glideslope unmonitored? DME sound ?

[newmei]

What is exactly does it mean when you get a notam saying localizer, glidesloop unmonitored? Is this important to us? What exactly does it mean? (reference please also!) Also why exactly do some audio panels have a audio selection for the DME? How can you hear DME? This is new to me? Is it for those that you seperatly entered the navaid feq then identify that box so that you have the correct navaid in the self contained dme radio?

 

[MattM]

DME emitts a tone at 30 second intervals. Thats why you would listen using the audio panel. There are some instances where a VOR is out of service, but the DME is not. Also my guess on the localizer, glide slope unmonitored means exactly that. They are not monitored by the FAA for their accuracy. I am sure someone can fill us in on this.

Matt

 

[siucavflight]

All glideslopes and localizers are checked for accuracy by the FAA. If they were not then they would not be legal to use for navigation (Nor would you want to.) Sorry NEWMEI, i do not have any sources but my guess is that this equipment is at an uncontrolled field and while being at that field you are not able to be seen by anyones radar.
Good question though, again this is just my best guess, i am going to have to go and dig out the old bible to get an answer.

 

[abexpilot]

I recently attended a CRM class where we watched a video detailing a near accident involving a 767 operated by a New Zealand air carrier. Long story short, the flight was to an airport with an unmonitored glideslope. The autopilot captured a false g/s signal and began a descent which would have put the aircraft into the ground well prior to the runway. The crew did a great job of recognizing the error by referencing other navaids as well as their "gut feelings" and were able to execute a go-around before the aircraft was in any danger. During the video, an in depth explanation of how a g/s and localizer operates was given as well as what "unmonitored" means. According to the video, the g/s and loc antennas have a sensor placed just in front of them that "monitors" the signals that are generated. This sensor is connected to an alarm (as well as back up transmitters) located in the tower. In the event of a problem with the signals the alarm is triggered and the tower can alert the air crews. In the New Zealand case, the line leading from the sensor to the tower was disrupted due to construction at the airport, hence the g/s and loc signals were unmonitored. Also in this case, I think the backup g/s transmitter was out of service. I would highly recommend this video to all flight crews and their training departments. Hope this helps.

 

[great cornholio]

The DME does emit an ID every 30 seconds and it is a higher tone than the VOR. So if you are trying to ID a VOR and only hear a tone once ever 30 sec then the VOR part should be considered unusable but the DME should be accurate. I have seen some audio panels that have the DME switch and all it does is just give you the DME ID and NOT the VOR so if you hit that switch that way you should hear the ID once every 30 sec. Also remember that the VOR and DME are two totally seperate navaids they just are paired up on the same freq, but besides that operate sepereately hence the 2 seperate IDs. As far as what LOC G/S unmonitored means my best guess is that the status of the LOC G/S cannot be confirmed by ATC. Most places have a some sort of box that has red and green lights (at least the ones Ive actually seen in person) that show the status of each element green means that part is working fine red means there is some sort of problem. At controlled fields this box is usually in the tower and at uncontrolled fields the box is usually at the airport managers office or the fbo or somewhere that someone can see it pretty often. So if it is unmonitored and the G/S is out then ATC can't advise you beforehand that the G/S is out. But if they have the box and they look and see that the G/S light is red then they can be like cessna 1234 cleared for the ILS runway 1 glide slope out of service. Well thats my best guess, hope it helps.

 

[siucavflight]

thank you for the information, it really helped

 

[xjcaptain]

Also, it's not a bad idea when you ID the nav's (you do ID NAV's right!?) to listen to both. Can prevent some embarassment/confusion if it is forgotton that the DME is being held from another NAV sorce. Just make sure both morse codes match, just different tones.

 

[cvsfly]

Learned something new. Maybe I'll be more careful selecting an alternate. From Doc's FAR Forum:

I hope this helps!

Regards,

Doc


FAA Order 8260.19C, Ch 8, Sec 3, para 812(b)(1) and (2):
b. Alternate Minimums.
(1) To qualify for alternate minimums, an airport must have weather reporting at the airport and the weather must be reported on Service A weather sequences. Commercial operators who have an approved weather reporting service may be authorized alternate minimums without the requirement for Service A hourly aviation reports.

(2) Chapter 2 of this order defines facility monitoring categories (1, 2, 3, and 4) and utilization of these categories. Alternate minimums shall not be denied on precision SIAP's if the OM or authorized substitute does not have a remote status indicator. This is because the ILS/MLS is monitored, and the GS/GP provides intercept and descent guidance. However, this does not apply to nonprecision SIAPs or the LOC/AZ portion of an ILS/MLS SIAP; i.e., deny alternate minimums on a nonprecision SIAP if the facility is not monitored. Alternate minimums are NOT authorized on LORAN-C SIAPs.

 

[Anaconda]

one other reason...in the army (can't speak for other services) whether the apch navaids were monitored or not affected the weather minimums/requirements you needed to file/fly IFR (don't ask me how, i've been out too long)...

 

[throttlejockey]

I read about and saw the same video as abexpilot is talking about. abexpilot and great cornholio are right on about unmonitored glideslopes.

In the Air New Zealand scenario, the glideslope was unmonitored, so the tower did not know that after maintenance personnel were finished checking the calibration of the g/s, the maintenance people failed to switch the g/s system from "mx" back to "normal". Therefore, the g/s was sending out a calibration signal instead of a normal signal - thus the aircraft on approach was recieveing and tracking a signal that indicated that they were dead-on the g/s the entire time! The astute crew onboard new something was not right but did not execute a missed approach until they were very close to the ground.

The moral of the story is as follows:

- Always tune and identify your navaids.

- Always check your notams.

- When flying ANY ILS approach, make sure you brief your crossing heights so that you know what altitude you should see at each point across the approach.

- If you are using DME, make sure you have the proper DME set up in the radios.

You need to know how far you are from the runway at all times so that a bad G/s signal does not guide you into the ground.

tj