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It is only legal to do this if the approach is titled "VOR or GPS", you cannot fly a DME arc like this unless the approach has "GPS" in the title.
The only legal way to fly a DME arc on a VOR only approach is to put the VOR in the GPS as the 'to' waypoint. If you do this, there is no difference to the pilot when flying the approach compared to using DME. DO NOT SELECT THE 'APPROACH' in the GPS!
[/ QUOTE ] I will tone this down somewhat and say that it is ok to fly the arc in GPS mode, but not the actual approach. You should transition over to the correct navaid prior to the FAF. That is how it is often done in larger aircraft with a FMS (This is easier as larger aircraft will have DME in addition to the FMS). This is somewhat of a grey area, as to where the approach actually starts. I would argue that you must obviously be using the correct navaid prior to crossing the FAF.
From a practical standpoint, unless you have 2 GPS units, you should just fly the approach by putting the VOR in the GPS as a waypoint, as this is the way it is supposed to be flown. If you have 2 GPS units, you could fly the ARC on one unit and then have the VOR in another for correct DME during the actual approach.
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So my interest was piqued by this discussion and it caused me to reread the GPS section in the AIM and I see where it states that:
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8. Do not attempt to fly an approach unless the procedure is contained in the current, on-board navigation database and identified as "GPS" on the approach chart. The navigation database may contain information about nonoverlay approach procedures that is intended to be used to enhance position orientation, generally by providing a map, while flying these approaches using conventional NAVAIDs. This approach information should not be confused with a GPS overlay approach (see the receiver operating manual, AFM, or AFM Supplement for details on how to identify these procedures in the navigation database). Flying point to point on the approach does not assure compliance with the published approach procedure.
Then I went back and read the blurb on the GPS Approach Overlay Program:
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3. The GPS Approach Overlay Program is an authorization for pilots to use GPS avionics under IFR for flying designated nonprecision instrument approach procedures , except LOC, LDA, and simplified directional facility (SDF) procedures. These procedures are now identified by the name of the procedure and "or GPS" (e.g., VOR/DME or GPS RWY 15). Other previous types of overlays have either been converted to this format or replaced with stand-alone procedures. Only approaches contained in the current onboard navigation database are authorized. The navigation database may contain information about nonoverlay approach procedures that is intended to be used to enhance position orientation, generally by providing a map, while flying these approaches using conventional NAVAIDs. This approach information should not be confused with a GPS overlay approach (see the receiver operating manual, AFM, or AFM Supplement for details on how to identify these approaches in the navigation database).
So my first question is this: Are you able to load a precision approach from the navigation database into the GPS and fly off that?
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No, by definition a precision approach includes vertical guidance, and these cannot yet be flown with a GPS, although it is coming in the form of WAAS approaches. The GNS480 was recently granted WAAS certification, but I am not sure if any WAAS approaches have been authorized for use (a few do exist).
Unless the approach includes 'GPS' in the title, you should not fly the approach in GPS mode, you should use conventional navaids and do the approach the old fashoned way. Most overlay approaches are being replaced by GPS only approaches, and more of the overlays disappear with each revision of the approach plates.
No localizer based approaches were ever included in the overlay program and it has never been legal to shoot these using the GPS. This also applied to the LDA which is really no different than a localizer in most respects. From the wording in the AIM it sounds like it was the same for the SDF.
From a practical standpoint it was often confusing to load an approach into the GPS if you had to fly it using regular navaids anyway. The GPS will not give your distance from the navaid if you do this, and will instead count down to each waypoint on the approach. I find it is easier to just put in the navaid so I have accurate distance information displayed that agrees witht he DME distance on the approach plate. Since most of my instrument flying was done in aircraft with a RMI, I would also put in the outermarker if the ILS did not have a LOM or DME. This also works good for NDB approaches.
It is kind of funny that the FAA does not want you to use a GPS to do NDB or VOR approaches when the same agency is actually naming DME or cross bearing waypoints with 5 letter designators on all the approach plates. They are doing the same thing for the MAP on approaches where the MAP is the threshold, many are now labeled identical to a GPS approach.
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Second question: Are you able to file as an alternate an airport which only has a ILS/DME and a VOR/DME approach if you only have the GPS in your aircraft?
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No, this is covered in the AIM. If you plan on using an approach that requires an ADF, DME or any other navaid, you have to have the required avionics (and the navaid and the avionics have to be operational).
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Third Question: Why are you not legal to load a non-precision approach utilizing only the GPS if the AIM is not regulatory?
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You can load whatever you want. You just have to actually fly the approach using the required navaids.
Some will argue the AIM is not regulatory, but for all intents and purposes it is. Advisory circulars are no different. If the FAA included everything in the FARs they would be so huge that you would need a hand cart to lug them around.
The FARs contain the basic information. The AIM and the ACs actually explain what the FARs mean and give regulatory guidance. It is one thing for the FAA to allow GPS to be installed and used in aircraft. But there are TSO requirements for the design of the GPS units (TSO C-129), ACs that tell the mechanics how to install them (AC 20-138) and the AIM (1-1-20) that explains to us how we are supposed to use it.
