Quick IFR Question

[airspeedsalive]

I should know this, but I don't. We went to DFW yesterday and got the ILS to 18L - when we looked at the plates saw if the GS is out there is are 18L Y and 18L Z LOC approaches. The Z approach had lower mins, but the plates look identical. What's the difference between the two approaches? Thanks.

 

[onthebeach]

I may strike out, but I'll step up to the plate.

Pun intended.

The procedures are named "ILS or LOC Y RWY 18L" and "ILS or LOC Z RWY 18L." The "Y" and "Z" are to differentiate approaches to the same runway, using, the same navaids, but with different minima.

The confusion here is that the GS out, i.e., LOC approaches are exactly the same.

It's the full ILS that has the difference.

Note that on the ILS Y, the DH is 880 with RVR 2400 required, and there are different mins for Cat D. However, on the ILS Z, the DH is 802 with RVR 1800 required, and the mins are the same for Cat A through D.

Since a Category I ILS (which both these are) lowest vis min is RVR 2400 unless there's TD zone and RCL lighting...which this runway obviously has...I would say that the ILS Z procedure would be specified only when the weather is lower and the TD zone and RCL lighting are on.

The airport might run the ILS Y approach to 18L with sidestep to 18R when weather conditions allow, so as to devote 18L solely for takeoffs, thus expediting traffic.

That's the only explanation I can think of. Best to you.

 

[airspeedsalive]

Thanks very much - I think that seems to make sense. I've looked in the Jepps and the AIM and coundn't find any explanation anywhere.

I'm new at this jet/big-time-airport stuff and I constantly amaze myself at how little I actually know! Lots to learn.

Although I saw the Min. difference, judging by the way the approach is named I assumed the letters had something to do with the LOC approaches, and not the ILS's. I'm easily confused these days. Thanks again!

 

[VVJM265]

FYI, this is from page 5-8 of the FAA Instrument Procedure Handbook:

STRAIGHT-IN PROCEDURES
When two or more straight-in approaches with the same type of guidance exist for a runway, a letter suffix is added to the title of the approach so that it can be more easily identified. These approach charts start with the letter Z and continue in reverse alphabetical order. For example, consider the RNAV (GPS) Z RWY 10R and RNAV (GPS) Y RWY 10R approaches at San Francisco International Airport. [Figure 5-5] These two approaches to the same runway are slightly different, one includes an intermediate step-down fix and the other does not; and one allows the use of vertical navigation (VNAV) and the other does not. In order to differentiate the approaches, the FAA has labeled them Z and Y. This convention also eliminates any confusion with approach procedures labeled A and B, where only circling minimums are published. The designation of two area navigation (RNAV) procedures to the same runway can occur when it is desirable to accommodate panel mounted global positioning system (GPS) receivers and flight management systems (FMSs), both with and without VNAV. It is also important to note that only one of each type of approach for a runway, including ILS, VHF omnidirectional range (VOR), non-directional beacon (NDB), etc., can be coded into a database.

 

[FL420]

...I would say that the ILS Z procedure would be specified only when the weather is lower and the TD zone and RCL lighting are on.

Good analysis. I think you are probably right. This one had me really scratching my head.

The question is.....Why would they be turning TDZ and RCL lights on and off? Complaints from airport neighbors about the lights? Not unheard of. Expense of having the lights on? Again, not unheard of. IIRC, from a year and a half ago, didn't they have some construction going on at 18L or 18R?

The airport might run the ILS Y approach to 18L with sidestep to 18R when weather conditions allow, so as to devote 18L solely for takeoffs, thus expediting traffic.

Another good point but IIRC, they usually do use 18L for takeoffs and 18R for landings anyway. Rwy 18L only has a MALSR(Cat 1 only) while 18R has an ALSF-2 with red side row bar lights(Cat I, II and III.)

Maybe ATC must turn off the TDZ and RCL lights on 18L and can only approve the ILS or LOC Y RWY 18L approach when conducting simultaneous parallel dependent ILS approaches to 18R so pilots shooting an approach to one runway don't confuse the other one when breaking out near minimums. More likely, TDZ lights are awfully bright and can be distracting when you are trying to takeoff so it would make sense to have them off on 18L when using it for takeoffs and using 18R for landings.

Just brainstorming here but am guessing it has something to do with the close proximity of Rwy 18R to 18L.

 

[airspeedsalive]

Thanks for the input guys - maybe it wasn't a stupid question after all!