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23 Answers

VOR Approaches

Asked by: 13769 views General Aviation

CAN YOU OVERLAY A VOR APPROACH?

THANKS

 

23 Answers



  1. Wes Beard on Feb 01, 2014

    If the approach states “VOR 14” and not “VOR or GPS 14” then the answer is maybe.

    Most operators are required to have the navgational source up that defines the final approach course and in the case of “VOR 14” only that navigational source is a VOR. Most operators will also let the FMS or GPS fly the approach with a bearing pointer showing the VOR navigation source. The crew will monitor the bearing pointer to ensure the FMS or GPS is going where it is supposed to go.

    If you cannot display the nav source somewhere then you must use it as your primary navigation.

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  2. John D Collins on Feb 02, 2014

    The operators Wes is referring to are generally airlines and each operator must be specifically approved by the FAA for this capability. For us part 91 operators, we are not approved and may not fly a VOR approach using the GPS unless it includes GPS in the approach title.

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  3. Wes Beard on Feb 02, 2014

    I fly with a lot of Part 91 corporate pilots who use the procedure I detailed above. Even the FAA personnel we talk to use this procedure. You must have a bearing pointer up showing you the VOR though.

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  4. John D Collins on Feb 02, 2014

    Wes, part 91 operators have to comply with AC 90-108 for their primary navigation for the final approach segment on a VOR approach that doesn’t have a GPS overlay. The procedure you described is OK as long as the primary navigation is via the VOR.

    For other approved operators, they can use their RNAV systems as the primary navigation source IAW OpSpec C300. It permits: The certificate holder is authorized to conduct NDB, NDB/DME, VOR, and VOR/DME IAPs using the procedures described herein. This operations specification applies when the underlying navigation aid (NDB, VOR, or DME) is out-of-service and/or compatible aircraft avionics is either not installed (automatic direction finder (ADF) or DME) or not operational (VOR, ADF, or DME).

    AC 90-108 applies to part 91 operators and has the following limitations:

    8. USES OF SUITABLE RNAV SYSTEMS NOT ALLOWED BY THIS AC. An otherwise
    suitable RNAV system cannot be used for the following:
    a. NOTAMed Procedures. Unless otherwise specified, navigation on procedures that are identified as not authorized (“NA”) without exception by a NOTAM. For example, an operator may not use a RNAV system to navigate on a procedure affected by an expired or unsatisfactory flight inspection, or a procedure that is based upon a recently decommissioned NAVAID.
    b. Substitution on a Final Approach Segment. Substitution for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment.
    c. Lateral Navigation on LOC-Based Courses. Lateral navigation on LOC-based courses (including LOC back-course guidance) without reference to raw LOC data.

    My point is there are two sets of rules, one for the airlines and one for part 91.

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  5. Wes Beard on Feb 02, 2014

    John,
    I understand what the AC states. I also see the point that you are trying to make. I read the AC differently. It says in Part B that we cannot substitute a VOR or NDB for the final approach segment and I agree. The AC does not state that it has to on the primary source. Many Part 91 operators will monitor the VOR or NDB on the bearing pointer to ensure they stay within the final approach segment.

    In essence, the autopilot is following the GPS or FMS and we are ensuring the aircraft stays within the final approach segment by monitoring the bearing pointer. It is really easy to see if they disagree.

    I don’t fly for the airlines but have quite a bit of experience on what the common practices are for Part 91 and 135 operators.

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  6. John D Collins on Feb 02, 2014

    Primary source doesn’t mean a particular system such as what your #1 HSI is displaying or how the autopilot is controlling the path. It means that the navigation source that gets the final vote. If you are monitoring your bearing pointer from the VOR and it doesn’t agree you are on course, then you have to adjust your course. The bearing pointer is your primary source for the VOR and it gets the final vote.

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  7. Kris Kortokrax on Feb 02, 2014

    John,

    You can lead a horse to water. You can force its head underwater, but you can’t make it drink.

    In spite of language in the AIM and TERPS (which is incorporated into Part 97 by reference) which states that the equipment named in the title of the procedure must be used for guidance on the final approach segment, it appears there are those who chose to ignore it.

    Another note about C300. It is not available to part 91 operations. Further it does not allow one to fly a procedure as an overlay at will. Each procedure to be flown using RNAV must be flight checked prior to use and every time the lateral course changes.

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  8. Wes Beard on Feb 02, 2014

    Thanks John. That is what I’ve been saying all along. We monitor the bearing pointer and if it doesn’t agree with the GPS we have to make a course change.

