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The AIM 1-1-17 2 (a) states:

Aircraft using un-augmented GPS (TSO-C129() or TSO-C196()) for navigation under IFR must be equipped with an alternate approved and operational means of navigation suitable for navigating the proposed route of flight. (Examples of alternate navigation equipment include VOR or DME/DME/IRU capability). Active monitoring of alternative navigation equipment is not required when RAIM is available for integrity monitoring. Active monitoring of an alternate means of navigation is required when the GPS RAIM capability is lost.

Does this mean that if I have a non-WAAS GPS unit then I have to file only along Victor airways or between VORs? Or can I file DIRECT?

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    $\begingroup$ Giving up a little on my age here. A long time ago, I was on a return flight home at FL250 in a Seneca II. On an IFR flight plan using VORs. ATC asked me if my LORAN was working. My reply was yes, but not certified for IFR. ATC then asked if I could tell him what my initial heading would be for my destination, I replied with the information. ATC then cleared me direct to home. $\endgroup$
    – Mike Brass
    Nov 30 '19 at 6:42
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This question was answered here on this Website. Read the second answer.

Yes you can file direct even without a GPS. However it would be advisable to perform a RAIM check during your pre-flight along your intended route and determine that you would be in RAIM during the route. If for some reason your GPS loses RAIM capability then you should proceed using VOR/DME/ADF. You can still fly direct with using only VORs although that will be more difficult.

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In my opinion, navigating an IFR flight plan is more than just the ability to get from one airport to the other. I am also concerned about communication radio failure. If you follow the advice listed in the AskACFI website, you will not have many options if your communication radio fails

It is this reason, why service volumes (see AIM 1-1-8) for VOR and NDBs are published. Assuming there are no restrictions listed in the chart supplements booklet, you can fly from VOR/NDB to VOR/NDB as long as you stay within the service volume. If you lose communication radios, at the very least you will be able to revert to the requirements listed in FAR §91.185.

I once filed TUS to IWA, a total distance of 81.4 NM. I would have been out of the service volume for 1.4NM and ATC would not give me that clearance. Go figure.

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  • $\begingroup$ On your TUS to IWA flight, if your aircraft is GNSS equipped, direct point-to-point is no problem. If it's /A, I would issue KTUS.V16.TOTEC..IWA..KIWA, then give you a vector to IWA VOR when I had you in radar. $\endgroup$
    – atc_ceedee
    May 5 at 16:09
  • $\begingroup$ @atc_ceedee. They issue V105 because V105 is used for flights from PHX to TUS. I agree with your comment and makes complete sense. Welcome to the forum. Your knowledge is quite valuable here. $\endgroup$
    – wbeard52
    May 5 at 16:52
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    $\begingroup$ Ah, that makes sense. As far as the communication issue goes, though, ATC should issue lost comm instructions (although, I admit it's nearly a lost art) for any clearance where an aircraft may enter areas of poor communication. The onus there is on the controller (we're supposed to know our frequency coverage), but that's poor consolation if you find yourself out of comm range and in trouble. $\endgroup$
    – atc_ceedee
    May 5 at 17:47
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You may file a direct route with no more than a radio, and by doing so, you're telling the controller that you can actually fly it.

Controllers have their own rules, though, which are there to protect you and the FAA.

For example, if your aircraft is /X equipped, and you file a route beyond navaid limitations, it's my responsibility to ensure that you are cleared on a route that meets those limitations. There is no gray area.

(Oddly, a Center controller can use anticipated radar coverage for separation, but not for eliminating navaid limitations. Maybe terminal has a rule they can use.)

Once you're in radar contact, however, I can clear you direct to your destination, and radar monitor your flight (generally, I'll clear you direct the navaid that services the airport). If you get off course, I can then provide navigational assistance (vectors) to get you back on course.

You may also file OTP (VFR on top), and receive clearance beyond navaid limitations, without the necessity of being in radar coverage. For my part, if you are out of radar coverage, I'll ask for position reports every so often, to make sure we're still in contact, and that you're still alive and kicking.

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    $\begingroup$ Since you are a retired controller, I wonder if you would have anything to say about these questions -- , aviation.stackexchange.com/questions/64205/…? , aviation.stackexchange.com/questions/48106/… . Btw, I now consider my answer to the second one to be in need of a great deal of revision.Here's another related one-- aviation.stackexchange.com/questions/49063/… $\endgroup$ May 4 at 16:05
  • $\begingroup$ Regarding "SVFR and class E extensions", Center is required to keep all IFR and other SVFR aircraft clear of the entire Class E area for the airport until the SVFR with clearance is either on the ground or clear of the surface area. If you need the airspace, you have it. In the case of Class D, the tower must be coordinated with (usually, THEY make the call, but someone has to) and then the clearance may be issued. We will issue altitude based restrictions if necessary (at or below ALTITUDE while in Class E...) to separate from IFR traffic. $\endgroup$
    – atc_ceedee
    May 4 at 16:56
  • $\begingroup$ Regarding "weather report in Class D controlling Class E extension", I think pondlife's answer is great. If, for instance, an aircraft wants to traverse the area in SVFR conditions, I'd allow it based on the weather, if it meets SVFR minima. If the weather is below those minima, I'll ask the pilot about his flight conditions, and to say intentions. If the airport is busy, I will probably deny clearance. They should go around. If, however, the pilot elects to go THROUGH the area anyway (and I don't know which target he is), there's not much I can do except traffic advisories to other aircraft. $\endgroup$
    – atc_ceedee
    May 4 at 17:06
  • $\begingroup$ A good example, on the Cheyenne sectional chart, would be STK and AKO airports, which have surface areas that overlap. If an aircraft requests SVFR into KSTK, and I issue it, I'll protect that KAKO area, as well. In this instance, it's very unlikely (based on normal traffic) that these two airports would be active at the same time, anyway. $\endgroup$
    – atc_ceedee
    May 4 at 17:13
  • $\begingroup$ The requirements for SVFR constrain the controller to protect the entire area because the aircraft must maintain visibility and clear of clouds minima. I don't know what the pilot must do in a given situation to accomplish that. That is why we sterilize the airspace when we clear SVFR. Conversely, I can clear two IFR aircraft into/out of/through Class E areas, because I can constrain them to headings, radials, courses and altitudes, etc. $\endgroup$
    – atc_ceedee
    May 4 at 17:22

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