So the LOC/DME-E approach to KASE lists for the missed approach course to use the I-PKN localizer, but then there's a note 'course outbound is normal sensing'. Does that mean that in effect, this particular LOC is installed 'backwards' so when flying away from it you get normal indications? How common is this? Only for LOC-defined missed approaches?
Notice that in the plan view, the shading of the localizers are on the opposite sides. If you are flying south-west, the actual localizer used for the approach has the shading on the right, while the one used for the missed approach has the shading on the left. This can also be used to tell you what sensing to expect. The note is also there to make it more obvious that the sensing will be backwards from what you might expect when flying outbound on a "normal" localizer.
So yes, this particular localizer is designed to transmit backwards and you will get indications that would be normal while flying inbound when flying outbound on the missed.
I'm guessing that because of the high terrain/mountains in the area that they wanted to make it as easy as possible to fly without getting confused as to which way you are supposed to turn. Combined with the fact that it is never used in a situation where you would be flying inbound makes it a perfect candidate to reverse the sensing. Unfortunately, in my mind it actually makes it harder to understand. We are taught from the beginning of our instrument training how to handle flying a localizer outbound, and now we have to do it the opposite way. Rather confusing if you ask me, but you get used to it.
As far as "how common is it", this is the only one that I've seen (but I'm guessing that there are others)....
This procedure is unusual mainly because it uses a remotely installed localizer for a missed procedure. A backcourse used in a localizer approach is not unusual, the uniqueness here is that that the localizer back course being used is not the one which was used to approach the runway. This procedure calls for flight away from the localizer transmitter during the missed approach, just as many other missed approaches would do. Contrast this with a typical final approach segment of a conventional localizer approach in which the aircraft on approach flies toward the transmitter.
I would not say that this localizer is designed to transmit backward any more than any other localizer with a back course is designed to transmit backwards. It is simply a matter that it is the back of I-PKN that is in use for the procedure. Since the course is outbound from the transmitter on the back course, sensing is not reversed, and the chart has been designed with a note to remind the pilot of that fact.
To further convince ourselves that this localizer is a run-of-the-mill navaid, picture an airplane on the missed approach procedure, outbound on a course of 303°. Now slew that aircraft backward to a point Southeast of the transmitter, still on a heading of 303°. It is now inbound toward the transmitter and sensing is in the same direction, not reversed. There is simply not a runway to be found directly prior to the transmitter. Passing over the transmitter, course does not change and sensing does not change.
The key issue here seems to me how to set up the instruments and what the indications will be. For an HSI you set the CDI to the front course, i.e. in this case to 303 and you will get correct sensing. For the old CDI/OBS because you are going “backwards” on a backcourse, you will get correct sensing (as the chart states). The reason they appear to have used the otherwise odd idea of flying outbound on a backcourse is so you do get correct sensing (and because there is not a mountain high enough and far enough away to use a localizer front course!).
I-PKN localizer is not designed to "transmit backwards." In my opinion, it's actually the normal backcourse of the I-PKN localizer antenna that sits on a 11000 ft mountain. Its only purpose is to serve as part of the missed approach procedure at KASE (and a departure procedure from KASE) . The front-course is not used because there is no airport, runway etc. associated with this localizer antenna's front-course. (It is essentially just a navaid sitting on a mountain)
When you fly a localizer backcourse signal in the opposite direction (like some missed approach procedures require after flying the front-course and then executing a missed approach) you are getting normal sensing.
The reason why the note on the plate states that I-PKN is "normal sensing" when flying its backcourse is to reinforce the fact that it is "normal sensing" and eliminate any confusion (which apparently is not always the case). Having a separate localizer antenna installed by itself away from an airport and serving solely as a missed approach navaid is unusual.