Can you be a little more specific about what this might be? I sometimes get an IAN when I think that I am set up for an ILS. What might I be doing wrong?
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You need to make sure you have both ILS frequencies set on the nav radios and both inbound courses set up on the MCP. Unlike the 787, the FMC on the 737 has no influence on how you fly an ILS, other than it draws a pink string on the map. In the 737 it’s spit and sawdust and just like it is in a light aircraft. Tune the frequency, set the course and fly it.
The reason you’re getting IAN indications is because, I’m guessing, you haven’t set the actual ILS up correctly. In lieu of an ILS signal the auto flight system is doing what it’s supposed to and falling back to the next level of approach, in this case an IAN approach based on what’s loaded into the FMC.
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Well I did check at the time to see if I had the ILS freq set properly in the radios so I am pretty sure that the ils was set. I will try it again. Perhaps that ILS is inop for some reason.
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Easy to forget setting the ILS inbound course on both the pilot and copilot side, as both need to be set as posted above. This can be done enroute, during cruise when workload is light, before descent (can also be done on the ground before departure on very short flights in many cases). Good flying!
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In EASA there’s a limitation called the MUH (Minimum use height). I think the FAA does not have it. That’s the minimum height at which the autopilot can remain engaged engaged during single channel operations (No autoland). In my airline on the 737-800 the MUH is 158ft (140ft AAL on the 737-700). This means the single A/P needs to be disengaged at 158ft or higher.
Additionally we have a rule not to practice hand-fly when above FL200 so technically you could fly manually all the way from FL200 to touchdown (Sometimes I do when reasonable and outside of busy airspace).
On a normal day where you don’t feel like handflying the approach and whenever it’s not reasonable to increase the workload by not using automation I’d say we normally disconnect the autopilot after the landing checklist is completed and the airplane is in final configuration at around 2-3nm from touchdown. Sometimes a bit earlier.
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Thank you very much for your detailed explanation! I’m writing all this stuff down.
At the moment underway to Copenhagen (Kastrup) I’ll practice it straight away.
-Bram
IAN is not a part of the large majority of 737s; it is an option that only some operators use. These tend to be the operators who are trying the hardest to shortcut training profiles; IAN (if you only need to fly the simplest of RNAV procedures) allows the elimination of one or two approach profiles to train.
However, it does not allow for curving or offset approach procedures, the minimums are typically higher (and never lower) than an RNP .10 procedure to same runway… And the autopilot can remain engaged to approach minima (or lower) on any type of approach flown, in my world. I understand it may be different elsewhere.
For perspective, I fly for the 737 operator that invented RNP (AR) procedures 20-something years ago, so we are quite entrenched in that world. I can see how it might be different for an operator that rarely flies RNAV procedures.
Point is, if it’s included in the PMDG, it should be a configurable option, not something that’s just always on… Since the majority of 737s don’t have it installed in the first place.
Practically speaking, unless it’s important to have one less approach profile to train, there is no practical benefit to using IAN. It never gets you lower, it doesn’t reduce workload (there’s nothing simpler than LNAV/VNAV all the way down), and it drastically limits the types of RNAV procedures that can be flown.
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In MSFS, different ILSs seem to have different ranges. If you arm approach mode before you’re receiving good loc/gs indications, you’ll inadvertently arm IAN. Watch for FAC / GP flight guidance modes, instead of LOC / GS.
I wouldn’t say it’s all about training shortcuts. IANs can be helpful. Example: a radio-based non-precision approach, instead of diving-and-driving for each stepdown. IANs provide a more stable approach and reduces crew coordination there. That’s especially true when you’re at the end of a 24-hour crew duty day, at a location none of the crew has been to before, you’re trying to listen to challenging ATC accents, a non-precision is the only option, and there’s some poor weather. Seeing something that looks like an ILS is much nicer than rolling the vert speed down to your stepdown fixes and MDA. I’ll train to the challenging stuff, but prefer to simplify things when able.
That’s not what IAN does. IAN doesn’t provide extra approach capability - it changes the presentation and way the crew interface with the FMC final approach course. The database construction is identical. IAN simply allows the crew to project the final approach course back infinitely to create a pseudo FMC localiser and glidelsope. As mentioned earlier, if crews are trained to fly these approaches in LNAV/VNAV it is actually simpler than IAN. VNAV will build the correct deceleration into the final approach and then will pick up the glide path angle - all whilst staying in VNAV PTH. No IAN trickery or VS required. Also I assume you’re referring to military ops by your username, but there’s no such thing as a 24hr duty day in the airline world.
You can fly a straight-in VOR or LOC approach using step-downs and vert speed, and multiple altitude changes, or you can use IAN and get an ILS like approach. That’s what I’m trying to highlight.
