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DME Math

Moderated by: rkaplan   New Topic Reply Print Author Post rkaplan Administrator Joined:  Sun Jan 22nd, 2006 Location:  Uniontown, Pennsylvania USA Posts:  387 Status:  Offline  Posted: Tue May 30th, 2006 05:13 am Quote Reply For those airplane owners installing an IFR GPS including a Garmin 430 or 530, I recommend keeping your DME if you have one in your airplane. Look at this LOC/DME 21 aproach into KPDX for example in Portland, Oregon.  The multiple stepdowns are not in the GPS approach database.  If you fly this approach without a DME, you need to do "DME Math" and calculate the distance from the FAF for each stepdown.   This approach is much easier to fly with an actual DME receiver.  For example, using the GPS approach as loaded below  I-GPO 11 is located 4nm before ROBOT and I-GPO 4 is located 2.8nm before the missed approach point; using DME the distances are exactly as charted. Jeppesen appears to be entering more stepdown waypoints over time in their database so this situation is likely to continually improve with time.    Attachment: pdxloc.jpg (Downloaded 45 times) ____________________ Richard Kaplan, CFII rkaplan@flyimc.com http://www.flyimc.com rkaplan Administrator Joined:  Sun Jan 22nd, 2006 Location:  Uniontown, Pennsylvania USA Posts:  387 Status:  Offline  Posted: Tue May 30th, 2006 05:19 am Quote Reply Another way to fly this approach on the Garmin 430 or 530 is to  use the technique described in http://flyimc.mywowbb.com/forum4/74.html and use the GPS not to formally load the approach (since the localizer is the legal navaid)  but rather to set the GPS active waypoint to IGPO and then read the GPS distance as equivalent to localizer DME.   OBS mode with the HSI set to the inbound course helps with situational awareness in this situation.  It looks like this on the GPS:   Attachment: igp.jpg (Downloaded 43 times) ____________________ Richard Kaplan, CFII rkaplan@flyimc.com http://www.flyimc.com pdxgreg Member   Joined:  Wed May 31st, 2006 Location:    Posts:  1 Status:  Offline  Posted: Wed May 31st, 2006 06:14 am Quote Reply That's odd, sometimes when you have multiple step down fixes the gps displays a fix and includes the dme distance in the name (KSPB loc/dme rwy 15 as an example). I ran the PDX loc21 and thought I was onto something as the first waypoint beyond creak ended in Q, the 17th letter of the alphabet which made some sense since the dme is 17, then the 14 dme fix ended in N. But then everything changed names and CL21 made no sense. There has to be some logic behind the gps fix names, but what is it? rkaplan Administrator Joined:  Sun Jan 22nd, 2006 Location:  Uniontown, Pennsylvania USA Posts:  387 Status:  Offline  Posted: Wed May 31st, 2006 06:31 am Quote Reply pdxgreg wrote: There has to be some logic behind the gps fix names, but what is it? You are correct regarding your understanding of DME fix terminology -- see here: http://flyimc.mywowbb.com/forum4/85.html Regarding CL21 the "C" means course fix, the "L" means Localizer approach, and the 21 means runway 21.  You can find more details starting at page 8-43 here: http://www.cheltonflightsystems.com/PDFs/50BPilotsGuide/8-Appendix-Index.pdf   ____________________ Richard Kaplan, CFII rkaplan@flyimc.com http://www.flyimc.com  Current time is 06:22 am

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