Middle Marker and Inner Marker

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John777

Pre-takeoff checklist
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I found out the statement on OM and IM in FAR that OM can be replaced with numerous means of navigation, also it states that IM is used for CAT II and III operation.

Now, when I looked at KMCO ILS approaches(CAT II, III), they had IM, and MM both, I was wondering because FAR does not specifically mention about MM.

Also looked at FAA Order on ILS and it says:

b. Marker Beacons. An Outer Marker (OM) or suitable substitute (refer to subparagraph 9c and Appendix A) is only required to indicate the final approach fix (FAF) for Nonprecision Approach (NPA) operations (i.e., localizer only). The FAF on CAT I/II/III ILS approach operations is the published glideslope intercept altitude, not the OM. Therefore, an OM or suitable substitute is not required for CAT I/II/III ILS approach operations. Middle Marker (MM) beacons are not required for CAT I/II/III ILS. An IM is only required for CAT II operations below RVR 1600 that do not have a published RA minimum (refer to Appendix A). CAT II operations with a published RA minimum do not require an IM.

Then why did KMCO airport establish MM for CAT I, II, III ILS approaches?

Thanks.
 
Maybe it was already there?

I do know that marker beacons are being phased out. Discovered that when I was installing my audio panel a couple years ago.
 
John777 said:
I found out the statement on OM and IM in FAR that OM can be replaced with numerous means of navigation, also it states that IM is used for CAT II and III operation.

Now, when I looked at KMCO ILS approaches(CAT II, III), they had IM, and MM both, I was wondering because FAR does not specifically mention about MM.

Also looked at FAA Order on ILS and it says:

b. Marker Beacons. An Outer Marker (OM) or suitable substitute (refer to subparagraph 9c and Appendix A) is only required to indicate the final approach fix (FAF) for Nonprecision Approach (NPA) operations (i.e., localizer only). The FAF on CAT I/II/III ILS approach operations is the published glideslope intercept altitude, not the OM. Therefore, an OM or suitable substitute is not required for CAT I/II/III ILS approach operations. Middle Marker (MM) beacons are not required for CAT I/II/III ILS. An IM is only required for CAT II operations below RVR 1600 that do not have a published RA minimum (refer to Appendix A). CAT II operations with a published RA minimum do not require an IM.

Then why did KMCO airport establish MM for CAT I, II, III ILS approaches?

Thanks.
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The MM has no purposes, and hasn't had for many years now. Why the MM still exists at KMCO is something only the FAA facilities folks know. The IM is for the CAT II approach only. It is at carefully surveyed location to coincide with the CAT II DA. But, even the IM is not required for CAT II if the special authorization permits use of certified radar altimeters. That 106 RA is also carefully surveyed. Further the IM serves no required purpose for either CAT I or III.
 
aterpster said:
The MM has no purposes, and hasn't had for many years now. Why the MM still exists at KMCO is something only the FAA facilities folks know. The IM is for the CAT II approach only. It is at carefully surveyed location to coincide with the CAT II DA. But, even the IM is not required for CAT II if the special authorization permits use of certified radar altimeters. That 106 RA is also carefully surveyed. Further the IM serves no required purpose for either CAT I or III.
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What was the purpose of the MM? My reading is that it is supposed to approximate the CAT I DA to remind you to go missed if you don't see the runway environment. What has changed that made the MM necessary before but unnecessary now? Better altimeters?

My guess on why KMCO still has a MM is that it's less work to keep than to decommission. Most things exist or don't exist in the world because of the relative work that someone would have to do to change them. But is it possible that some ground feature makes radar altimeters less reliable in that vicinity?
 
iamtheari said:
What was the purpose of the MM? My reading is that it is supposed to approximate the CAT I DA to remind you to go missed if you don't see the runway environment.
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That is correct. The MM should sound the dit dah about when you reach your DH. It is a nice and convenient reminder if you focus on the needles a lot and forget to watch the altimeter.