    Kris, I found your remarks rude and provide nothing to the discussion. We have always had the primary navaid displayed somewhere in view of the pilot.

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  9. Mark Kolber on Feb 03, 2014

    Wes, I think Kris’ qualm is that from a teaching standpoint (and to continue his horse allusion 😉 ), if not putting the cart before the horse, your description at least mixes the two. What you describe is pretty much how I flew NDB approaches once I had access to a handheld aviation GPS. I would look for agreement between the two, but within a tolerance level based on an expectation that the GPS would be far more accurate than the ADF.

    Although the handheld uses different rules than a panel-mount, IFR-certified TSO’d unit, I think the comparison is useful because, in both situations, one unit is being used for “primary navigation” and the other for “situational awareness.”

    The question is how to describe it from the FAA’s differentiation, and I’m not sure that “we fly the GPS and monitor the bearing pointer” accomplishes that. Sounds more like the GPS is primary and the VOR is for situational awareness.

    Truthfully, with both in cockpit and in view of the pilot, it probably doesn’t make a difference in operation. And the difference between “primary” and “situational awareness” is at least as muddy as “primary and supporting” instruments. But strictly from a teaching standpoint I’m not sure that feeding the primary flight instrument (HSI) with the GPS feed while monitoring the VLOC on the side (even with the “final word”) is the best way to describe the process.

    I’m trying to picture an instrument checkride with the applicant not changing the CDI source for the HSI or the NAV-1 OBS (as applicable) and explaining to the DPE , “well, I have the ILS tuned in on NAV-2 so it’s ok.” I don’t see anything good.

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  10. Wes Beard on Feb 04, 2014

    Mark,
    I agree with you that this method is more advanced and instrument students should not use it. I certainly would not allow my students to use it till they were quite proficient. But the question wasn’t dealing with an instrument student but in general. Had the original poster said instrument student my answer would have been different.

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  11. Mark Kolber on Feb 05, 2014

    Wes, Since the name of the forum is “Ask a Flight Instructor” I start with the assumption that every question is from a student perspective.

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  12. Kris Kortokrax on Feb 06, 2014

    Wes,

    91.174 (a) states “Unless otherwise authorized by the FAA, when it is necessary to use an instrument approach to a civil airport, each person operating an aircraft must use a standard instrument approach procedure prescribed in part 97 of this chapter for that airport.”

    97.20 (b) states “Standard instrument approach procedures and associated supporting data adopted by the FAA are documented on FAA Forms 8260-3, 8260-4, 8260-5. Takeoff minimums and obstacle departure procedures (ODPs) are documented on FAA Form 8260-15A. These forms are incorporated by reference.” They become part of Part 97.

    Order 8260.3B (TERPS) states: “Instrument procedures that meet criteria for authorization of straight-in landing minima shall be identified by a prefix describing the navigational system providing the final approach guidance and the runway to which the final approach course is aligned”

    If you fly a VOR procedure and do not use the VOR signal for final approach guidance (feeding the NAV signal to the autopilot or hand flying the approach with reference to the VOR CDI), you are breaking a regulation. The VOR signal is primary. The RNAV may certainly be used for situational awareness.

    No reputable school would teach your “advanced method”. You will not learn it as a normal procedure at FlightSafety, Simuflite, Simcom, Bombardier or any other Part 142 training center.

    As far as rudeness goes, I consider the condescension in your replies to John to be rude. He attempted to correct your misinformation and you reply with patronizing comments that it is an “advanced method” that your Part 91 pilots and some unnamed FAA personnel use. I would love to see anything in writing from an FAA inspector advocating your technique.

    Mark,

    Yes, it’s really disconcerting to see info like that show up on a site frequented by students. It is just as disturbing to see it suggested to experienced pilots as a valid technique.

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  13. Kris Kortokrax on Feb 07, 2014

    Wes,

    I thought a bit about the 142 training. I would amend my statement to agree that the 142 training centers would indeed train substituting RNAV for a VOR or NDB if your 135 or 121 operation has OpSpec C300.

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  14. tommytom on Feb 08, 2014

    So in plain language – It’s ok for Part 121 and 135 operators to sub rnav for VOR, ndb, etc. But do not teach my students this practice.

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  15. Kris Kortokrax on Feb 09, 2014

    Not quite Tommy.

    Part 121 and 135 operators may only substitute RNAV for VOR or NDB if they have OpSpec C300. I would bet that there are only a handful of operators who have this OpSpec.

