FAR AIM Inner vs Middle Marker

[455 Bravo Uniform]

What am I getting wrong here? If the MM is on the glide path about 200 ft above the touchdown zone, then how can the IM which is further along the glide path be at the decision height, me presuming that ILS DH is also usually 200 ft. What am I reading or understanding incorrectly? Section 1-1-9 (f) (2) b & c:

 

[Greg Bockelman]

My semi wild a** educated guess is that it would be the DH for a Cat II approach which is approximately 100 feet in most cases.

 

[dmspilot]

Notice it says "a decision height" not "the decision height". IM's are only installed for >= Cat II approaches which have decision heights of less than 200 feet.

 

[champ driver]

But what's the frequency for the MM on an ILS?
I got that question on a test once, as if it would make any difference what it is.

 

[dtuuri]

But what's the frequency for the MM on an ILS?
I got that question on a test once, as if it would make any difference what it is.

I'd like to offer my take on this since it goes to the heart of a lot of the complaining about written tests.

"If it doesn't matter in the real world, why ask a question about it, like which way to turn a certain knob, etc.," goes the complaint. Well, I don't think written tests are trying (or were trying) to establish that the taker knows the minimum knowledge needed, at least not by direct questioning. I think the FAA simply is (or was) looking for evidence the test taker studied the reference books. Consequently, I don't think the written scores are evidence of knowledge extent. Memorizing answers to cherry-picked questions can result in a perfect score, but look at all the reference material missed! On the other hand, somebody scoring 70% who actually studied all the material, but couldn't remember a few tidbits of knowledge like all marker beacons broadcast on 75 mHz, is far better prepared for flight.

 

[Tarheelpilot]

If the ils has cat 2 mins it may have a IM. If there is terrain around and the plate says radar altimeter NA then the IM is used for DH

 

[bobmrg]

All marker beacons transmit on 75MHz; it is fixed and you cannot tune it, just turn it on or off (depending on your switch panel)...we're not talking low-frequency locator beacons here.

Bob Gardner

 

[luvflyin]

If the ils has cat 2 mins it will have a IM. If there is terrain around and the plate says radar altimeter NA then the IM is used for DH

LAX has lots of CAT II Approaches without IM’s

 

[bflynn]

You descend to the decision height, then fly at that height until you reach the MAP and determine if you can see the airport. The MM could be at the decision altitude, which just means that the FAA expects you to reach the decision altitude at the MM, not the IM.

I think.

 

[luvflyin]

You descend to the decision height, then fly at that height until you reach the MAP and determine if you can see the airport. The MM could be at the decision altitude, which just means that the FAA expects you to reach the decision altitude at the MM, not the IM.

I think.

NO!!! That’s what you do with an MDA. At DA you miss NOW!

 

[bflynn]

precision vs non-precision.

Non precision, you fly at the MDA to the MAP, which is the situation I was trying to describe. Precision, you go missed at the DA/DH. Imprecise language from a student.

Of course, reading the picture, again, it does say ILS, so I'm not sure what they're trying to say.

 

[flyingron]

All marker beacons transmit on 75MHz; it is fixed and you cannot tune it,

The carrier frequency is indeed 75Hz in all cases. It's modulated with various tones (400Hz for the outer, 1300Hz for the middle, 3000 for the inner). This is how your marker receiver distinguishes it and causes the lights to light up. In addition, for the blind and tone deaf, the sequence of the tone beeps varies (long pulses for the outer, alternating short long for the middle, short for the inner).

Fan markers are so obsolete these days that the FAA has deleted them from the AIM, but there are still a half dozen around. They use the same 75MHz and use a short-long-short beep of the same frequency as the inner (so your I light will light up).

I have no idea what a "low frequency" marker is. Fan markers were often placed on LF airways, but they were not "low frequency" themselves.

 

[bflynn]

Ok - the MM would put you 200' higher than the TZE, but 200' isn't necessarily the DH. Higher category systems can have much lower decision heights.

Better?

 

[dmspilot]

You descend to the decision height, then fly at that height until you reach the MAP and determine if you can see the airport. The MM could be at the decision altitude, which just means that the FAA expects you to reach the decision altitude at the MM, not the IM.

I think.

Just delete your post because you're not even close. The question has been answered correctly so why would you post this BS?

 

[bflynn]

Because I'm student trying to understand? Of course, I'm more confused now because apparently I know nothing. Thanks for clarifying

The question I heard from the OP is why does the AIM say that a MM will be at 200' above the touch down elevation, but then there is also an inner marker definition. Maybe it was subtle, but I didn't hear the answer.

If I am wrong, then tell me what is right. Or just say that it's wrong and I'll try to figure it out on my own. Don't be a jerk about it.

 

[Tarheelpilot]

LAX has lots of CAT II Approaches without IM’s

Do you see any IM on cat I only approach es?

