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39 votes
Accepted

How is varying modulation depth achieved by localizer ground transmitters?

The beam strength decreases as you move away from it's own centreline, so is it actually that the entire modulated signal strength decreases which when de-modulated is effectively a difference in ...
mins's user avatar
  • 74.5k
10 votes
Accepted

If DME is required, why have non-DME minima?

Conceivably the I-ETI DME transponder could be out of service, preventing you from identifying YOCUB (unless you have a second VOR or GPS), but you could still identify BASSO on the CHS DME for the ...
pericynthion's user avatar
  • 4,640
8 votes
Accepted

Telluride (KTEX): Why is the localizer antenna located where the glideslope should be?

The localizer for runway 09 is offset by 3°, almost certainly because of terrain. That would be a typical reason for a non-standard installation. The approach plate for the LOC RWY 09 approach notes ...
Pondlife's user avatar
  • 71.8k
8 votes

Can I execute an ILS approach using a NAV CDI with LOC signal only?

No, you cannot execute an ILS approach without an ILS glide slope indication as the primary form of vertical guidance. Even if you could supplement it with alternatives (WAAS, GPS software, etc), ...
Ryan Mortensen's user avatar
8 votes
Accepted

What prevents the use of a multi-segment ILS for non-straight approaches?

See here, pages 5-23, 5-24. Things have advanced well beyond ILS for that kind of approach. https://whispertrack.com/pdf/faa_handbook.pdf REQUIRED NAVIGATION PERFORMANCE The operational ...
CrossRoads's user avatar
  • 8,795
7 votes

Why can a localiser be used without a glideslope, but not vice versa?

Because there would be no benefit to doing so. where the pilot uses the glideslope for vertical guidance but relies on ground- or satellite-based navigation fixes for lateral guidance. As you ...
60levelchange's user avatar
4 votes
Accepted

What's exact offset degree dividing localizer and LDA?

The maximum angular offset for a LOC is 3° for FAA and 5° for ICAO. Everything else is named either LDA (FAA) or IGS (ICAO). In ICAO wording, any ILS which doesn't meet all ILS requirements is an ...
mins's user avatar
  • 74.5k
4 votes
Accepted

What is the reason to have LOC/VNAV landing method?

A VNAV with localiser approach is normally a backup to a regular ILS should there be a glide slope unserviceability. The use of VNAV to manage the vertical portion of the approach would allow the use ...
vectorVictor's user avatar
  • 1,229
4 votes

Why do some back course operations use normal sensing?

This procedure is unusual mainly because it uses a remotely installed localizer for a missed procedure. A backcourse used in a localizer approach is not unusual, the uniqueness here is that that the ...
2NinerRomeo's user avatar
  • 2,223
4 votes

How to fly LOC approach when IAF is a specific DME from LOC, but LOC has no DME?

You have a few different points here but the short version is: IWA is a VORTAC and I-IWA is a localizer, i.e. they're different navaids. DME is available from IWA and it's optional but not required ...
Pondlife's user avatar
  • 71.8k
4 votes

What are the procedures for flight checking a glideslope and localizer?

It's all laid out in Order 8200.1D United States Standard Flight Inspection Manual. That and other documentation, including the inspection reports can be found from the FAA website under Flight ...
Gerry's user avatar
  • 19.9k
4 votes

Why do localizer/glideslopes use 90/150Hz specifically?

An AC motor in the USA will turn at 60 RPM and 90 is 3/2 and 150 is 5/2 of 60. Both can be generated using a simple gear drive which would reduce the costs during development. Similarly there are ...
Javelin's user avatar
  • 201
4 votes

Why do localizer/glideslopes use 90/150Hz specifically?

The frequencies are chosen to allow the system to produce a localizer and glideslope 'beam' that provides proportional guidance that can adequately guide an aircraft on the approach. Read through ...
Gerry's user avatar
  • 19.9k
3 votes

How to interpret/use "Fix Minimums" (at KALB)

Short answer, if you can identify WESTS, then you cross it at or above 820 and then go on down to your MDA of 620. If you can't identify WESTS then your MDA is 820. Since the approach requires radar ...
Ralph J's user avatar
  • 51.8k
3 votes

When do I execute a missed approach on a LOC approach when I can't identify the MAP?

Well, I’m not an FAA guy so I can’t find the relevant FAR quote, but going more general: ICAO Doc 8161 Vol 1 - Aircraft Operations I-4-6-1 6.1.4 Note 2 In the case of a missed approach with a ...
Radu094's user avatar
  • 7,970
3 votes

Why do some back course operations use normal sensing?

The key issue here seems to me how to set up the instruments and what the indications will be. For an HSI you set the CDI to the front course, i.e. in this case to 303 and you will get correct sensing....
Ken Karas's user avatar
3 votes

Why are the modulation depths of the localiser and glideslope different?

From the book "Principles of Avionics" By Albert Helfrick: The amount of modulation is twice that found in the localizer. Because the glide slope does not have ident or speech audio, the ...
Fiddlesticks's user avatar
  • 3,781
3 votes

How to calculate the vertical profile for a LOC only approach?

I built a calculator to help with these types of calculations. https://my.rockymountainflight.com/canpa You can input the icao identifier for an airport. I pull up the current METAR for you. You input ...
Tom Nunamaker's user avatar
3 votes

Can a Localizer Backcourse signal be reversed (at the site antenna)?

Can we reverse the guidance from the transmitter? Can a Localizer Backcourse signal be reversed (at the site antenna)? From a technical standpoint it's entirely possible, but both beams, front and ...
mins's user avatar
  • 74.5k
3 votes

"w/o DME" minimums on DME required approach

DME is required equipment for the approach procedure, but note that the LOC DME minimums only apply to the Localizer DME functioning. The missed approach holding pattern references the VORTAC DME, ...
Romeo_4808N's user avatar
  • 73.9k
2 votes

How the Log Periodic Dipole Antenna of Localiser help in varying modulation depth?

Mod Depth (more commonly called modulation index in electrical engineering) is the amount a carrier signal is modulated. Mod depth has nothing to do with antenna configuration and is set by the ...
DLH's user avatar
  • 5,809
2 votes

Why are the modulation depths of the localiser and glideslope different?

In short In addition of the two navigation tones 90 and 150 Hz, the LLZ signal can contain two other components: a telegraphic identification tone of 1020 Hz, a voice channel, between 1 kHz and 3 kHz ...
mins's user avatar
  • 74.5k
2 votes

Why do localizer/glideslopes use 90/150Hz specifically?

When ILS was developed, they actually used rotating capacitive plates with lobes. The 90 had 3 lobes and the 150 had 5. Easy way to modulate the RF with the phases locked. The depth of modulation was ...
Charles Bader's user avatar
2 votes

What prevents the use of a multi-segment ILS for non-straight approaches?

Even if it were technically possible to have a multisegment ILS approach, the economics just don't make sense. Each ILS costs millions to install and millions more to keep running properly over its ...
StephenS's user avatar
  • 27.7k
2 votes

Why can a localiser be used without a glideslope, but not vice versa?

Let's consider the ILS on its own, with no supplement navigation aids like RNAV / GPS. Assume IFR conditions. A LOC+GS approach can get you onto the runway. A LOC-only approach simply won't work, you ...
kevin's user avatar
  • 39.7k

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