    Absolutely, do not teach your students this practice, as it is contrary to regulation.

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  16. Wes Beard on Feb 09, 2014

    Kristian,

    I think we can all agree that for initial instrument students we should teach them to only use the nav source mentioned on the chart. As they get more experience and understanding of the national airspace system we can teach some advanced techniques that comply with the regulations. I’ve been to many 142 training events and this is where I learned this technique. I would imagine that some teach one way the advanced way and others do not.

    I am not trying to be rude but I have read the regulations you posted and do not agree with your wording “(feeding the NAV signal to the autopilot or hand flying the approach with reference to the VOR CDI)” that I am breaking the regulations. The order you mentioned says nothing about making the autopilot/flight director follow that nav signal. If that was so, how would anyone with an autopilot/flight director fly an NDB approach since there are no, maybe only a few, airplanes whose autopilot/flight director will follow such a nav source? The pilot is required to have the navigational source available to the pilot and they must be monitoring that navigational source. If the GPS/FMS disagrees with the guidance from that nav source the pilot must follow the nav source listed on the approach plate. But we said that already so there is nothing new here. This is a technique and you can choose to use it or not; that is your choice. I can lead you to water but choose not to dunk your head under it. That would be rude.

    Like I said, this is the method that jet pilots use and were most likely taught at a 142 school. The original questions: “Can you overlay a VOR approach?” is absolutely with some added workload on the pilots as previously discussed. Is it a good idea for brand new instrument students… No. but then again the question didn’t specify that. Don’t you all think that professional pilots still get training from flight instructors? The site is called “Ask a private, instrument or commercial flight instructor”.

    We all said what we think and can consider the topic closed.

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  17. Kris Kortokrax on Feb 09, 2014

    Wes,

    I can understand that you might not want to beat a dead horse (to continue the equine metaphor). I think the horse has a couple of breaths left.

    For instance, If we accept your premise that anyone may fly any VOR approach as an overlay, why would there be a need for OpSpec C300?

    Why would one choose to feed a Nav signal from the RNAV to an autopilot and then add to his workload by monitoring an RMI for the VOR, instead of selecting the VOR signal for the autopilot and let it follow that signal? How is this considered an “advanced technique”?

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  18. Wes Beard on Feb 10, 2014

    From my understanding OpsSpecs C300 allows one to use a RNAV receiver in lieu of the nav signal on the chart. So there would be no need to bring up a bearing pointer. As a result, there is also no need for the underlying navaids to even be operational. Kris, this is a very good question.

    See this memo from the FAA: http://www.faa.gov/documentLibrary/media/Notice/N%208900.150.pdf

    Why would one choose to feed a Nav signal from the RNAV to an autopilot and then add to his workload by monitoring an RMI for the VOR?

    Most of the jets that I have flown do not do a decent job of flying a VOR signal when inside the cone of confusion. Most autopilots have a certain time frame they will be in “dead reckoning” mode and then turn to re-intercept the course. This causes the aircraft to S-TURN on final which isn’t really comfortable for the pilots or the passengers. Others may place the aircraft in HDG mode while over the cone of confusion and wait for the nav CDI to come back to the middle. This method may not automatically recapture the VOR signal and the HDG bug has to be moved to try and force the flight director to recapture the signal thus adding workload to the pilot. Those that use the RNAV technique do not have these issues.

    To recap for jet pilots there are three techniques that are commonly used:
    1. Autopilot capture to the VOR signal… over the cone of confusion the autopilot will turn to try to automatically recapture the signal making it uncomfortable for the passengers.
    2. Autopilot capture to the VOR signal… over the cone of confusion place the autopilot into HDG mode. The VOR may not recapture and the pilot will have to manually try and recapture the nav signal.
    3. Fly the approach using the GPS/FMS, when over the cone of confusion do nothing but monitor the RMI. There are no turns and no uncomfort for the passengers. More vigilance is needed to ensure the aircraft stays within the final approach corridor.

    There are benefits and issues with each method… not to mention that the pilots usually have to descend from the VOR inbound at 130+ knots IAS. I really hope this answers why some prefer the “advanced technique” method.

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  19. Keith Andrews on Mar 25, 2014

    There is a lot of solid information being discussed here. I think John pretty much nailed it with his reference to AC 90-108. I just want to add this to your conversation as some of the information references part 91 operators is. This is not meant in anyway to confuse student pilots. I only add my post to share some knowledge.

