Climb/Descend Via

fms

I was recently in Arizona for a 135.293 oral exam with the FAA and learned that the local FSDO has been seeing quite a few pilot deviations due to misunderstandings about the appropriate altitudes to fly when given a “climb/descend via” departure/arrival procedure.

To be honest, until I started flying internationally, it was somewhat rare to encounter a “descend via” instruction. It seems more common in Europe, probably because many domestic STARs contain “expect” altitude restrictions, and ATC is specifically prohibited from giving descend-via instructions on those procedures. (It’s also worth noting that pilots are not expected to comply with published “expect” restrictions in the event of lost communications, unless ATC has specifically advised the pilot to expect these restrictions as part of a further clearance.)

As far as “climb via” is concerned, it’s even rarer because thus far it has not been used in the United States. That’s going to change next month, however. NBAA recently published a short primer about it:

The new “climb via” instruction for standard instrument departures (SIDs) mirrors the similar “descend via” instruction already being issued for standard terminal arrival route (STAR) procedures. Under the new clearances, pilots need to pay close attention to intermediate-altitude and speed restrictions, notes NBAA Access Committee member Rich Boll.

“Many SID procedures also have published, intermediate-altitude restrictions, including ‘at,’ ‘at or below’ or ‘at or above’ restrictions, which must be followed for ATC separation purposes,” he said. “When issued a ‘climb via’ clearance, pilots will be expected to abide by all restrictions listed on the procedure when vertically navigating the SID and climbing to the initial ‘maintain altitude’ published on the SID.” Failure to comply with the charted SID procedure could result in a pilot deviation.

Along with charted altitude restrictions, pilots will also be required to comply with published speed restrictions on instrument flight procedures, though controllers can still issue speed adjustments. But once the adjustment is no longer required, ATC may advise aircraft to “resume published speed,” with no additional guidance provided.

In theory, the “climb/descend via” instruction will increase efficiency by eliminating some of the radio communication that takes place as controllers verbally provide each altitude change to the flight crew during an a SID or STAR. I say “in theory” because I have a feeling the read backs are going to cause some frequency congestion of their own until pilots get the phraseology straight. If in doubt about what a clearance means, pilots should ask for clarification, and that will eat up some bandwidth, too.

NBAA has a comprehensive tutorial available online. It’s free even if you’re not an NBAA member, so if you fly IFR, I highly recommend reading through it. The “climb/descend via” instruction is one case where pilot read back phraseology is critical. I imagine it’s going to be much like runway “hold short” instructions — if you don’t read back the instruction properly, ATC will keep bugging you until they hear the words they need to have on tape. On the plus side, if your aircraft is equipped with VNAV capability and autothrottles, these clearances should simplify SIDs and STARs because the altitude and speed profiles are part of the FMS database.

The FAA has published Notice 7110.584, which goes into effect August 15th and officially explains the phraseology and meaning. If you’re the type that prefers to watch rather than read, they also put out a 15 minute video, however the sheer physical size of the co-pilot was distracting enough that I went back to the PDF file. I’m not kidding.

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