Marker Beacons - Who Needs Them?

Updated: Feb 21

Update 2/20/2020

AIM Section 1-1-9 Instrument Landing System has been updated in this version, which is not yet in my 2020 printed copy.

- "ILS systems may have an associated OM. An MM is no longer required."

- "4. The following means may be used to substitute for the OM: (a) Compass locator; or (b) Precision Approach Radar (PAR); or (c) Airport Surveillance Radar (ASR); or (d) Distance Measuring Equipment (DME), Very High Frequency Omni−directional Range (VOR), or Nondirectional beacon fixes authorized in the Standard Instrument Approach Procedure; or (e) A suitable RNAV system with Global Positioning System (GPS), capable of fix identification on a Standard Instrument Approach Procedure."

- "Due to advances in both ground navigation equipment and airborne avionics, as well as the numerous means that may be used as a substitute for a marker beacon, the current requirements for the use of marker beacons are: (a) An OM or suitable substitute identifies the Final Approach Fix (FAF) for nonprecision approach (NPA) operations (for example, localizer only); and (b) The MM indicates a position approximately 3,500 feet from the landing threshold. This is also the position where an aircraft on the glide path will be at an altitude of approximately 200 feet above the elevation of the touchdown zone. An MM is no longer operationally required. There are some MMs still in use, but there are no MMs being installed at new ILS sites by the FAA;"

I think that pretty much closes this topic. Very few reasons remain to install or maintain marker beacon receivers and it can be taught as a history lesson along with NDB/ADF to instrument candidates.

Kudos to the FAA for following through on the feedback given.

Update 3/7/2019

A further update from the FAA with specific answers to my questions - see below. Based on this, I would say that marker beacon equipment is not worth any maintenance investment, that marker beacon setup should not be on a standard check list. In theory, there may be a localizer approach (not: ILS, but it could be an ILS with glideslope out) out there that would require an outer marker to identify the FAF with no alternatives, but I haven't found one. It may be worth a 10 minute discussion in the IFR curriculum, but that's pretty much it. Note that an ILS can be flown without an OM in all cases, as the FAF is defined by glideslope intercept.

From the FAA:


If there is a MM, do I need to use it? Answer:

No, reference to MM was removed from §91.175 (k) in 2007. (See link to Area Navigation (RNAV) and Miscellaneous Amendments above. Since then middle markers have been gradually phased out with over 95 percent of them being decommissioned to date. The remaining middle markers are charted if they are operating but there is no requirement to use MM.


Why did I need it in the first place? Answer:

You didn’t (since 2007).


If they have it, should I teach my future students to set up marker beacons as part of their setup check list? I believe, based on the above, the answer should be No – but again, not clear.


This question would be better directed to the Airman Testing Branch. I cannot provide a yes or no answer to that question but here are some variables to consider:

· FAA-S-ACS-8B, Instrument Rating ‒ Airplane Airman Certification Standards June 2018 Preflight Procedures objective is “to determine the applicant exhibits satisfactory knowledge, risk management, and skills associated with managing instruments appropriate for an IFR flight. The applicant must demonstrate a knowledge of VOR, DME, ILS, marker beacon receiver/indicators.”

· The AFM/POH for the airplane being flown may specify how avionics preflight checks are to be performed.


Do I need to invest in (the repair of) a marker beacon receiver? The answer appears to be No – placard it as inop indefinitely.


That is an owner decision. If you absolutely must fly a certain localizer approach with an outer marker and the only way to identify the outer marker is by using the airplane’s marker beacon receiver and suitable ground or airborne substitutes are not available the answer would be yes. If the airplane avionics certification and/or AFM/POH does not require a marker beacon and you can find an option other than the aforementioned localizer approach the answer could be no.

Related to the suitable substitute discussion:

As a CFII you will want to be familiar with ongoing approach chart changes related to required equipment and how it is annotated on the approach chart. A link to an Aircraft Owners and Pilots Association (AOPA) article on the subject is provided.


Update on 1/31/2019: the FAA responded to my feedback as follows:

Mr. Adriani,

We are in receipt of your request to define in the AIM; fix identification can be substituted with GPS or DME on Final in place of Marker Beacons used on a conventional ILS System.

Our office is currently coordinating with the appropriate stakeholders who need to weigh in, to obtain concurrence with your proposal. ......

