reply to post by nh_ee
Yes...that's why I jumped when you wrote "LORAN". Wrong implications. LORAN (very, very outdated for aviation use, today....but of course, used back
then) is for LO
avigation, using low frequency (90 - 110 kHz) transmitters and airborne receiving equipment. Generally,
it was suitable for those long over-water routes. Low frequencies propagate further, and aren't subject to line-of-site restrictions. I am old
enough to have used a version of it (way back) and I forget what we called it! Old age, I suppose.....but, it was essentially the same thing, and of
course, this was well before GPS became so commonplace. We had only two or three 727s with the equipment installed...out in the Pacific.
ADF (NDB) ....usually interchanged, and it confuses people. N
eacon is the facility that is doing the
transmitting, on the ground. It uses the AM radio band spectrum, actually...just below it to be exact. A
inding (or "finder") refers to the instrument onboard that receives the signal from the NDB, and how it's interpreted by the pilot.
All it is, is a needle that POINTS in the (usually vague and general) direction of the transmitter. Subject to interference, and static...and signal
bounce. It's rather inaccurate, and thus hardly used for Instrument Approaches anymore....though, we DID have to learn back int he day, AND do them
in the Simulator. Many, many times, just in case we ever had ONLY that to rely on in real world, some day.
The ADF instrument has a compass bezel that can be rotated, for pilot's orientation and situational awareness when navigating via the NDB signal.
A modern ADF instrument, typical for light airplanes:
The knob lower left corner rotates the compass rose bezel.
Modern airliners still have the ADFs (so far)...and those have compass roses that are synced to the other compass systems, and "turn" to always
reflect current airplane heading.
In those cases, and what I am familiar with, they are called an "RDMI"....Radio Directional (or, "Distance")Magnetic Indicator...or somesuch. Like
(The orange, and orange/white striped "flags" indicate power is off to the instrument --- makes sense, since it's not installed!!! OR, they indicate
an improper signal of some sort, or other fault).
The orange "HDG" flag refers to the compass rose fault....in this case, no power.
Those two rectangular buttons, you push them, and they cycle each needle (the thin single, or the wide double) to point towards either a tuned NDB, or
VOR, depending on pilot's choice.
The indicator near the button will change, as shown....if you could push the one on the left (if this were interactive) then it would next read "---->
VOR". Push it again, and it's back to "----> ADF"...etc.
This instrument also incorporates the DME windows, to display that feature. DME is associated with TACAN (the military version of VORs) and MOST (in
the USA) VORs are actually "VOR/TACs"....A VOR and TACAN station co-located.
(TACANs operate in the UHF frequency spectrum, VORs in the VHF spectrum. DME receivers can receive, in UHF, only the distance info...azimuth signals
aren't available for civilian airliners, from the TACAN).
edit on 25-9-2010 by weedwhacker because: Image size