Why is the Inner Marker Beacon sometimes labeled "A" ?

[jwp_145]

I've noticed that in some aircraft, particularly older ones, the Inner Marker alerter is labeled with an "A". Outer marker is "O", Middle is "M", and sometimes the Inner is "I"(duh), but is often "A".

WHY?

[darrenf]

Originally Posted by jwp_145

I've noticed that in some aircraft, particularly older ones, the Inner Marker alerter is labeled with an "A". Outer marker is "O", Middle is "M", and sometimes the Inner is "I"(duh), but is often "A".

WHY?

I always thought of it as "Abort".

[flyer8]

From a website that is cached:

Now why is "A" used for the "Inner" marker you may ask? Here's the theory according to Tom. Years ago, there were things such as "Airway" markers that would go off when you flew over them. I've heard some are still in affect today but I couldn't find one. So the "A" is now used for "Inner" marker instead. Others say the "A" stands for " azimuth. But then, some of our more modern marker beacons, now say "I" and I know that's for inner! In any case, the white light means you are "very" close to the runway approach! Often the aircraft autopilot will look for an input from the outer marker to change the gain as well as some flight directors.

[Berkut]

Avionics manuals typically refer to them as an "airway/inner marker." I assume they used to use the same 3000Hz modulated 75MHz beacon for older airways.

[PeanuckleCRJ]

Interesting! With my music background, I always thought of it as "alto" which is a high pitch.

Go figure.

[taseal]

because back in the day, when you were on on an airway, the white one would light up and the a is for 'airway'

[VDEE7]

I think it stands for " An Inner Marker "