Intercepting ILS final approach course, do I have to descend right away?

That’s 25L, not R. You should be good at GATTE on a Standard or colder day, but if it’s much warmer, the Glideslope could take you lower. HUNDA could be a bust on a cooler day. Not by much, were talkin maybe 50 feet or so. Unless it’s real hot out, then it could be significant enough to be detectable on MODE C read outs, which work in 100 foot increments.

 

And yet the LAX ILS 25L has you navigating by the localizer all the way in from 37.2 DME.

Service volumes only apply when you are not on a published route. My understanding is that charted routes are flight checked throughout.

 

MODE C read outs are considered valid up to +/- 200 feet by ATC. So the variations were talking about here are not going to be significant enough to cause a loss of separation and cause a ‘bust.’ After the last ‘step down’ fix, you don’t have to comply with FAF altitude if you are on Glidepath. This close in, ATC is not going to have traffic under you that will cause a Separation problem. It’s farther out at higher altitudes where the separation problems were happening.

 

Absolutely. Typo on my part. Thanks. Same issue applies to both runways.

 

Not by ATC.

 

That raises an interesting question relative to Clip4's point about the instrument ACS: Has anyone busted a checkride by delaying the final stepdown descent until the glideslope is intercepted?

 

That's why I said, "Not by ATC." Pilots have been busted many times when the DPE was wrong. Fortunately, not so at the major airlines because of standards and a union watchdog committee.

 

For the original question, it depends on your clearance.

If ATC says, "Maintain 3,000' until established..." then, once established you can descend based on the charted procedure. If you're on a segment that is charted as at-or-above 2,000' then you don't have to descend yet.

If you are at 3,000' and ATC says, "Maintain 2,000' until established..." then you must descend to 2,000' now.

If you are at 3,000' and ATC says, "Maintain at or above 2,000' until established..." then you maintain at-or-above 2,000' until required to descend further by the procedure.

Altimeter and Mode C tolerances are not buffer that can be used by the pilot as he sees fit. The assigned, and published, altitudes on the procedure, were established so that these inherent equipment inaccuracies would not compromise traffic or terrain separation. That doesn't change, no matter how many compliments you may have received on your instrument's accuracy.

 

Why argue? It's like any other checkride activity. Despite the uniformity of the ACS, DPEs have their own proclivity and biases. If you happen to have DPE who thinks "at or above" means a hard "at," (or for that matter that you'd better not turn an extra 30° to do a teardrop rather than parallel hold entry) learn that in advance. Do what the DPE wants and forget about it after you pass. Easy peasy.

 

Yes. Not me. But I was in a discussion about one where I knew all the players.

 

This is correct. Any published route (enroute, approach, departure, arrival, etc.) that extends beyond the standard service volume of a NAVAID will have been evaluated for signal strength (etc.) in a process called an "Expanded Service Volume". You can bet those ILS's at LAX have been.

 

Do you happen to know what legal reasoning was given by the FAA, ALJ, or whoever for deeming it to be a violation?

 

True. I wasn’t implying that pilots could. I was responding to the question ‘have there been any ‘busts’’ The +/- 200 foot tolerance will stop an official ‘loss of separation’ from being processed as a Pilot Deviation.

 

Sice the reference was to the instrument ACS, I thought that tangent was about busting a checkride. No, I am aware of no one who has been violated solely for obeying a charted altitude.

 

Maybe, unless ATC says "Say altitude" and the pilot responds with what his displayed on his altimeter.

 

Confession is not always good for the soul

 

Some do. Some have higher-powered antennas and are certified farther than 18nm. A lot of big airports with parallel or PRM type approaches have localizer service volumes of 25 miles or more.

 

At most of the big airports, a base turn within 18nm would be a short approach!

 

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.



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.

 

As a CFI you supposed to teach proper procedures, including “guidance”. Much of what we teach is guidance that is neither contained in the regs or required on a practical test.

 

That AIM paragraph clarifies things greatly.

While intercepting the glideslope at the depicted altitude is the AIM-recommended way, the last sentence of that paragraph clearly implies that the pilot has the option of following the glideslope sooner if none of the preceding minimum altitudes are violated. That requirement is why I have been talking about following the glideslope AFTER passing the last stepdown fix.

