Navaid Theory

[RJP]

It's a long story why but...... I need to read up on & become completely familiar with the theory behind & useage of VORs, NDBs, ILSs, PARs, MLSs, GPS & DGPS, area & approach radar.

If I were in a proper country I'd go the nearest pilot supplies shop and probably pick up all of what I need. However, I'm in Bahrain, a speck of sand in the gulf where private aviation is banned, such shops are therefore non-existant.

So, can anyone recommend anything on the internet instead? Or, does anyone have the books detailing the above that I might be able to borrow?

Any info / help very much appreciated.

Rgds & thanks
Richard

[Tomliner]

Hi Richard.Have you had a look at www.msfsgateway.com ?Select the flight simulator navigation button which is under Tutorials..There may also be other links there as well.Don,t know whether this will be of any use to you.ATB EricT. PS Have a look also at http://www.aviation-links.co.uk

[emfrat]

Hi Richard -
You are sure to find something useful here:
http://www.auf.asn.au/navigation/index.html

There may be slight variations in local regulations around the world, but the basics are always the same.

MikeW

[RJP]

Eric / Mike,

Thanks for the info, that seems to take care of the useage part!!

Any ideas for something that'd cover the details of how the various aids function?

Cheers
Richard

[emfrat]

Richard -
The VOR section of the link I mentioned explains the basic electrickery needed to turn a Non Directional Beacon into a directional one. Once you are able to transmit 360 individual radials, you can limit the transmission to only a few of them, and there you have a Localiser. Lay it on its side and you have a Glideslope Indicator. Combine the two and you have an ILS.
The Microwave Landing System was developed to overcome the capacity limitations of the ILS. It uses much higher frequencies than VHF navaids, so it can process more data in the same timeframe.
A Global Positioning System receives directional information and time signals from a number of satellites. Its inbuilt computer uses triangulation calculations to establish the position of the receiver, in three dimensions. That means it can be used to hold an aircraft at a particular altitude, which the other two cannot.
All of these use instruments in the cockpit, which the pilot observes and responds to.
Precision Approach Radar is a refinement of the Ground Controlled Approach system. With both of these, a controller on the ground uses radar screens to locate the aircraft and he directs the pilot to the runway.
Some more links, with more technical stuff:
http://www.allstar.fiu.edu/aero/MLS.htm
http://www.centennialofflight.gov/essay ... Tech32.htm
http://www.casa.gov.au/pilots/download/ILS.pdf

Cheers
MikeW

[SkippyBing]

Its inbuilt computer uses triangulation calculations to establish the position of the receiver, in three dimensions. That means it can be used to hold an aircraft at a particular altitude, which the other two cannot.

Is that used much, as I understand it the vertical element is the least accurate in GPS for a range of reasons.

[emfrat]

A good point, Skip, and I should have phrased it better. To get an accurate position fix in 2D navigation, you want a good wide 'cut' between the sun line and the star lines. All the GPS satellites are in the same orbit, so it is difficult to get a good wide angle or three, to calculate altitude. The capability certainly exists, but I don't know if it is accurate/reliable enough to use on its own, within the rules of separation. Of course the alternative - a GSI with a horizontal beam for each FL- is perhaps not the most practical idea I have had
Cheers
MikeW

[SkippyBing]

Mike, I'm not 100% sure myself, I know SA when it was applied gave most error in the vertical. There's also the problem with the Earth not matching it's model perfectly for roundness. There is a satellite being launched to detect variations in the Earth's gravity that's going to use GPS for accurate position fixes in all three axis but I'm guessing they're not viewing the Earth as a fixed frame of reference. As most of my flying tends to be below 3000' it's never really been an issue!

[Chris Trott]

In the US, the only way to get a full precision approach with GPS including vertical navigation is when WAAS (Wide Area Augmentation System) gives the required correction to the GPS constellation to refine both the lateral and vertical position errors to within 6 inches. Without it, the variation is 30 feet laterally and 100 feet vertically, leading to why a non-WAAS GPS approach is more accurate, but not allowed to lower minima than a VOR approach. All non-WAAS GPS approaches simply create a virtual glideslope based off of the position information for the end of the runway and a given displacement to the "touchdown point" and displays that. It uses the aircraft's inbuilt precision altimeter to determine based on distance from that calculated touchdown point as to whether it's on the "glidepath" or not, disregarding the GPS altitude.

As an aside, the WAAS system is available to ALL users and transmits a non-directional signal, thus many handheld and vehicle-based GPS systems that have been produced in the last 5 years are equipped to utilize this signal when available to give a similar refinement in location.

[Nigel H-J]

Hi Chris May be wrong but believe that WAAS is only available in the US at the moment, any ideas in how long will it be before it is extended?

Regards
Nigel.