Critacal Dme?
 

Hi: Does any ever been flown to RJFK/KOJ (KAGOSHIMA) Japan? On their STARs, there is a small block mention about CRITICAL DME ,anyone knows what is that for? Thank s.

Critical DME has to do with your RNAV Capabilities and availability for the STAR/SID. Japan has not quite embraced pure GPS navagation so for RNAV aircraft you must also have ground based navaids for backup position recognition. So. To answer your question Lets go though the chart. Lets take the Celes Rnav Arrival to RWY 34.

In this case the box on the lower left hand corner (if using Jepps) shows the Critical DME. Let's take the Kajiki VOR for example. it has a DME Gap of 12.5 NM, so basically if the KGE VOR is inop, somewhere in this arrival there would be a 12.5nm gap in coverage of the ground based navaids to calculate DME/DME for your RNAV equipment. Obviously this is probably not a problem because most transport catagory aircraft use a FMS that has GPS/GPS or GPS/DME calculations so you're navigation performance is not degraded significantly. Most operators in Japan have a DME Gap limit for each type of aircraft flown. My aircraft for example has a max DME Gap of 14.0 nm, so if the KGE VOR (which is most restrictive) is INOP I am still ok to fly this arrival. Hope I made it clear as Mud!:cool:

Pretty much as previous post in a nut shell- ALT profile is based on the DME so its critical that you have this at all times

Thank you so much,But what is DME Gap ?:rolleyes:

From what alaskabob wrote, DME Gap is the distance where you wont have any signal coverage from the navaids the procedure is based upon.

If you have any other equipment onboard, i.e. GPS/GPS you can still fly the procedure accurate. :ok:

Things are clear now,appreciate you guys.:D:D:D

TLD is the critical DME ( station). Its about 20NM NW of Narita. So as described above, if flying an aircraft without GPS (or a NOTAM that terminal RAIM is not available during the expected time using the SID ) and the Criticial DME is NOTAMed inop then fhe RNAV 1 route ( SID or STAR ) is not available for use if the DME GAP exceeds the aircrafts limit ( Category C aircraft limit is 14NM ).

A conventional SID would need to be requested.

That's not the way I understand it. If your FMS uses GPS you can ignore the note. But, if your FMS doesn't have GPS (old RNAV airframe), and instead uses DME/DME, then the critical DME must be operative to use the STAR or SID. KSLC, for example has the same restriction. Most of the time the terminal area has sufficient DME geometry that the note isn't required for the old pre-GPS RNAV airframes.

Example at KSLC:https://cimg5.ibsrv.net/gimg/pprune....342c010608.jpg