Y or Z?

A CJ2 flight into Jackson Hole, WY brought up an issue that confuses many instrument pilots- what does an X, Y or Z in the approach title signify?  Examples are the KJAC ILS or LOC Z Rwy 19, or the KSFO RNAV (GPS) Y Rwy 19L.

The answer is fairly simple, but like many answers, it only begs further questions be asked.  When there exists more than one approach of a given type to a specific runway, the approaches will be titled uniquely by including Z, Y, X, etc… in the title.  Thus the presence of an RNAV X Rwy 9 approach at an airport implies there are at least three RNAV approaches to runway 9.  If only two exist, they will be Z and Y; the convention starts at Z and works backwards into the alphabet.  Letters at the end of the alphabet are used so there is no confusion with the labeling for circling-only approaches, which are named with letters starting with A, moving into the alphabet  (The first circling-only VOR approach at an airport is titled VOR-A, the next is VOR-B, etc…).

So why would there be more than one approach of a given type to the same runway? Wouldn’t the FAA just make one approach as “good” as possible?  I’ve identified three broad reasons this isn’t always a viable option- for this post we’ll look at the reason Jackson has two ILSs.

Here, the difference between the Y and Z can be subtle to spot.  Looking at the profile and plan view of the charts, the Y and Z ILS seem to be identical procedures.  A careful look shows the ILS minimums are different, though. The Z approach brings a plane down to 200’ above TDZE, and requires ¾ mile visibility, while the Y only goes down to 612’ above TDZE, and needs 2 miles visibility.

So why would anyone shoot the Y? The answer lies in the notes.  On the Z approach is stated “Missed approach obstructions require a minimum climb gradient of 245 feet per NM to 11200; if unable to meet rate of climb, see ILS or LOC Y RWY 19.”

The standard gradient for a climb that is part of an IFR procedure is 200’ per NM.  If this gradient will not ensure adequate separation from terrain, a higher gradient may be required.  This is commonly seen on departure procedures, but as an aircraft starts a missed approach from a few hundred feet up, and from a point often before the runway starts, it’s uncommon to see a missed approach that requires a non-standard gradient.

 

By starting the missed approach 412’ higher, and almost 1.5 miles further from the runway, an aircraft conducting the Y approach will maintain adequate separation even if only climbing 200’/ NM.

Don't B too Fast

At first, I was surprised reading a recently published article which stated that exceeding the "200 KIAS Under Class B" limit is the most common violation for turbine pilots.  But really I shouldn't have been, as the rule has two great ingredients to bake up a violation:

1. It's easy for ATC to know you've violated it, and

2. It's easy to violate.

Both departures and arrivals can create great chances for this particular bust.  Taking off from BED, Mass, for example, aircraft are invariable cleared to a 2,000' initial altitude.  Depending on the direction of take off, the floor of the BOS Class B lies at either 3,000' or 4,000', so an aircraft leveling at 2,000' must remain at or below 200 KIAS even when out of the Class D speed restriction area (4 NM).  This can be especially difficult for a lightly loaded and/or very high performing airplane.  The pilot must contend with not only a quick level off shortly after gear and flap retraction, but must simultaneously keep airspeed down.

One technique than can help in this situation is use a thrust commanded climb once cleaned up.  Set the FD/ AP to an indicated airspeed mode slightly below 200 KIAS, and reaching 1,000' before the level-off reduce thrust as necessary to maintain an approximate 1000 FPM climb rate.  As the aircraft levels off it will be significantly easier to keep speed in check than had the climb been at full power.

Arrivals can create a more vexing situation where simply knowing when the aircraft is under Class B airspace can be difficult.  This is especially true in aircraft with legacy avionics lacking a moving map or with a basic map lacking Class B boundaries.  But even new aircraft with a G1000 based system display only the lateral limits of Bravo airspace on the MFD; determining where the floor is requires active button pushing and knob turning.

As individual sectors can be mere miles across, a pilot can be faced with determining the floor of several sections in quick succession, while simultaneously configuring the plane for landing, receiving rapid heading and altitude changes, and monitoring ATC in what's obviously a busy environment (or it wouldn't be Bravo to begin with).

To add to the fun, ATC can't authorize a speed over 200 KIAS below the Bravo- if assigned 230 KIAS, for example, it's incumbent upon the pilot to slow to 200 if altitude clearances will take the aircraft out of the Bravo.  FAR 91.117(c), which spells out the Bravo speed restriction, doesn’t contain the verbiage “…unless otherwise authorized or required by ATC…”, which is included in the restriction on Class C and D airspeed.

Heads up out there!