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6 Answers

Inoperative Glide Slope on ILS Approach

Asked by: 6483 views , ,
FAA Regulations, Instrument Rating

OK...  I have a nagging question that I can't figure out.  I don't know if I just haven't found the answer yet or if it was a bad design by the FAA.  I've read the TERPS criteria as well as how the pilot is supposed to comply with the approach plate.  I also realize that we are talking about worst case scenarios and the likely hood of this scenario playing out is slim.


The question is what happens if I am flying a ILS (no LOC mins) only approach inside the Final Approach Fix and the glide slope fails?  The obvious answer is to get radar vectors to another approach.  As good instrument pilots we are taught to plan as though there are no radar services.


So the scenario is you are cleared for the Van Nuys ILS Rwy 16R approach proceed direct Fillmore maintain 6000 cleared approach.  On the way over, a power failure knocks SOCAL approach radar out.  As we proceed inbound, the glideslope on our receiver fails inside the FAF.  To say the least, the marine layer has the approach below minimums.


Where is the missed approach point?  Typically, the missed approach point is the decision altitude on the glide slope but we can't ideitify the MAP?  Would you turn early on the missed approach course? Climb on the final course, keep descending?  How can we comply with the TERPS design if we can't positively identify the missed approach point?


Other approaches to consider:

Reno ILS 16R

Washington Int'l ILS 15R


Thanks for pondering this question with me.

6 Answers

  1. Steve Pomroy on Feb 18, 2011

    Hi Wesley.
    The Decision Altitude is the minimum altitude at which you can decide to initiate a missed approach.  Similarly, the MAP is the latest point at which you can initiate the missed approach.  There is nothing stopping you from initiating a missed early.  In the example in question (glideslope failure), I would say initiate the missed upon recognition of the failure, and fly the missed as published.  The approach design standards as I understand them allow for an early missed approach, but not a late one.

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  2. John D. Collins on Feb 18, 2011

    I would suggest you initiate your climb as soon as possible and determine the MAP using other means, such as timing, GPS, DME or VOR To/From passage.  At the MAP and at or above the appropriate altitude, begin any required turn.
    Steve, from the AIM section “5-4-21 Missed Approach”, at the end of paragraph b.:

    “Reasonable buffers are provided for normal maneuvers. However, no consideration is given to an abnormally early turn. Therefore, when an early missed approach is executed, pilots should, unless otherwise cleared by ATC, fly the IAP as specified on the approach plate to the missed approach point at or above the MDA or DH before executing a turning maneuver.”

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  3. Kent Shook on Feb 19, 2011

    That’s an interesting approach, Wesley.
    First thing I noticed: Where’s the PT? No depiction for it, no NoPT marking… And then I realized that those are actually procedure tracks leading from both VOR’s. Pretty unusual. Also pretty irrelevant to the question. 😉
    The next issue in this case is that the missed approach includes a restriction to cross 1.5 DME south of VNY at or below 1750 MSL prior to beginning a climbing left turn to 4000 to hold. So, the initial reaction I had (John too) to “climb right away” wouldn’t work unless the glideslope failed very close in. Presumably this is because there is potentially conflicting traffic on another procedure over the top of VNY going somewhere else. We don’t want to hit them, but… How do we descend to avoid that traffic, while also avoiding terrain? There are no localizer mins to descend to.
    In this case, there really is not a good solution to the problem as given. If I ended up in this “doomsday scenario” however, I think I would continue at the same descent rate to 1750, and use DME and/or the radials off FIM to ascertain my distance from the VNY VOR to attempt to double-check that I wasn’t descending below glideslope. Not a great solution, though.
    The BWI one is the most straightforward of the three: Climb right away, cross the VOR, follow the procedure. The RNO one, climb right away, and upon reaching a safe altitude turn to the VOR and follow the procedure. Holy cow, those are high minimums! 2031 AGL on an ILS!

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  4. Wesley Beard on Feb 20, 2011

    I’ve read in both the AIM and Instrument Procedures Handbook that an early missed approach turn is not advised.  In KTUS, on the VOR or ILS 11L a early right hand turn will send you right into the side of the mountain.
    I’ve read the missed approach procedures for the ones I linked and the Reno one is really what interests me.  Then the question becomes on when to turn?  There is no DME, or VOR radial that we can use to help us in our decision.  We can use a GPS but that doesn’t work for every airplane.  If our radio still works, we can call the approach controller to see if we can turn early through their MVA.
    Perhaps a more thorough study of these approaches is required for this slim scenario.  I am guessing we can talk about what happens if the VOR fails on a VOR approach or the localizer fails on a LOC / ILS approach.
    Thanks for your responses.

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  5. kevin on Jan 26, 2013

    To answer this question appropriately, there is a regulation in the AIM. 1-1-9, subcategory J, under “Inoperative ILS components!!!!!!!. I can’t believe these so called cfi’s that dont know where to find this!!!!!!!!. The answer is ” The ils reverts to a non precision localizer approach.”
    It doesn’t mean that it’s safe though!!!

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  6. Wes Beard on Jan 27, 2013

    Kevin, The attached approaches due not have localizer minimums. How can we revert to a localizer approach with a defined approach?

    The question is where is the MAP when you can’t determine the DA and the approach does not include localizer minimums?

    Knowing Terps requirements to not turn before hitting the MAP leads me to figure out this question.

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