and increased workload experienced by NavCanada upon adoption of the phraseology.
When an FAA controller issues a “descend via” clearance, it tacitly cancels any ATC-assigned speed restrictions, said Rich Boll, chairman of the NBAA Access Committee’s ATC, Airspace, and Flight Technologies Working Group. When NavCanada issues a “descend via” clearance, the controller expects pilots to comply with any ATC-assigned speed in lieu of the speed(s) published on the chart.
ICAO also allows controllers to issue unrestricted “climb” and “descend” clearances that cancel both speed and altitude limits published on the SID and STAR charts. The United States does not have a clearance like it, said Boll. When a U.S. controller issues a “maintain climb/descent clearance, the published restrictions apply unless the controller specifically cancels them,” he said.
A number of ICAO member states have implemented its “climb via” and “descend via” procedures, including Brazil, which adopted the terminology following an NBAA presentation on the subject, said Boll. Ultimately, when flying internationally, U.S.-based pilots must always remember that harmonized ATC phraseology does not always equal harmonized clearance parameters.