Yep, airlines don’t have 24 hour duty days, but I do! And I’d prefer to use an IAN at the end of one of those days if my option were that or multiple step-down fixes. IANs aren’t as useless as it sounds like people are making them out.
IAN is hardly difficult to train. It’s a case of asking is the final approach course a straight line from the FAF to the runway? It is, great, fly it in exactly the same way you would fly an ILS. Job done. I think I maybe did one as a look-see on the conversion course and that was it. A small classroom brief and maybe 5-10 minutes max in the sim itself.
Many 737’s don’t have the option because they pre-date its introduction. It’s standard on all 787, and the guys I know still fly the 737 day it’s standard on all their new aircraft, even in the lowest of low cost airlines.
We’re clearly going to have to agree to disagree, but IAN is literally the dictionary definition of ‘simpler than LNAV/VNAV all the way down’. It’s literally the point of it. It also allows you to keep the autopilot and flight directors engaged below minima (on the 787 at least), something other non-precision approaches don’t allow for.
ps As long as an approach meets the criteria above (straight line) then it can be flown as an IAN. As I’m sure you know they’re not specific IAN approaches, IAN is just an easier way to fly an existing RNAV profile between the final fix and the runway. It would be a strange airline that doesn’t teach its crews to fly a more traditional LNAV/VNAV approach in lieu of an IAN. Why would you do that?! Let me know who does and I’ll avoid ever flying with them.
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Looks like there’s some regional differences at play. In my part of the world we fly RNP approaches in LNAV/VNAV PTH. We can also leave the automation engaged down to 50’ RA. Although not the best idea as they are still a baro-derived approach. IAN does nothing other than move the INTC CRS functionality from the CDU to the MCP and show the deviation on the PFD using LOC/GS presentation rather than NPS scales. The actual approach you’re flying is identical either way. I assume you guys are being vectored onto these approaches? In that case yeah it would make it a little neater.
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We would fly that in LNAV / VNAV, and there would be zero stepdowns. You could be cleared for the approach 30 miles out and as long as you’re on a transition or cleared direct a fix, and have verified constraints in the FMC, it’s LNAV / VNAV path, dial field elevation in the MCP, and fly a continuous glidepath all the way to minimums. No setting multiple restrictions and certainly no vertical speed.
It is a rare approach that needs flown in vertical speed; it typically involves an intermediate stepdown that penetrates glidepath. In that case, IAN doesn’t work either.
I didn’t mean IAN was difficult to train, I meant that it allows airlines to save on training LNAV / VNAV RNP approaches. Low cost airlines tend to like this.
My airline operates the youngest fleet in the US and one of the youngest in the world. We’ve never had a use for IAN, because LNAV / VNAV IS simpler, and more capable. If you fly for an airline that operates Boeings, you should have access to the same Boeing sales data I do and you can see what a small percentage of 737s are equipped with it for yourself.
We don’t fly the 737 (more’s the pity!) anymore but even if we did I doubt I’d have access to sales data as a line pilot to be honest.
I’m genuinely interested by how you see LNAV/VNAV as simpler and more capable. IAN is only to be used inside the FAF and standardises the procedures & SOPs with an ILS, it’s not an either/or. Often I use LNAV/VNAV to fly me inside the FAF then engage approach mode and with it FAC & G/P. As I said, at the end of a long flight, in the dark and perhaps on a rainy, crosswind sort of night, being able to keep the automatics and flight directors in is often invaluable in preserving capacity and allowing us guidance to touchdown. IAN gives us that whilst LNAV/VNAV doesn’t. The two complement each other rather than competing in my opinion.
On a more general point, if low cost carriers are trying to save money by not training their crews how to fly the full suite of RNAV approaches available to them I can’t help but feel their penny pinching has gone a bit too far. Not a criticism, just an observation.
@Rowdus What aircraft type is letting you leave the autopilot in to 50’ RA on a non-precision approach?
Perhaps regional differences are at play here? As far as sales data / equip options, that is disseminated via our fleet captain’s office. We don’t see who gets what of course, but numbers of aircraft produced with various options. IAN simply isn’t commonly included. My personal anecdote to support that is that I commuted for 15 years (thankfully that ended 10 years ago), meaning I’ve spent far too much time in the jumpseat of almost every airline in the US, and I don’t know of one that has IAN in 737s. That doesn’t meant there ARE none, but if I’ve never encountered it it’s certainly not what you’d consider widespread.
I think LNAV/VNAV is simpler precisely because it doesn’t require any mode changes and takes you right to the runway. Does is not, for you? I honestly don’t know how other regions might handle that… For us, you can remain coupled down to DA / DDA / MDA on any non-precision approach, and then even after the autoflight is disengaged you’ve still got flight guidance to touchdown.
