LOC Z vs. LOC Y

[Hayden Young]

I was shooting the ILS to runway 6 at KSBD today when I noticed that SDB has 2 localiser approaches. The only differences are a steeper approach angle and a different MAP on the LOC Y, and lower minimums on the LOC Z. If both of these approaches have the same profile, why are the S-LOC minims lower on the LOC Z? I have posted links to the charts below.

http://skyvector.com/files/tpp/1310/pdf/00547ILZ6.PDF
http://skyvector.com/files/tpp/1310/pdf/00547LY6.PDF

[Pieces]

Possibly to allow a lower climb gradient on the missed? If you can't maintain a standard climb, use LOC Y. I don't know if that is the actual answer, but that'd be my guess.

[Brian Z]

I hope I can help out with the discussion, but I still have to figure one thing out. The difference in the descent angle has to do with the altitude at the FAF. Both localizer approaches have an altitude of 3300 at the FAF, but the ILS is 182 lower at 3118. I think the difference in MDA has to do with the MAP and the obstacle just south of the field since the circling minimums are the same respective to both approaches. I am still trying to figure out why the 800 foot difference in MDA between the Y and Z. The only thing I can think of is it has to do with the mile difference in the MAP.

If you break down the numbers the missed approach profile sort of make sense. I am guessing the profile has to do with the two towers SE of the field over 1400 MSL. Let's look at LOC Y. The altitude at the MAP is 2480 and we need to climb to 3100 before making a turn. The standard climb gradient will take 3.1 NM before the turn. The profile in the Z has the altitude of 1640 at the MAP and a climb to 2700 before the turn. That is 5.3 NM before the turn or 1.2 NM past the turn for the LOC Y approach. By the time the turn is made and tracking inbound to the PDZ VOR the would be roughly the same in the same general area between the two missed profiles.

One point to consider is, other than timing, how are both MAPs identified?

Brian

[jtek]

Possibly to allow a lower climb gradient on the missed? If you can't maintain a standard climb, use LOC Y. I don't know if that is the actual answer, but that'd be my guess.

Bingo. This is the answer. It says so right on the chart, in the top-right of the plan view: "Missed Approach obstructions require a minimum climb of 280 feet per NM to 4300. If unable to meet rate of climb, see LOC Y Rwy 6."

[Hayden Young]

Shortly after making this post I noticed that note. Thanks for the help guys!