IFR Fix: The Z-Y-X of IAPs

September 28, 2012

What’s the difference between GPS and (GPS) in an instrument approach’s name?

If straight-in instrument approach procedures (IAPs) have a runway number in their title, and circling approaches get letters, why do some IAPs have both?

It all flows from the FAA’s IAP naming convention, which sounds like a conference held on the deck of an aircraft carrier, but actually is a nuanced system for naming IAPs as descriptively as possible.

IFR charts arrive on a 56-day cycle. Before downloadable procedures, it was irksome to keep volumes current and track changes between expirations.

If you weren’t going to be flying soon, it was informative to flip through a region’s approach volume to see what IAPs people fly at other airports. (Check out the challenging six-step missed approach on an ILS approach at Rutland-Southern Vermont Regional Airport. That ILS is a brand-new IAP released Sept. 21, available in two flavors designated Z and Y, and improving on two localizer-only approaches.)

Most IFR pilots can explain that IAPs not considered straight-in (for several possible reasons) get a letter in their titles, such as the VOR or GPS-B approach to California’s Palm Springs International Airport. But there’s more to the FAA’s naming convention than that, as discussed in Chapter 5 of the Instrument Procedures Handbook.

For example, GPS appears in many approach titles, but they’re not created equal. A GPS approach overlaid on another nonprecision IAP has GPS added to the title as shown for Palm Springs. A stand-alone GPS approach title might be GPS RWY 8.

Another type is this RNAV (GPS) RWY 5 approach. Under the naming convention, “RNAV (GPS) IAPs are authorized as stand-alone approaches for aircraft equipped with RNAV systems that contain an airborne navigation database and are certified for instrument approaches.”

Yes, there are approach titles containing both a runway number and a letter: The two ILS approaches to Rutland’s Runway 19 are ILS or LOC/DME Z RWY 19, and ILS or LOC/DME Y RWY 19.

There can be numerous differences between a Z and a Y procedure, but the Z approach will have lower minimums. Another rationale for reverse-alphabetically naming straight-in IAPs is to eliminate “confusion with approach procedures labeled A and B, where only circling minimums are published,” under the naming convention.

A caution: Don’t get so wrapped up in names that you select the RNAV (GPS)-B to 52B (Greenville, Maine, seaplane base) when you need an approach to nearby 3B1 (Greenville Municipal Airport), unless you are on floats.