I earned my instrument rating in 2001 and am working to add my second I (Instrument) to my CFI certificate and am trying to catch up on things. One of the things that have me stunned by the lack of clarity is the fate of the Marker Beacons.

Marker Beacons used to be an integral part of the Instrument Landing System (ILS), and according to the AIM, they still are. The Marker Beacon, in theory, provides a well aimed bundle of signal at specific points during the final approach - specifically: the Outer Marker (OM) gives an audible and light signal at glide slope intercept; The Middle Marker (MM) provides and audible and visible signal at (or around) Decision Height. The Inner Marker (IM) does something for Cat II approaches, which is not all that relevant for most of us.

I haven't used marker beacons for my instrument flights (mostly: instrument currency flights) for a long time, and doing a bit of research, I find out that there's a good reason: all marker beacons in our area have been decommissioned.

Marker Beacons were (are, supposedly, according to the AIM) often co-located with low power Non Directional Beacons (NDBs) called Compass Locators. These were handy a long time ago, as they gave a bit more situational awareness when maneuvering for an approach in the era before moving map GPS displays. But of course, like the Marker Beacons, NDBs have mostly been phased out.

So this raises a bunch of questions, including:

- If an ILS still has marker beacons, am I supposed to use them?

- Do my approach minimums change if I don't use marker beacons?

- What has taken over the role of the marker beacons?

- Should the setup of marker beacons be part of my approach check list?

- Do I need a marker beacon receiver?

I am not finding authoritative references that directly answer all of these questions - which is interesting. There's a web of archaic information that sometimes completely ignores the existence of GPS. Even the AOPA has a current article that kind-of broaches the subject, but based on data published by the FAA in 1998 and since clarified at least once. So, here goes:

If an ILS still has marker beacons, am I supposed to use them?

- AIM 1-1-9-a-4 tells me that " Precision radar, or compass locators located at the Outer Marker (OM) or Middle Marker (MM), may be substituted for marker beacons. DME, when specified in the procedure, may be substituted for the OM. "

- AIM 1-2-3-a-1 says that a 'Suitable RNAV System' (which is defined before it, but an IFR GPS with current database should suffice), can be used to ' Determine aircraft position relative to, or distance from a VOR (see NOTE 6 below), TACAN, NDB, compass locator, DME fix; or a named fix defined by a VOR radial, TACAN course, NDB bearing, or compass locator bearing intersecting a VOR or localizer course. '

So let me get this straight: if I have a OM without a compass locator (known as Locator Outer Marker or LOM), I can use a DME in lieu of the OM, and I can use the GPS in lieu of the DME. So far so good. But if there is a MM without a compass locator, I still don't know if I'm allowed to do this.

- Do my approach minimums change if I don't use marker beacons?

Well, the 'INOP Components' table in the approach plates no longer have any indication that approach minimus change if the marker beacons are out of service. But if it is in service and you don't have the equipment (or not turned on) - still don't know.

- What has taken over the role of marker beacons?

Looks like in real life, DME and GPS have taken over the role of marker beacons. The role was 'Range Information'. The Outer Marker can explicitly be replaced with DME - and implicitly with GPS (see above), but the function of Middle Marker perhaps should have been questioned, as barometric altitude (the Decision Height, as listed on the minimums) should really mark the missed approach point on an ILS, not a marker or a DME/GPS reading.

- Should the setup of marker beacons be part of my approach check list?

This is where I am starting to transition to opinion, as I can't find a good reference at the moment (but I will update when I do). So don't base your defense on this. But I believe that in the current system, the NAV/COM setup should include four main steps:

1. VOR/Localizer frequencies/ID

2. GPS or DME setup (and ID)

3. OBS setup

4. COM setup

I don't think marker beacons should be on this list anymore. This is complicated enough, and marker beacons don't appear to add enough value.

- Do I need a marker beacon receiver?

Again: opinion... I don't think I would install this anymore if it is optional. If it doesn't function in my airplane, I would placard it indefinitely and not spend money to repair it. It seems like marker beacons are like NDBs, and having a receiver for them doesn't appear useful.

Please reach out to me with any better ideas or references. In the meantime, I am going to use FAA's offer to provide feedback to maybe update the AIM chapter to provide better guidance for today's IFR system.


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