C203 Week 3 - Aviation - Obsidian Publish

# ATAC203 Avionics Systems > # [[C203 Week 2| ◀️ ]]  [[C203 Home| Home ]]  [[C203 Week 4| ▶️ ]]               [[QR C203T SSGW03| 🌐 ]] [📝](https://excalidraw.com/) > # [[C203 Week 3#ATAC203 Avionics Systems|Week 3]] >- [[C203 Week 3#VHF Omni-Range Navigation VOR|VOR]] >- [[C203 Week 3#Instrument Landing System ILS|ILS]] ^65aa7c >[!jbPlus|c-blue]- Lesson Intro >### What > >We now have learned some of the technology behind avionics systems. We will now move on to looking at how these systems work. > >### Why > >These systems are key to the operation of aircraft that you will work on. > >### Testing > >You will be tested on this material on the Midterm and on the Final Test. > >### Approach and Objectives > >By understanding the following topics, you will have achieved the learning outcome for this lesson. Consult your course outline for the learning outcomes and other details of this course. > >#### Course Learning Objectives >- CLO 7. Explain principles of VOR >- CLO 8. Explain principles of ILS >‼️ We now proceed to learn about 17 systems. You may find [this method](https://excalidraw.com/#json=DbVuRsjvs1aIS_8tp77Qv,HWbNqPeNoyUVJgtZWJxyKw) helpful to make sure you have an organized view of the material. ## VHF Omni-Range [[faculty/student/references/glossary/Navigation|Navigation]] (VOR) >[!aside]- Ref [[VOR|🗺️]] ### VOR Purpose and Description %%==[[Faculty/Student/Content/C203/Master QB#Q00100|Q]]==%% - Enroute, station to station [[faculty/student/references/glossary/Navigation|navigation]] system - [[Heading]] and [[Bearing]] Information - Positional Fix (paired with [[DME]]) [[VOR]] is an enroute, station to station radio navigation system. It provides heading and bearing information, and is used to create airways in the sky. It assists in providing positional fixes, and for this purpose is frequency paired with a DME station. This means that for a given VOR frequency, there is often an associated or paired DME frequency. We will learn more about DME a little later. In 2000, there were 3,000 VOR stations worldwide. This number is decreasing as more and more stations are being decommissioned and being replaced by Global Positioning System ([[GPS]]). GPS has the advantage of increased navigational accuracy, as 2 VOR beacons at 2 Nautical Miles offers a 90m accuracy, while GPS is closer to 10m. In Canada, more VOR stations are going defunct, and eventually this system will cease to operate. However, never forget that you may be working on legacy equipment for quite some time still. VOR still works, and is quite effective, and is still in wide use in many areas of the world. ### VOR Components - Ground %%==[[Faculty/Student/Content/C203/Master QB#Q00107|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00124|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00215|Q]]==%% [[Pasted image 20201228205712.png|➡]]![[Pasted image 20201228205712.png|350]] Ground components include a VOR station, with a central [[antenna]], as well as a circular array of antennas. This circular array is a distinctive physical feature of VOR stations. [[Pasted image 20201228210056.png|➡]]![[Pasted image 20201228210056.png|350]] VOR stations are often co-located with [[DME]] transponders, as well as [[TACAN]] (Tactical Air Navigation, a military system). Symbols on pilots' charts will indicate this as follows: [[Pasted image 20201228210145.png|➡]]![[Pasted image 20201228210145.png|350]] ### VOR Components - Onboard Onboard components of the VOR include the following: #### Control Head [[Pasted image 20201228210234.png|➡]]![[Pasted image 20201228210234.png|350]] #### VOR Receiver %%==[[Faculty/Student/Content/C203/Master QB#Q00095|Q]]==%% [[Pasted image 20201228210323.png|➡]]![[Pasted image 20201228210323.png|350]] As we will see with other systems, in larger aircraft, you can expect to locate the receiver in an [[avionics bay]], with controls and displays in the cockpit. [[Pasted image 20201228210417.png|➡]]![[Pasted image 20201228210417.png|350]] Smaller aircraft often employ a panel mounted receiver, with controls for the pilot to select the VOR frequency. #### VOR Antenna You will see some variation in VOR antenna design, but they often have two blades or protrusions. [[Pasted image 20201228210502.png|➡]]![[Pasted image 20201228210502.png|350]] [[Pasted image 20201228210508.png|➡]]![[Pasted image 20201228210508.png|350]] [[Pasted image 20201228210513.png|➡]]![[Pasted image 20201228210513.png|350]] #### Interconnecting wiring and antenna coaxial cable Also part of the system is the required wiring for power, interconnection, and signal to and from the antenna. This component of the system is often responsible for some of the trickiest snags. But because this component is there for every system, it will not be mentioned again. ### VOR Theory of Operation #### Station Radials The ground VOR station projects straight line radials from the station