Hello All, Dont know if this has been mentioned before. While flying the 737NGX from KJFK-KDTW I noticed in the FMC KDTW arrivals that there are two 04L runways each with a different radio ILS signal. I selected ILSY 04L and on arrival and in the approach course038 the aircraft was flying straight but about 5 degrees off to the right. I made enquiries about this and it seem that ILSZ 04L should be used instead. Both these runways are listed in the Navigraph Ndac. Anyone else found this occurrence before. Richard Welsh.

Here is your answer!

 

http://forum.avsim.net/topic/343475-ils-y-and-ils-z/

 

Best regards

Vegard Mardahl

Hello Vegard, Thanks for your reply. I dont know how you managed to find that Forum link. Richard Welsh.

For what it's worth, have a look at AirNav next time. The approaches are listed in the order of most frequent use.

http://www.airnav.com/airport/KDTW

 

I'm not as familiar with the DTW stuff as I would be with Potomac or NorCal/SoCal approaches, but the standalone ILS Y 4L seems to be just a backup to the Z. Its primary purpose is below those approaches (on AirNav). If you scroll further down the page, you'll see ILS PRM RWY 04R (SIM CLOSE PAR), and ILS Y PRM RWY 04L (SIM CLOSE PAR). Basically, the two runways are too close together to run ILS to both with the proper separation, so in order to keep more separation for a longer period of time, the localizer for 4L is pushed away from 4R by two degrees. When the plane descends into visual conditions, it will call the plane on 4R in sight and proceed visually. Once the plane has visual, radar separation rules no longer apply.

 

For more, research SOIA.