"If you're asking if you can, the answer is yes. If you're asking if you should, that's a different story" - Dr. Tizi
Question:
If I am cleared for an ILS approach and during the final approach segment I lose my glide slope (GS), can I continue the approach and fly localizer (LOC) minimums to Minimum Descent Altitude (MDA)?
Answer:
YES
This question was asked by my friend Josh who just wanted a sanity check prior to a checkride. The answer is simple, yes you can!
However, in searching for the correct reference online, I stumbled upon many different pilots offering their opinions. Generally, I love opinions because they make me think. In this case, though, it can confuse a student on what is regulatory vs. a pilot's personal opinion. Since I got frustrated searching for a regulatory answer and only got "Well, what I would do" type of answers (many of which claimed a non-existing authority or knowledge...), I thought of reporting the guidance here.... once and for all!
Ok, here we go.
What the "OR" on the chart means
The ILS approach chart is actually called "ILS OR LOC". LOC is in fact another line of minima, and the pilot can select what minimums they wish to execute. Just like an LPV vs. LNAV/VNAV, etc. The AIM is prescriptive about this in 5-4-5(a)3(a): [...] more than one navigational system separated by the word "or" indicates either type of equipment may be used to execute the final approach.
So... you can use either ILS (which is LOC + GS) ... or the LOC (which is... well, just the LOC).
ILS with broken GS = LOC!
Per AIM 1-1-9(j), [...] when the glide slope fails, the ILS reverts to a non-precision localizer approach. Ok, that's kind of dry, but, there you go. If the GS breaks, the published procedure in its existence becomes another one, already defined in the same chart.
ATC's side of things
ATC does not police minimums. That is not to say that you can do "whatever you want" cause they won't see. There are automated low altitude alerts which they can't ignore, and you should NEVER attempt to go below minimums without appropriate runway environment in sight (and ALS, yeah yeah yeah) thinking that ATC can't see you. They are a friend and a resource, so act accordingly like a true professional. Guidance to ATC is covered in 7110.65 Section 4-8-1(a)1 and 2. The document says two interesting things:
ATC needs to ammend the clearance if they want you to execute a specific procedure when more than one is published on a single chart. That is found in (a)1.
ATC does not need to advise you that the GS is inoperative, if the title of the procedure offers an alternative. That is in (a)2. Interesting, huh?
So yeah, if they want you to specifically fly the ILS and not the LOC, they need to tell you in their clearance.
Report it!
Would we call losing the GS a safety-critical event? Absolutely! That is why AIM 5-3-3(h) indicates that the loss of navigational equipment, including the GS, should be reported at all times. I mean, why wouldn't you?
Shall vs. Should
Ok, now we get to your all-knowing opinions, my beloved keyboard lions (that is an Italian expression for those who have plenty of courage with a keyboard but are more like Courage the Cowardly Dog when faced in person, but you probably don't care about this... unless you were wondering why I would ever say that expression. In that case, there's your answer. And, if you don't know who Courage the Cowardly Dog is...).
The AIM is not a regulatory document. It's advice. Strong advice. The AIM is designed to provide clarification and advice to conduct a safe flight. In the certification world (where I work), we say that the AIM provides us with "should" and not a "shall". Regulations tell you that "you shall do or not do this", while the AIM limits you to "you should do or not do this".
Here are a few themes to consider if you should continue the approach with LOC minimums:
Are you able to identify the Missed Approach Point (MAP)? Did you need to start a timer at the FAF to identify your MAP? Do you have alternative equipment that can give you the MAP? Maybe GPS? Have you ever considered this question before?
Are you above or below the LOC MDA? If you're below the LOC MDA, there is no alternative and you have to go missed. If you're above the LOC MDA, do you have time to arrest the descent and not go below MDA?
Do you feel comfortable? Losing a GS is not a calming event... Going through my mind would be the question "why did the GS fail"? Is it the antenna on the ground? Is it the aircraft's antenna? Are things happening too fast? Personally, if I were in IMC, I think I'd go missed and revert to a different navigation equipment.
Does your operation and operator manual allow you to do this? No, I'm not talking about the POH. I'm talking about whether you are flying under Part 91, 135, or for an airline. If your airline SOPs say to go missed if the GS fails, good for you, but that does not apply to the rest of us little Piper pilots.
Oh, and there's an FAA question about this, too.
Immediately after passing the final approach fix in bound during an ILS approach in IFR conditions, the glide slope warning flag appears. The pilot is:
A) Permitted to continue the approach and descend to the localizer MDA.
B) Permitted to continue the approach and descend to the DH.
C) Required to immediately begin the prescribed missed approach procedure.
If you're curious, the reference points at 1-1-9(j)... yup...
In Conclusion....
If you lose the glideslope during an ILS approach, whether before or after the FAF, you can continue the approach, switch to LOC minimums, if the conditions to do so exist.
Note: This article was reviewed for accuracy by an experienced pilot instructor and air traffic controller. Thank you, Dr. Bill and AF!
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