Overlay Approaches
Join Date: Aug 2013
Location: PA
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Currently that is not the case. In general i was kinda surprised upon switching from boeing to airbus how oldfashioned its avionics and especially its PFD and ND are. But that is a discussion for another thread.
Join Date: Aug 2007
Location: Egremont, MA, USA
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I'm coming late to this discussion, but let me add a couple of points.
In the US, all so-called "overlay" approaches are being discontinued. Here, an overlay is an approach that was previously labeled GPS/NDB-A, for example. When in effect, you could substitute the GPS for the NDB, even if the NDB was out of service. With the discontinuation of these approaches, the FAA has commissioned separate RNAV and, in the previous example, NDB approaches. There was an interval during which the NDB approach to my local airport was separated but the RNAV was not yet commissioned. At that point, if the NDB was OTS, one couldn't fly the approach even with GPS terminal guidance and approach wouldn't approve it. GPS is allowed to substitute for an NDB or VOR but not if it is the primary navaid for the approach.
Now, with respect to DME, GPS is allowed to substitute for DME in virtually all circumstances, at least in the US. There is a specific page in the front of the Jepps that deals with this. However, on an ILS one can only use GPS up to the FAF and must use the localizer/glideslope inside the FAF. In fact, the box will warn of this.
I think that the discussion of FMS has confused the matter, as there are multiple sensors involved. However, inasmuch as the FMS includes GPS guidance, I see no problem with using it to intercept the localizer outside the FAF on an arc with DME inop as long as the actual localizer/glideslope is tuned and used as primary guidance inside the FAF.
At least that is my understanding of the FAA's stance on the matter...I realize that individual operators have opspecs that are specific and may differ.
In the US, all so-called "overlay" approaches are being discontinued. Here, an overlay is an approach that was previously labeled GPS/NDB-A, for example. When in effect, you could substitute the GPS for the NDB, even if the NDB was out of service. With the discontinuation of these approaches, the FAA has commissioned separate RNAV and, in the previous example, NDB approaches. There was an interval during which the NDB approach to my local airport was separated but the RNAV was not yet commissioned. At that point, if the NDB was OTS, one couldn't fly the approach even with GPS terminal guidance and approach wouldn't approve it. GPS is allowed to substitute for an NDB or VOR but not if it is the primary navaid for the approach.
Now, with respect to DME, GPS is allowed to substitute for DME in virtually all circumstances, at least in the US. There is a specific page in the front of the Jepps that deals with this. However, on an ILS one can only use GPS up to the FAF and must use the localizer/glideslope inside the FAF. In fact, the box will warn of this.
I think that the discussion of FMS has confused the matter, as there are multiple sensors involved. However, inasmuch as the FMS includes GPS guidance, I see no problem with using it to intercept the localizer outside the FAF on an arc with DME inop as long as the actual localizer/glideslope is tuned and used as primary guidance inside the FAF.
At least that is my understanding of the FAA's stance on the matter...I realize that individual operators have opspecs that are specific and may differ.
Last edited by acroguy; 23rd Oct 2014 at 01:15.
Join Date: Feb 2014
Location: Spain
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But the reality is, you were in Africa, are you going to divert to the alternate just because the DME was us, knowing that probably the accuracy of you navigation capability is grater than the ground equipment ... use the airmanship ....I would landed as you, and I can understand that you were worried about the legality, as you know the real world is not perfect, so you have to balance between pros and conts
Join Date: May 2001
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Did once an LNAV/VNAV pproach on the out of service ILS in Brazzaville. Looked better than the offset VOR approach on the same rwy. As long you know what you are doing, and who is responsible..
