Abc Vor U/s
 

hey boys n' gals,

Did it ever happened to you that you saw on the NOTAMs that the "ABC VOR is U/S" (un serviceable), but while flying to the ABC VOR it was working perfectly?

If it happened to you too, and it sure did to many here, you were probably wondering for what reason is that NOTAM up in the air.

As far as I know when it says "ABC VOR unmonitored" it means that it might be working but it's not legal to count on it as a navaid (specially in IMC), since it's not being monitored for integrity and/or operational status.
But I always thought the "ABC VOR U/S" meant that it's not working.

So what does it mean if not that it's just simply not working?

Possible reasons

a) The monitoring has indicated a problem. Not sure why they would leave it one but I have seen that. Maybe on the premise that some guidance is better than no guidance to VFR folks who didn't get the NOTAM?

b) Routine calibration or troubleshooting is in progress...they need it on to adjust it.

c) The problem is fixed but they have CANX the NOTAM yet.

Did you listen to the ident?

ABC unmonitored means that it is not possible to use that navaid for the purpuse of an alternate. This is why the alternate requirements for a lot of part time towers will say "N/A as alt when XYZ tower is closed" because the tower monitors the navaid locally.

Unmonitored also means you should not use it as the principle navaid for IFR period.

I'm curious as to where the FAA says that?

I don't know that they do, but it's common sense. It might not be an option if an ILS is unmonitored due to the tower being closed. In that case I would be satisfied with some secondary system to cross-check the ILS (GPS, LOM, VOR cross-fix, etc). I think most, but not all, ILS's are monitored by the TRACON who will clear you for the approach.

Monitoring is just another layer of aviation redundancy...the more of those you take away the shorter you lifespan is going to get.

For instance, I know of a few approaches that I have accomplished that, when the tower is close, is unmonitored. I would assume that by saying that the FAA is saying, it could fail, but we won't know unless you tell us.

For what I have gathered talking FSS and ATC guys is that Unmonitored simply means that there is no FAA facility making sure that the station is still putting out an accurate signal. When a VOR is unmonitored, the FAA has no real-time idea whether it is working or not but they assume it is still working until a pilot tells them otherwise. Once notified, they will mark it as OTS and send a crew to check it out.

Legally, I have found no FAR, AIM, IPH, IFH, PHAK, or any 135 Ops Spec (company specific) references to any legal significance behind using an unmonitored navaid for navigation under IFR.

Specifically...
-14 CFR 91.181 - IFR Course to be flown says, "On an ATS Route.." or "on the direct course between navigational aids..." with no mention to unmon navaids.
-14 CFR 91.169 - IFR Flight Plan Requirements (alt req's) says mentions the 1-2-3 rule with no mention to unmon navaids either.

As far as I can tell, there is no legal function behind an unmonitored navaid. It seems to be just an advisory for pilots. If anyone has any FAA references that explain unmonitored navaids in more detail, please share!

The only other thing I have found concerning navaids and their use as primary nav under IFR is this excerpt from AIM Chapter 1...

AIM 1-1-19 (e) - "Use of GPS for IFR Oceanic, Domestic En Route, and Terminal Area Operations"
(2) "GPS domestic en route and terminal IFR operations can be conducted as soon as proper avionics systems are installed, provided all general requirements are met. The avionics necessary to receive all of the ground-based facilities appropriate for the route to the destination airport and any required alternate airport must be installed and operational. Ground-based facilities necessary for these routes must also be operational.

This could call into question exactly how an unmonitored navaid relates to an operational NAVAID. The way I figure is that since the FAA tells us about non-operational navaids by means of the "OTS" NOTAM notation, I tend to think that unmon DOES NOT constitute a navaid NOT being operational simply because if the FAA wanted to tell a pilot that a navaid was Out of Service, then they would NOTAM it "ABC VOR OTS" not "ABC VOR UNMOM!" Although this sounds good to me, I do concede that there is a certain level of ambiguity between Operational and Unmonitored simply because the FAA doesn't tell us anywhere EXACTLY what unmonitored means.