I’m not familiar with LAX. I don’t fly internationally

 

[455 Bravo Uniform]

Yes, like @bflynn I’m trying to learn instrument stuff. The AIM didn’t make sense, but I doubted it was because it was written wrong or a mistake, but rather because I don’t know jack yet.

So my answer is probably: MM may be at 200 ft, which is the same as the lowest DH in Cat I ILS, and the IM may be lower for other Cat (II, III) systems. (EDIT - “Systems” is wrong, should have said “Procedures”, right?).

So IF my understanding is correct, here is my next question- if I hear the MM, and I’m on glideslope, and the airport enviro is NOT in sight, that MM is just one additional situational awareness tool that I’m at minimums and need to go missed?

Let’s be clear here- I have zero instrument ground time, and zero in the plane (other than for my PPL). I’m learning the hard way by reading (same as I did for my PPL, before actually starting instruction). So I have no CFI yet...

 

[dmspilot]

Yes, like @bflynn I’m trying to learn instrument stuff. The AIM didn’t make sense, but I doubted it was because it was written wrong or a mistake, but rather because I don’t know jack yet.

So my answer is probably: MM may be at 200 ft, which is the same as the lowest DH in Cat I ILS, and the IM may be lower for other Cat (II, III) systems.

So IF my understanding is correct, here is my next question- if I hear the MM, and I’m on glideslope, and the airport enviro is NOT in sight, that MM is just one additional situational awareness tool that I’m at minimums and need to go missed?

Let’s be clear here- I have zero instrument ground time, and zero in the plane (other than for my PPL). I’m learning the hard way by reading (same as I did for my PPL, before actually starting instruction). So I have no CFI yet...

On an ILS the marker beacons are situational awareness tools only...with a couple exceptions such as Tarheel pointed out where terrain would make a radar altimeter unusable on a Cat II or greater approach. Otherwise arrival at decision altitude/height is the missed approach point.

On a localizer-only, the outer marker or fix used in lieu of the outer marker is usually the final approach fix and the MAP is usually determined by time or DME.

 

[aterpster]

LAX has lots of CAT II Approaches without IM’s

The IM is a relic of the early days of CAT II when not everyone had a radar altimeter (RA). There are still IM's where the terrain at the DA point won't support an accurate RA height.

 

[aterpster]

On an ILS the marker beacons are situational awareness tools only...with a couple exceptions such as Tarheel pointed out where terrain would make a radar altimeter unusable on a Cat II or greater approach. Otherwise arrival at decision altitude/height is the missed approach point.

Not, "or greater." Radar altitudes are surveyed only for CAT II.

 

[aterpster]

Because I'm student trying to understand? Of course, I'm more confused now because apparently I know nothing. Thanks for clarifying

The question I heard from the OP is why does the AIM say that a MM will be at 200' above the touch down elevation, but then there is also an inner marker definition. Maybe it was subtle, but I didn't hear the answer.

That training material is very old. MMs stopped being part of an ILS perhaps 20 years ago. Way back when, you had to add 50 feet to the Decision Height if the MM was out of service or your marker beacon receiver was inop.

 

[luvflyin]

Do you see any IM on cat I only approach es?

I’m not familiar with LAX. I don’t fly internationally

I don’t see any Marker Beacons anywhere at LAX

 

[bobmrg]

"I have no idea what a "low frequency" marker is. Fan markers were often placed on LF airways, but they were not "low frequency" themselves."

Ron. by asking the frequency the OP gave me the impression that he thought it was tunable, like a locator beacon. Did I say "low frequency marker"?

Bob

 

[flyingron]

Yes, I was just explaining that it was the modulating tone rather than the frequency that differentiated the inner from the middle.

 

[Tarheelpilot]

I don’t see any Marker Beacons anywhere at LAX

Ok. What’s that have to do with anything

So I re read my original post and changed will to May.

All precision approaches don’t have markers but some do. They are there for situational awareness and in some cases for approaches below cat I mins are used for the decision height.

 

[PilotRPI]

Yes, like @bflynn I’m trying to learn instrument stuff. The AIM didn’t make sense, but I doubted it was because it was written wrong or a mistake, but rather because I don’t know jack yet.

So my answer is probably: MM may be at 200 ft, which is the same as the lowest DH in Cat I ILS, and the IM may be lower for other Cat (II, III) systems. (EDIT - “Systems” is wrong, should have said “Procedures”, right?).

So IF my understanding is correct, here is my next question- if I hear the MM, and I’m on glideslope, and the airport enviro is NOT in sight, that MM is just one additional situational awareness tool that I’m at minimums and need to go missed?

Let’s be clear here- I have zero instrument ground time, and zero in the plane (other than for my PPL). I’m learning the hard way by reading (same as I did for my PPL, before actually starting instruction). So I have no CFI yet...