in all directions. These radials are radio waves that emanate out from the VOR ground station from the circular array and the central antenna. The radials projected from the station are referenced to magnetic north and extend outward from the VOR station. Because of this reference to magnetic north, VOR bearings correspond to magnetic bearings. We learned last week that magnetic north moves over time. How does this affect the VOR? It means that over time, it's reading will be off by the [[declination]] accumulated since its manufacture. It is aligned with [[Magnetic North]] as it leaves the factory, and is not normally adjusted afterward. We will look at radials a bit more, and then we will see that pilots effectively fly these radials, making the fact that the numbers are off a little less important. Radials are identified by numbers from 0° to 359°, and correspond to the degrees of a [[faculty/student/references/glossary/Compass Rose|compass rose]]. Don't forget that 0° refers to [[magnetic north]], and not [[true north]] or [[compass north]]. [[Pasted image 20201228210744.png|➡]]![[Pasted image 20201228210744.png|350]] Aircraft in flight can determine their position by detecting which radial they are on, and so their position can be described in relation to the station. When an aircraft is flying from a VOR station, it is said to be flying on a radial of that VOR station. However, when an aircraft is flying to a VOR station, is is said to be on a bearing to the VOR station. The use of these two terms may seem confusing, but as you will see, we do have to distinguish whether an aircraft is flying to or away from a VOR station, and this terminology helps to keep this straight. [[Pasted image 20201228211424.png|➡]]![[Pasted image 20201228211424.png|350]] %%- [ ] #JB redo this graphic 🛫 2023-01-17%% In this graphic, in the first case you see an aircraft on a due east course, that is 090°, flying over a VOR station. Approaching the station, it is on the 270° radial but leaving the station, it is on the 090° radial. So, to keep it straight, approaching, the aircraft's bearing to the VOR station is 090° (even if it's on the 270° radial) and leaving, it flies on a VOR radial of 090°. The radial reference changes, but the course does not. The second graphic shows us the same scenario, but with a course of 270°. Make sure you understand that: * when approaching, the aircraft is on a course of 270°, it is on the VOR radial 090°, and is on a VOR bearing of 270°. * When leaving, the aircraft is on a course of 270°, is on a VOR radial of 270°. So the VOR provides the pilot with information about the location of the aircraft in relation to the VOR station, as well as providing a magnetic bearing to or from the VOR station. [[Frequently Asked Questions#What is the difference between radial and bearing|❓]] [[Pasted image 20201228211459.png|➡]]![[Pasted image 20201228211459.png|350]] %% - [ ] #JB graphic 🛫 2023-01-17 %% It is important to notice in the above graphic that the bearing information to the VOR station is not the same as the magnetic bearing of the aircraft itself. VOR information is independent of the direction or heading of the aircraft. VOR information is always in relation to the VOR station. #### The VOR Signal %%==[[Faculty/Student/Content/C203/Master QB#Q00098|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00106|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00111|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00112|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00114|Q]]==%% VOR uses two types of [[modulation]] broadcast from two antennae to establish the radials mentioned above. - A 30 HZ [[FM|Frequency Modulated]] Subcarrier Reference Signal - broadcast from the simple central antenna - A 30 HZ [[AM|Amplitude Modulated]] Subcarrier Variable Signal - broadcast from the circular antenna array A quick note about [[subcarrier]]s. With apologies to any engineering students, the simplest explanation of subcarriers is that they are [[modulation]]s. The carrier frequency is modulated to produce a subcarrier, which is then modulated again. So in the case of the reference signal described above, the carrier frequency (the frequency we tune to) is modulated to produce a subcarrier (of 9960Hz). This subcarrier is frequency modulated at 30Hz to provide the phase information as we will see shortly. Similarly, in the case of the variable VOR signal, the carrier (the frequency we tuned to) is modulated to produce a subcarrier of 9960 Hz which is amplitude modulated at 30 Hz to produce a rotating phase signal. It is out of the scope of this course to explain the real technology here and its reasons, but suffice it to say that FM and AM subcarriers indicates that the two signals are modulated modulations. - Reference = stationary - Variable = rotating - [[Phase]] difference gives the information The reference signal is stationary, and is [[FM|frequency