Anatomy of a low frequency aviation radio beacon

Discussion in 'Amateur Radio News' started by KX4O, Aug 25, 2020.

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  1. W7IMM

    W7IMM Ham Member QRZ Page

    There are a few of them left. I found one in Grandforks ND

    But since no one I know has even pulled up the volume control to listen to the MB receiver, I'm not sure how much safety is lost. I know it's been MANY years since I saw those lights light up.

    ......It's gonna be OK!! can let go now!!
  2. WX7LL

    WX7LL Premium Subscriber QRZ Page

    Middle and Outer Markers, where they still exist are largely used as a back-up for Cat III ILSs. They have been replaced by stand-alone DMEs at Localizers or GPS. Before I retired (2007) the FAA was maintaining them, but not taking extraordinary measures to keep them on the air. I had one OM next to a highway that we shut down because someone built a billboard right next to it, and a MM that was overrun by groundhogs that undermined the foundation and caused the antenna to tilt enough to alter the radiation pattern.
    KA0HCP and KX4O like this.
  3. KE4IKY

    KE4IKY Ham Member QRZ Page

    I don't see much of a purpose for them for Cat III ILS's and aircraft (or approaches). If I remember right (and I may not), the inner marker beeped and if you didn't see the ground by then, you had to go around. With Cat III aircraft, they can fly blind all the way down to touchdown (and on some versions of CAT III, the aircraft throttles have to chop power automatically). Cat IIIc (if I remember right again) of which there are none, allowed for taxiing after landing. Yes you can land a plane and not have enough visibility to taxi, I guess you just sit on the end of the runway and wait for the weather to clear.

  4. W7IMM

    W7IMM Ham Member QRZ Page

    You're right. The markers are pretty useless........... ALL aircraft that do CAT III approaches have Autothrottles during an Autoland approach and must be used. Autoland MUST be used unless a HUD is available, certified and the crew is trained. During a HUD CAT III approach and landing, the autopilot & autothottles must be disconnected and the aircraft is hand flown during the approach and landing.

    None of the approaches use OM or IM for anything since you're WAY past the IM when you get to DA

    If you can land out of a CAT IIIc, you can taxi as long as there's an approved low vis taxi chart AND you can see to taxi.....if you cannot see, you just stop and call for a tow.. Been there and done it more than once at SEATAC and Portland.
    When I retired we were good down to a 30' DA (Decision Altitude) on a Cat III approach.
  5. KE4IKY

    KE4IKY Ham Member QRZ Page

    AOPA says this, even the CAT IIIb can land "blind" and no one (at the time of the writing) (1997) had the Cat IIIc capability.

    In the Air force, generally the equipment was certified as CAT 1 but we always ran it to CAT 2 standards.


    "Cat IIIb autolandings — the lowest currently certified — may occur before any visual reference with the runway is established by the pilot. Since there is no "decision" to be made based on visibility, the approaches employ an alert height (AH) instead of a DH. The AH is merely a point above which a failure in certain required airborne or ground equipment mandates a missed approach. If the equipment failure occurs below the AH, the flare, touchdown, and rollout can still be safely accomplished by using redundant Cat III autoland components. Rather than using outside cues to ensure that landing is occurring in the touchdown zone, the crew may verify this by using onboard instrumentation and warning systems.
  6. W7IMM

    W7IMM Ham Member QRZ Page

  7. W7IMM

    W7IMM Ham Member QRZ Page

    Hmm....evidently I posted a quote of your last post and before I could finish the edit, the 30min time limit expired! Go figure!!

    Just flush all that AOPA 1997 stuff. It has all changed several times in the last 20+ years! Even the terms changed DH, AH, DA etc......

    The USAF only did Cat II approaches in the C-141 and C-17 The Autoland system although functional, was never used for Cat III (and never certified)

    At the company I retired from in 2018, we did ILS Cat III approaches to 30' DA. That's still current and the lowest visibility authorized now is 400ft (touchdown) 400 (Mid) and 300' (Rollout) RVR

    The fun part is that in certain cases, the Rollout RVR can be "inop" (or zero) in that case, you can land, rollout but you literally cannot taxi!

    AND, In that case, you land, roll to the end and call for a tug! ( I am SO GLAD I am retired!!!)
    Last edited: Sep 15, 2020
    KX4O likes this.
  8. KE4IKY

    KE4IKY Ham Member QRZ Page

    We're they ever able to use the MMLS (Mobile Microwave Landing System), or has that hit the wayside?
  9. W7IMM

    W7IMM Ham Member QRZ Page

    I seem remember reading about the "New" MLS in the 90's...... and I seem to remember the C-17 having the capability and or the equipment was to be installed "someday" but I never saw one in operation and we never trained with it. The mobile system obviously was supposed to be able to deploy anywhere affording a precision approach out "in the sticks".

    I am not sure aircrews would want to trust a mobile system that wasn't certified and well tested before attempting to use it!
  10. YOSUA

    YOSUA QRZ Member

    Very good article. My flight instructor never took me to visit a NDB transmitter. I only remember him showing me a VOR transmitter when flying just above it!
    KX4O likes this.

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