All that being the case, I don’t see any advantage to IAN. But if there are regional differences at play then it might explain why it’s rare in the US but might be more common elsewhere?
I’ve also never heard of anyone going coupled to 50 feet on a non precision approach; 73s can do that on a cat I ILS, but not a non precision. Here, anyway.
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How would you know if they have IAN fitted unless you’ve asked them? 
Surely the MCP is standardised.
It’s all fair discussion because we’re slightly comparing apples and oranges. Almost all my 7.5K hours on the 737 were on the 3, 4 & 500 which ran on coal. On the 787 IAN is standard and was integrated into the design from day 1.
IMHO, the big win with IAN is that it it standardises the procedures for RNAV, GPS, VOR, NDB, LOC, LOC-BC, LDA, SDF & TACAN (amongst others) approaches. It gives you the ability to capture from above just like an ILS whereas an LNAV/VNAV approach doesn’t give you that. In an ideal world that would never be needed but ATC somehow always conspire to make life harder than it needs to be. In highly dynamic or non-normal situations there is less chance of a mistake being made which I would suggest is the whole point of the feature in the first place.
I’m sure on short haul when you’re maybe doing 2 landings and 4 approaches in a day (at the correct time on your body clock) that’s not perhaps as big a concern, but on long haul you can often be bumping along recency requirements and flying difficult approaches into unfamiliar airfields in what is the middle of night as far as you’re concerned after 13 hours flying. Anything that reduces the chances of a mistake at that point is a good thing.
Of course, none of that answers whether or not the IAN should or should not feature on the PMDG 737 
Well now there’s another difference: we can certainly capture a VNAV Path approach from above; I couldn’t tell you how many times I’ve done it. Why wouldn’t it work for you? What would happen? We regard it as safer than capturing an ILS from above.
Your laundry list of approaches is why I think LNAV / VNAV is easier ; we’d fly them all in LNAV / VNAV ( minus an actual ILS). Effectively, we’ve got 1 approach profile for all non-precision approaches (there are very rare cases where vertical speed may be necessary but functionally it’s only something you see in the sim once a year.). And our one non-precision approach profile works on ALL non-precision approaches, from an NDB to a .10 RNP (AR) with multiple RF segments. IAN can’t do that. And the LNAV / VNAV profile requires no mode switching.
Believe me, I can appreciate fatigue. Our route structure is such that I can be in JFK on day one, Anchorage on day 2, Hawaii on day 3 etc, with plenty of WOCL flying in the mix. But we probably do almost as many RNAV approaches as we do ILSs, so I don’t see one as easier or more familiar - thus lower threat to fly in a fatigued state - than the other. I guess if you fly very few RNAVs to begin with, something that masquerades as an ILS might be more familiar?
We had -400s and NGs when I started. The -400 was a pretty capable airplane; it was what was used to develop RNP (AR) procedures for the first time and was a good Southeast Alaska airplane. It didn’t skip off ground effect like a supercritical airfoil will; when you pulled the power it just landed. Was a lot nicer to crank through the cut into Juneau than a Max 9 is, for sure haha.
I’ve got friends at all major US airlines of course; you don’t spend 25 years in the industry without knowing a few people. We’ve discussed RNAV stuff at length, in addition to me watching many non-precision approaches as a commuter in the jumpseat; I’m familiar with how they fly. I do not know of anyone using IAN in 73s here. But maybe someone can chime in if they know of some.
As far as the PMDG, I think IAN is a great option to include - as long as it is as option, since the majority of 73s don’t have it. A higher percentage have HUDs, and THAT’S an option in the PMDG.
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re The PMDG aircraft, why does it need to be an option? If you don’t wish to fly one, don’t fly one. Just push two less buttons. Am I missing something obvious there?
Yeah, of course we can capture a VNAV profile from above but the procedure to do so is different from an ILS, as per the FCTM. The whole point of the IAN is to keep the procedures uniform across all types of approach, as far as the IAN lets you. The FCTM specifically says not to use the ILS/IAN capture from above technique for a VNAV approach because if you screwed it up it’s a CFIT waiting to happen. We can only ever capture a VNAV profile from above in VNAV, whereas an ILS/IAN we would use vert speed. On a normal day no big deal, but should circumstances conspire against the wrong crew on the wrong day then there is merit in more standardised procedures.
Equally, on another point, the 787 FCTM specifically says not to arm approach mode until the aircraft is established on the localiser, yet as noted further up many airlines allow this. That has always been the rule since the day I started flying and it’s amazing how many ways airlines find to skin the same cat!
ps I didn’t particularly like the -400. I much preferred the -300, even though it was smaller it was much more stable. The -400 was incredibly speed unstable in gusty conditions.
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