Good luck! Enjoy the journey. I just got my rating last week and used the same method. A few FAA pubs, the FAR/AIM, and lots of questions to my instructor. At first it seemed totally overwhelming, but after figuring a few things out, it all starts to come together in a very cool way.

 

[davidgfern]

Because I'm student trying to understand? Of course, I'm more confused now because apparently I know nothing. Thanks for clarifying

The question I heard from the OP is why does the AIM say that a MM will be at 200' above the touch down elevation, but then there is also an inner marker definition. Maybe it was subtle, but I didn't hear the answer.

If I am wrong, then tell me what is right. Or just say that it's wrong and I'll try to figure it out on my own. Don't be a jerk about it.

The DH for an ILS approach depends upon the Category of the ILS approach being flown. The most common ILS approaches are Category 1, and these have a decision height (usually) of 200 AGL..... that is where the MM is located. However, certain ILS approaches can be flown to lower minima than that ..... if the pilot and aircrew have specific training and the aircraft is properly equipped, etc. A Category 2 ILS has a DH (usually) of 100 AGL . These approaches have an IM placed where the glide slope is 100 feet above the ground. If you are flying a Category 1 ILS, the IM is not used as part of the approach procedure. Hopefully this clears things up for you.

 

[davidgfern]

Yes, like @bflynn I’m trying to learn instrument stuff. The AIM didn’t make sense, but I doubted it was because it was written wrong or a mistake, but rather because I don’t know jack yet.

So my answer is probably: MM may be at 200 ft, which is the same as the lowest DH in Cat I ILS, and the IM may be lower for other Cat (II, III) systems. (EDIT - “Systems” is wrong, should have said “Procedures”, right?).

So IF my understanding is correct, here is my next question- if I hear the MM, and I’m on glideslope, and the airport enviro is NOT in sight, that MM is just one additional situational awareness tool that I’m at minimums and need to go missed?

Let’s be clear here- I have zero instrument ground time, and zero in the plane (other than for my PPL). I’m learning the hard way by reading (same as I did for my PPL, before actually starting instruction). So I have no CFI yet...

The MM is usually, (but not always) placed at the point where , if you are on the glide slope, you are 200 AGL, however the MAP is defined by whatever the DH/DA on the approach plate says.... as I said, for a Category 1 ILS this is USUALLY where the MM is located, but it is not ALWAYS true.

 

[aterpster]

Yes, I was just explaining that it was the modulating tone rather than the frequency that differentiated the inner from the middle.

More importantly, the light. MM: Orange, IM: White. Of course, which light is activated depends upon that modulating tone, which I don't believed anyone listened to except for the old airway makers (bone and fan).

 

[aterpster]

The MM is usually, (but not always) placed at the point where , if you are on the glide slope, you are 200 AGL, however the MAP is defined by whatever the DH/DA on the approach plate says.... as I said, for a Category 1 ILS this is USUALLY where the MM is located, but it is not ALWAYS true.

Are they any MMs still in existence?

 

[flyingron]

Are they any MMs still in existence?

We still have one near here (Mid-Carolina RUQ). But boy at the big airports they seem to have been replaced by and large with DME fixes. It's pretty amazing. When I started on my instrument rating, there was still a 50 foot penalty on the ILS for not having the MM.

 

[aterpster]

We still have one near here (Mid-Carolina RUQ). But boy at the big airports they seem to have been replaced by and large with DME fixes. It's pretty amazing. When I started on my instrument rating, there was still a 50 foot penalty on the ILS for not having the MM.

I see an OM there, but not a MM.

 

[flyingron]

I see an OM there, but not a MM.

One of each on the NACO plate. I've not been over there recently to see if it's still operational. That place, by the way, has the ugliest localizer antenna array I've ever seen.

 

[aterpster]

One of each on the NACO plate. I've not been over there recently to see if it's still operational. That place, by the way, has the ugliest localizer antenna array I've ever seen.

Interesting. Only the OM on the Jepp chart.

 

[flyingron]

Yep, apparently a NACO charting error (I'll report it). It went OTS two years ago:

RUQ 02/006 RUQ NAV ILS RWY 20 MM OUT OF SERVICE 1702241239-PERM

 

[flyingron]

Just got an email from the FAA:

Thank you for your inquiry regarding the middle marker on ILS OR LOC RWY 20, Salisbury, NC (RUQ).
We will be correcting the chart to remove all reference to the middle marker for the 4/25/19 effective date.
We appreciate your making us aware of this!

 

[Artimas]

I can't remember the last time I shot an approach with marker beacons.

 

[Jeff Oslick]

I can't remember the last time I shot an approach with marker beacons.

I think it was in 2008 for me.

 

[flyingron]

I can't remember the last time I shot an approach with marker beacons.

Nor could I. I only remembered the one at RUQ (now gone) because I used to fly over it and hear it beeping on departure.

 

[mtuomi]

Are they any MMs still in existence?

KATL has multiple. 26L, 27R.