    As a part 91 operator flying a Gulfstream 550 we do fly VOR approaches using our FMS system. We don’t do that because we don’t care about regs or it is an advanced technique. We do it because the FAA has certified our avionics suite to be able to do it. Our FMS system identifies and monitors the VOR associated with the approach selected in the FMS. It will flag the approach if the VOR signal is lost, just as if we were using raw VOR needles. So we can and are trained by FlightSafety to fly a VOR in FMS mode with out displaying those navaids because our FMS is certified for use that way. This is a very specific example I know but I thought some might find it interesting.

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  20. Austin on Jul 12, 2014

    I think the mistake many are making is to use a layman’s definition of “substitute” ,,, Read the ENTIRE AC folks, don’t skim it…. There is a difference defined between a substitute and an alternate means of navigation defined within the AC.

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  21. Wes Beard on Feb 27, 2017

    This is a follow-up to the question. The answer is now absolutely YES!. However, as previously stated, I would not teach or allow my students to use the GPS as an overlay for initial training. The FAA has now explicitly allowed the use of the FMS along the final approach segment (FAS). The reference is found in 91-1088 and the new piece in AIM 1-2-3(c) Note #5.

    This note quoted: “5. Use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure based on a VOR, TACAN or NDB signal, is allowable. The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment.”

    So therefore, I allow the FMS which is connected to the flight director / autopilot fly the approach and I monitor the VOR or NDB with a separate HSI, receiver or bearing pointer. Wherever the VOR or NDB needle goes, I MUST follow inside the final approach fix. I don’t know about you but I am not prepared to continue an approach where my navigational aids differ; so I choose to go missed at which time I am now allowed to use the GPS as my “alternate means of navigation”. I then find a different approach to fly or go to my alternate airport.

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  22. John D Collins on Feb 28, 2017

    Wes,

    Please note that the AIM guidance is a clarification and not an actual FAA change in policy. I participated in the ACF discussions on this topic (ACF-IPG recommendation 14-02-317) . The Opspec allows the operator to use the FMS and not depend in any way on an operating VOR or have to display the raw VOR data as primary guidance on the final approach segment. The Aim update (AC 90-108 will have the requirement reworded to match the AIM in a future update) includes the wording in the note: \”The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment\”. These limitations are distinctly different than the Opspec C300 which states the following limitation: \”This operations specification applies when the underlying Navigational Aid (NAVAID) (NDB, VOR, or DME) is out of service, and/or compatible aircraft avionics are either not installed (automatic direction finder (ADF) or DME) or not operational (VOR, ADF, or DME).\”

    So in summary, with the AIM guidance, part 91 operators must have the VOR installed, operating and monitored for course deviations on a CDI or RMI type indicator, and the VOR station must be operating. That is another way of saying the VOR indication is primary and can\’t be substituted for. This is \”minor word changes\”, see the notes of the meeting where this was agreed to.

    MEETING 15-02: Kel Christianson, AFS-470, said currently we have substitute and
    alternate navigation with RNAV systems on conventional procedures up to the FAF, but
    it is not authorized inside the FAF, and these two do not require the pilot to monitor a
    NAVAID. Draft explanatory AIM language including a note (View) was shown. Lev
    Prichard, APA, said airlines under OpsSpec approval can directly substitute with suitable
    RNAV inside the FAF, but no one else can. Kel said C300 allows this currently (part 121
    and some other operators can get this), but in general, aircraft cannot proceed inside
    FAF without monitoring the ground based navigation system. Rich Boll, NBAA, asked if
    once this is in the AIM, does it cancel the OpsSpec? Kel said no, adding without the
    provisions of OpsSpec C300, the underlying ground system must be operational and
    received in aircraft to ensure course alignment. Kel said this is a change, even though
    some pilots are incorrectly doing it now anyway. Larry Hills, FedEx, inquired if this
    language should be tightened up to refer to the NAS only, and Kel concurred. Jeff Kerr,
    AFS-470, explained the main point in OpsSpec C300 is that the airline is required to
    check flyability on the final approach segment. In the absence of C300 authorization, you
    must be able to monitor the underlying ground navigation system for course alignment.
    Lev commented about the confusion on this, and Kel added AC 90-108 explains the
    terms. Kel will make some minor word changes and keep the agenda item open until the
    AIM is published.

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  23. Wes Beard on Mar 01, 2017

    John,
    I agree with you completely. We are saying the same thing.

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