At the risk of wearing the topic out, I'll wade in here again. We've had this conversation before here, I believe... I'll preface my remarks by saying this is one of those "detail items" which rarely if ever comes up on an instrument rating practical test. I'm sometimes amused at the level of evaluatory detail which some pilots think is being applied to this rating. It's not an ATP checkride, folks! It's an added rating to a private pilot certificate in almost every feasible instance. I'll also state for the record that I think this is one of those situations which rarely, if ever, really makes a difference in the real world.
Couple of caveats - mandatory or "hard" altitudes published on an instrument approach procedure must be adhered to, so that's not what we're discussing here. And an ATC instruction to intercept the localizer at an altitude below a published minimum altitude segment on the approach is also outside the purview. Not looking to make this extraordinarily nitpicky -- we all understand the concept at play here, which is whether or not the pilot should/could/must descend to intercept the glideslope at the published GSIA (Glide slope intercept altitude) under "normal" circumstances.
The first (and for some reason, possibly contentious) fact of the matter is that intercepting the glideslope at the published Glideslope Intercept Altitude is, in fact, the
recommendation of the day per the FAA. Not sure why that's been debated (or may be debated here) but it's pretty straightforward, in black and white, in the AIM. We can debate whether it's a good recommendation or not, we can debate just how much "weight" the AIM has in these situations, and all of those kinds of things, but we can't really debate what the AIM says. At least not with a straight face. This is found in AIM 5-4-5, Instrument Approach Procedure (IAP) Charts.
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To understand why this guidance came about, look back roughly 9 years ago. This was due primarily to the LAX approaches. Here's the story from that time.
https://nbaa.org/aircraft-operation...ance-on-instrument-landing-system-intercepts/
Since then, there's been some movement on the issue, and it's not as much of a problem nowadays, particularly at LAX. I remember when it was new guidance because I went to FSI for a Hawker recurrent and the hot topic at the time was not joining an ILS glideslope outside of the FAF. Since then that sort of drifted out of FSI's sphere of consciousness. But the guidance in the AIM remains. It gives the pilot some latitude; you
may "[choose] to track the glide slope prior to the glide slope intercept altitude, [but you] remain responsible for complying with published altitudes for any preceding stepdown fixes encountered during the subsequent descent."
The last time we went around on this, that was the remark which led some to believe they could wash their hands of the matter and do as they please. I recall reading some comments along the lines of "gee, why can't I intercept the glideslope while I'm already on the glideslope crossing the localizer-only FAF" and other sorts of relatively 'cute' attempts to re-imagine this guidance. Yeah, no. The AIM is quite clear on this. It's not mandatory, but it's clear guidance. That being said, look at it from an ADM and RM perspective, which is a big part of the instrument rating practical test.
Scenario: applicant is assigned an ILS with stepdown fixes. They are either vectored in, or given "direct to" a point on the approach which includes step-down fixes ("at or above" altitudes only). They choose to join the glideslope a couple of fixes out -- say 8nm or so from the published GSIA (which is the FAF.) They use their Garmin 430W "vectors to final" mode and don't appear to be aware of any minimum altitude stepdowns, assuming the glideslope is "good enough." How does an evaluator handle this? How about a couple of questions -- "what would you do if the glideslope failed right now?" "Where would you initiate your descent, and to what altitude?" If the applicant is fumbling around trying to figure this out while hand-flying the approach under a view-limiting device, possibly trying to do some mental math, the question could also be asked "why'd you join the glideslope here instead of descending to the minimum published altitude for this segment?" Basically, none of it is all too good of a "look" for an applicant who is flying contrary to guidance and finds themselves in a pickle as an indirect result of it.
And of course it begs the question, why go against the guidance. That would be very difficult for an applicant to answer if pressed.
Now... let's be clear here... this has never come up on any of my instrument rating practical tests, and probably never will. But it's a nice little example of how published guidance should just be accepted for what it is, published guidance. It's not mandatory, and it may even be a little out of date, but you likely don't want to be in a position in which you have to explain why you're acting contrary to it on a practical test.
