Question about ILS/DME

[VW Pilot]

Got my 2007 FAR/AIM......

I decided to read a a bit through the front about ILS Aproach system.

SO..When you are shooting an ILS aproach and using the DME, when passing over the OM, MM and if category II ILS, IM.....the DME lights in the cockpit, do they just flash as you pass over each marker? or Does each light stay illuminated until you get to the next one?

I know nothing of Instrument flying....haven't even got my private yet. But I figured it would do me some good to start asking questions and reading ahead of time....Thanks.

 

[unreal]

The marker beacon lights flash only while flying over the marker. Also, you'll hear the morse code identifier for each beacon as you pass it (assuming you don't forget to turn that on ).

_ _ _ _ for OM
_ . _ . _ for MM
and . . . . for IM

 

[VW Pilot]

Done that a few times Eh??? heh heh heh....

Thanks.

 

[avbug]

VW,

DME means distance measuring equipment. It's a display that shows distance in nautical miles and tenths to a facility such as an ILS or VOR. The frequency is generally paired and automatically set when you dial in the facility frequency. In other words, dial the ILS frequency, and you receive both the ILS localizer, and the DME associated with it. Sometimes when flying the ILS, you need to dial a different frequeny for the DME...the DME for an approach may be predicated on another facility, such as a VOR, instead. The specifics will be spelled out on the approach.

The markers are AM radio stations that cover a very small area; they broadcast a continuous signal that will only be picked up when directly over the marker. This way, the marker annuncition in the cockpit (a light and a tone) serves to notify the pilot that he or she is directly over the marker.

Markers are gradually being decomissioned in favor of DME fixes and GPS fixes, to establish a precise position on an approach. On an ILS/DME approach, the use of marker beacons is redundant in showing one's position.

You'll often hear marker beacons referred to as compass locators, a NDB that can be used to home to or fly to or reference the marker beacon. For the purpose of the ILS, while on the ILS, they're the same thing except that a pilot using a RMI or ADF may be able to use the compass locator for reference and orientation at all times rather than just over the beacon itself.

Middle markers are being phased out for ILS approches throughout the US, and markers have been or are being phased out for many international approaches, too.

 

[minitour]

Markers are gradually being decomissioned in favor of DME fixes and GPS fixes, to establish a precise position on an approach. On an ILS/DME approach, the use of marker beacons is redundant in showing one's position.

Is there a cost benefit to the decomissioning of the MBs? Honestly, I can understand the MM...it doesn't really serve a purpose (IMHO) but the OM is always a nice reminder to the students that it's (/markerbeaconpitch "gear down gear down gear down") but if there's a substantial cost benefit, I guess I can understand it.

I realize that most (not all...maybe not even "most") people have GPS now and can readily identify any fix using the magic box, but for those that are flying /U, removing the Markers (unless there's a cross-radial) is going to be very limiting.

Curious,
-mini

 

[FL420]

Is there a cost benefit to the decommissioning of the MBs? Honestly, I can understand the MM...it doesn't really serve a purpose (IMHO) but the OM is always a nice reminder to the students that it's (/markerbeaconpitch "gear down gear down gear down") but if there's a substantial cost benefit, I guess I can understand it.

I realize that most (not all...maybe not even "most") people have GPS now and can readily identify any fix using the magic box, but for those that are flying /U, removing the Markers (unless there's a cross-radial) is going to be very limiting.

Curious,
-mini

All ground-based navaids require the purchase or lease of land, which is getting more and more expensive. They also must have scheduled and unscheduled maintenance and must be flight-checked by the FAA. The salaries, benefits and expenses of the large cadre of personnel to do this is quite expensive. It's no wonder the FAA is trying to get out from under that monthly nut in favor of space-based navigation aids.

The problem everyone is worried about is the reliability and security of GPS in the event of war, spoofing, terrorist attacks or large solar disruptions. This is why ground-based Loran C operated by the USCG is still around and being seriously considered as a back-up to GPS in the event of the unavailability of reliable GPS signals as other ground-based navaids are being decommissioned.

I would not be surprised to see navigation boxes start to appear on the market that combine GPS receivers with Loran C receivers if the decision is made to maintain the Loran C infrastructure as a GPS backup.

 

[VW Pilot]

Thanks Good info....Now what is backcourse? how and when is it used?
During missed approaches???

 

[AK47]

http://www.faa.gov/library/manuals/aviation/instrument_procedures_handbook/

 

[avbug]

I would not be surprised to see navigation boxes start to appear on the market that combine GPS receivers with Loran C receivers if the decision is made to maintain the Loran C infrastructure as a GPS backup.

They used to. I believe it was the KLN 89 or 90 used both LORAN and GPS, and selected the signal it liked best, FMS style.

 

[Princedietrich]

Thanks Good info....Now what is backcourse? how and when is it used?
During missed approaches???

The typical localizer transmitter that is associated with an ILS, or with a standalone LOC approach, transmits the signal in two directions. When you pass over the localizer array itself, which you typically shouldn't because it'll be installed at the far end of the runway, the signal doesn't just vanish completely. The signal will keep going and will continue to provide centerline guidance for that runway, in both directions.

Think of the localizer as transmitting two different signals, a blue signal and a yellow signal. As you come down the localizer course, you may receive blue more than you receive yellow. In this case the needle will point towards blue, which represents the left side of the localizer course and therefore the needle will deflect right (you're too far left, and have to correct right). The opposite will be true if you are receiving yellow more strongly than blue. If you receive both equally, the signal will be "green" so to speak and the needle will center.

A Localizer Back Course is a "cheapie" way to get a localizer approach to both ends of a runway with a single localizer transmitter installed. If there is an ILS or a LOC approach to runway 27, I can use that same transmitter and frequency for a LOC/BC approach to runway 9. I'm flying the same navaid to the same piece of conctete, but doing it in the opposite direction from what the navaid was installed for. Therefore, all of my indications will be backwards. If I am right of course, the needle will actually tell me that I'm LEFT of course. This is because of the way blue and yellow are broadcasting on their respective sides of the course. We call that "reverse sensing" and it can really sting you if you're not careful. Modern day indicators like an HSI or EFIS will eliminate the reverse sensing if used properly.

You can't just make up a LOC/BC course on your own, there has to be one published in the approach plates in order for you to do one. You can track a localizer's back course for your own purposes if you wish, they can make finding a runway a lot easier.

Clear as mud?