"unmonitored" navaids

[BeechBoy]

First of all, what precisely does this term mean? I have never seen a formal definition. My understanding is that all NAVAIDs are electronically monitored but, what, exactly, is being monitored? Will someone know only if it goes out of service completely or will they also know if erroneous data is being transmitted?

I just finished watching the video in which a 767 almost crashed because the ILS it was following was transmitting erroneous glideslope data (the ILS was NOTAM'd as "unmonitored"). This has caused me to wonder what precautions should be taken in the event an "unmonitored" NAVAID is being used for an approach.

Does the fact that you're receiving the identifier GUARANTEE that the NAVAID is working PROPERLY? Does the identifier AUTOMATICALLY go off the air if the NAVAID fails a self test or does a human have to manualy take the identifier off the air in the event of a failure? (In other words could a NAVAID that is unmonitored go out of commission and still be transmitting its identifier?) Long ago I heard Richard L. Collins make the statement that as long as he's trusting his life to a NAVAID that he's going to constantly monitor the identifier. I have adopted this philosophy and, even though I SHOULD get warning flags if something is amiss, whenever I'm shooting an ILS I always have the identifier playing softly. I'm just wondering what additional assurance this provides.

I know the glideslope altitude can also be verified by checking it at the marker but (I hate to admit this) I often forget this in the heat of battle.

[meritflyer]

All it implies is the electronic link bewteen the NAVAID and the controlling agency is down so they cannot monitor and ensure the integrity of the nav signals provided.

The identifier is usually removed only when mx is being performed on the VOR.