Radar altimeters are useful only on flat ground. Remember the Polish delegation that crashed in Russia? They relied heavily on the radar altimeter that was showing their altitude above the river, not their altitude below the cliff that the air base is situated on. :(
 
iamtheari said:
What was the purpose of the MM? My reading is that it is supposed to approximate the CAT I DA to remind you to go missed if you don't see the runway environment. What has changed that made the MM necessary before but unnecessary now? Better altimeters?
Click to expand...

For many years they were required. If your marker beacon equipment was inoperative you had to increase your DA (DH in those days) by 50 feet. Why did the FAA change this requirement? I guess for maintenance requirements and the fact that the area under the GS on a 200' DA ILS is quite a shallow surface that can't be impacted so long as the GS is not full fly-up.

My guess on why KMCO still has a MM is that it's less work to keep than to decommission. Most things exist or don't exist in the world because of the relative work that someone would have to do to change them. But is it possible that some ground feature makes radar altimeters less reliable in that vicinity?
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Beats me. They have removed a lot of them. More so with OMs there were some five miles from the airport and sometimes in bad neighborhoods.
 
BigBadLou said:
Radar altimeters are useful only on flat ground. Remember the Polish delegation that crashed in Russia? They relied heavily on the radar altimeter that was showing their altitude above the river, not their altitude below the cliff that the air base is situated on. :(
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Well, except for the radar decision altitude on most CAT II approaches. Those are very accurately surveyed. Also, two radar altimeters are required for CAT III fail-operational autoland. The RAs progressively take over from the ILS GS below 150 feet. Radar altimeters were also required to make the first generation GPWS work.
 
I miss middle markers. They were useful. Oh well. Nowadays I'm usually surprised to see anything flashing on my marker beacon receiver. Usually enroute over some old airport that still has one.
 
Back in the 80's, the MM at KMCO was a reminder to the locals to check the runway ahead for obstructions -- like an 8' alligator! Not in the FAR's but an alligator once in awhile wasn't unusual. I use to take my PPL students to KMCO during their night training to show the lighting systems on the 4 approach ends (this was before the Eastern runways were built). They all enjoyed landing on the BIG, WIDE, WELL LIT runway. Was always on the lookout for gators. But all this was way before KMCO became the big airport it is now.
 
Yep, back when I started my instrument training if you didn't have the MM you added 50' to the minimums or some fool thing. They removed that feature before I took the written.
 
I don't even gave a marker beacon receiver in my plane--I opted for an audio panel without one.
 
denverpilot said:
I miss middle markers. They were useful. Oh well. Nowadays I'm usually surprised to see anything flashing on my marker beacon receiver. Usually enroute over some old airport that still has one.
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Pop quiz: what was the purpose of the white light marker beacon before it was used for the CAT II Inner Marker?
 
The white light also flashes when you go over a fan marker. Not too many of them around. Rather than the string of dots that the inner marker plays, it does a dot-dash-dot sequence.
 
Also, the cone of silence over a L/F range station. The early range stations did not support ADF.
 
aterpster said:
Also, the cone of silence over a L/F range station. The early range stations did not support ADF.
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You've lost me. What does the cone of silence have to do with marker beacons? While they put fan markers on some A/N courses, they weren't directly at the station.
 
flyingron said:
You've lost me. What does the cone of silence have to do with marker beacons? While they put fan markers on some A/N courses, they weren't directly at the station.
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It wasn't a fan marker. Some pilots would miss the cone of silence so they installed a 75Mhz white marker at the site of the L/F range station transmission towers.
 
I had forgotten what it was called: The Z marker.

From a Barry Schiff AOPA article:

Most range stations also incorporated a Z marker that transmitted a steady 3,000-cycle tone and illuminated the white marker-beacon light as the aircraft passed over the station and through the cone of silence. Both the cone of silence and the reception area of the Z marker increased with altitude in the form of an inverted cone.
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If I recall correctly some airway markers were narrower when on course; those were called bone markers.
 
aterpster said:
I had forgotten what it was called: The Z marker.

From a Barry Schiff AOPA article:



If I recall correctly some airway markers were narrower when on course; those were called bone markers.
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Fan markers were (are?) designated by the "lens" shape as they are for the other markers. Indeed the bone markers look like dog bones on the chart.
 
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