34 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 ...
  • 68.3k
9 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 ...
  • 4,571
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), ...
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 ...
  • 8,707
7 votes
Accepted

What is the reason for not providing glide slope guidance on the western approach to Innsbruck?

Looking at the charts, I can see quite a few good reasons for not providing glideslope for the West approach: The East approach leads you (almost) directly to the runway threshold, the West approach ...
  • 39.3k
7 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 ...
  • 70.7k
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 ...
5 votes
Accepted

Is a VHF NAV receiver inherently capable of processing a LOC signal?

Any VHF radio can receive the carrier signal of a LOC signal but to use it, you need dedicated circuitry. The LOC transmitter transmits the carrier wave, frequency modulated with two side lobes of ...
  • 30.9k
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 ...
  • 68.3k
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 ...
  • 1,189
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 ...
  • 18.2k
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 ...
  • 2,093
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 ...
  • 70.7k
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 ...
  • 43.3k
3 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 ...
  • 181
3 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 ...
  • 18.2k
3 votes

Can the ILS be shut down?

Yes. Usually, shutting down the ILS means shutting down the localizer and glideslope signals. There is more than one reason to 'shut down' the ILS. The ILS is designed to shut down automatically on ...
  • 99.1k
3 votes
Accepted

Can the ILS be shut down?

The ILS, or precisely the components localizer and glidepath antennas can be shut off, as they are electronic devices that emit radio signals. They can be turned off and on by ATC where required, e.g. ...
  • 15.6k
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 ...
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....
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 ...
  • 68.3k
2 votes

Why do some back course operations use normal sensing?

I-PKN localizer is not designed to "transmit backwards." In my opinion, it's actually the normal backcourse of the I-PKN localizer antenna that sits on a 11000 ft mountain. Its only purpose ...
  • 22.7k
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 ...
  • 5,629
2 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 ...
  • 7,796
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 ...
  • 27.1k
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 ...
  • 39.3k

Only top scored, non community-wiki answers of a minimum length are eligible