PRIOR to that fix, following the glideslope adds to the workload, because on an ILS like the ones at LAX, it means that you're simultaneously tracking the glideslope AND monitoring all those stepdown altitudes. For me, doing one thing at a time reduces my chances of making a mistake, which means that before the last stepdown fix, my preference is to ignore the glideslope and concentrate on descending at the specified fixes and leveling off at the specified altitudes.

AFTER the last stepdown fix, following the glideslope will not take you below the minimum stepdown altitude until the point where you're ALLOWED to descend below it, i.e., the charted glideslope-intercept point. So, once you're past the last stepdown, waiting for glideslope interception before beginning descent reduces workload instead of increasing it, with no degradation of safety that I can see.

As for how to do it on a checkride, I'll defer to CFIIs and DPEs on that.

 

Your eyesight is 20/20 on this one.

 

I've sent this to the FAA at 9-AJV-8-HQ-Correspondence@faa.gov which the AIM says is the place to make recommendations for changes.

Notice to Editor
The following comments/corrections are submitted concerning the information contained in:
Paragraph number 5-4-5 b. Instrument Approach Procedure (IAP) Charts, Note-2.
Pages 5-4-7 and 5-4-8 Dated 1/30/20
Pilot/Controller Glossary
Page PCG G-1

Dear Sir,
I have encountered much confusion and different 'interpretations' of Note-2. The first sentence, "The ILS glide slope is intended to be intercepted at the published glide slope intercept altitude" may tend to imply that a pilot may not intercept the Glidsope until this point. This point is labeled as the "FAF (precision approaches,)" in the Aeronautical Chart Users' Guide dated 21 May 20, page 109. Many documents refer to this as the PFAF, Precision Final Approach Fix. The Note does go on to explain that intercepting and tracking the glide slope prior to the 'Lightning Bolt,' which depicts the beginning of the Final Approach Segment is allowed, provided Stepdown Fix altitudes are complied with.

The Pilot/Controller Glossary defines Glideslope Intercept Altitude:
The published minimum altitude to intercept the
glideslope in the intermediate segment of an
instrument approach. Government charts use the
lightning bolt symbol to identify this intercept point.
This intersection is called the Precise Final Approach
fix (PFAF). ATC directs a higher altitude, the
resultant intercept becomes the PFAF.

It is a "minimum" altitude. The first sentence of Note-2 of AIM 5-4-5 b. seems to imply to many pilots that it as a 'hard' altitude and they must 'intercept' the Glideslope 'at' that altitude even though the requirement is to be at or above it at the PFAF. Perhaps that first Sentence should be removed and a less ambiguous explanation be given of the necessity to comply with Stepdown Fix altitudes outside of the PFAF. The term Precise Final Approach Fix shares an acronym, PFAF, with Precision Final Approach Fix. Precise Final Approach Fix is defined in the TERPS manual, Order 8260.3d, page B-9. It is a fixed point that is used in the construction of Non Precision as well as Precision Approaches. It is the point where Final Approach obstruction clearance criteria is applied. It does not move. The Glossary's explanation that the PFAF(precise) moves depending on where actual intercept of the Glideslope may take place by an individual aircraft is wrong.

Sincerely,

 

it is a distinct possibility, but only on a hot day, probably have to be around 85F or higher at the airport for ATC to see a deviation. On an ISA day the GS crosses GAATE at 5094 feet and HUNDA at 3693 feet.

 

I agree that it's less of a problem now than it was before they lowered the HUNDA altitude from 3,700 to 3,600 and moved both HUNDA and GAATE farther away from the runway. Here's what it used to look like before the changes:



As you can see, HUNDA was about 0.3 NM closer and had a min altitude 100' higher. GAATE was about 0.9 NM closer.

The changes helped, but it was (and still is) a big deal. So much so that the FAA has put out several Info notices specifically targeting the LAX approaches. So, my approved technique when I see something like this at work is to leave VNAV engaged until the FAP is the next fix, then capture the GS. That way there won't be any question about whether of not I'm going to make the crossing restrictions.

https://www.faa.gov/about/office_or...afs420/acfipg/media/closed/Hist 09-01-283.pdf

 

Yep. That would do it. And depending on the installation, arming approach mode will result in a smooth autopilot transition from VNV vertical path to GS/GP.

 

There may be a reason to stay at a higher altitude until intercept. For instance, if the charted intercept altitude is 3,000, but the cloud tops are 3,500 with icing conditions. I've done that before, and asked ATC to keep me up as long a possible. No reason to sit at 3,000 building ice waiting on the glideslope.