modulated]] at 30 Hz. Its beginning point is at 0 degrees, or north. The variable signal is rotating and is [[AM|amplitude modulated]] at 30 Hz. Its beginning point rotates and therefore provides a point of comparison between the two. The VOR receiver senses when the variable signal is pointed at the aircraft, and by comparing with the reference signal at that radial, is able to calculate which radial the aircraft is on. This radial corresponds directly with the phase difference in degrees between the two signals. So, this rotating radio signal is really only an effect. The signal itself is not rotating. But, it has the same effect. By delaying the wave progressively around the circle (adjusting the phase), it seems like the wave is spiraling out. What is important though is that the phase for these waves is different at each degree of the circle. The reference signal's phase is always the same. The comparison of the two is how we can determine which radial the aircraft is on. The reference signal and the variable signal are in phase only on the 0 degree (MN) radial. Every other radial represents one of 360 degrees of phase difference. The VOR receiver compares the [[phase]] difference between the two signals, and displays this phase difference as degrees of the compass. [[Pasted image 20201228221806.png|➡]]![[Pasted image 20201228221806.png|350]] [[Pasted image 20201228221819.png|➡]]![[Pasted image 20201228221819.png|350]] The graphic above shows that when the signal is in phase, it indicates that the aircraft is due north of the VOR station. %% - [ ] #JB graphic 🛫 2023-01-17 %% ### VOR Indications This does make things a little difficult to follow, but VOR indications can be displayed on a number of different instruments. #### Manual VOR Indications Manual VOR indications are displayed on Course Deviation Indicator ([[CDI]]) or [[HSI]] type instruments. <div style="background-color: #2a839c;"> <a title="Mysid, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons" href="https://commons.wikimedia.org/wiki/File:Horizontal_situation_indicator-en.svg"><img width="350" alt="Horizontal situation indicator-en" src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Horizontal_situation_indicator-en.svg/512px-Horizontal_situation_indicator-en.svg.png"></a></div> [[Pasted image 20201228222015.png|➡]]![[Pasted image 20201228222015.png|350]] [[Pasted image 20201228222047.png|➡]]![[Pasted image 20201228222047.png|350]] [[Pasted image 20201228222037.png|➡]]![[Pasted image 20201228222037.png|350]] There are two types of [[CDI]] display, 2 dot and 5 dot. Both have the same total of 10 degrees deviation, and is known as Full Scale Deflection ([[FSD]]). ##### About the OBS >[!aside]- Ref [[OBS|🗺️]] The Omnidirectional Bearing Selector determines around which bearing the needle will vary. If a pilot wants to approach the VOR station from due east then the aircraft will have to fly due west to reach the station. The pilot will use the OBS to rotate the compass dial until the number 27 (270°) aligns with the pointer (called the primary index) at the top of the dial. When the aircraft intercepts the 90° radial (due east of the VOR station) the needle will be centered and the [[To From indicator]] will show "To". Notice that the pilot sets the VOR to indicate the [[reciprocal]]; the aircraft will follow the 90° radial while the VOR indicates that the course "to" the VOR station is 270°. This is called "proceeding inbound on the 090 radial." The pilot needs only to keep the needle centered to follow the course to the VOR station. If the needle drifts off-center the aircraft would be turned towards the needle until it is centered again. After the aircraft passes over the VOR station the To/From indicator will indicate "From" and the aircraft is then proceeding outbound on the 270° radial. The [[CDI]] needle may oscillate or go to full scale in the "cone of confusion" directly over the station but will recenter once the aircraft has flown a short distance beyond the station. This idea that the pilot flies towards the needle is the norm for this and other systems with a similar needle variation over a centre line. #### Automatic VOR Indications Automatic VOR indications are displayed on Compass Instruments. An [[RMI]] will display an arrow in context of a [[faculty/student/references/glossary/Compass Rose|compass rose]]. [[Pasted image 20201228223639.png|➡]]![[Pasted image 20201228223639.png|350]] [[Pasted image 20201228223821.png|➡]]![[Pasted image 20201228223821.png|350]] Try each of the following scenarios to familiarize yourself with the indications for given aircraft positions. [[Pasted image 20201228223830.png|➡]]![[Pasted image 20201228223830.png|350]] ### VOR Frequencies - 108.0 to 117.95 MHz (VHF Band) - Even 100KHz The VOR system operates in the VHF frequency band , from 108.0 to 117.95 MHz. but only on non localizer frequencies. You will see why shortly. The first 4 MHz of the VOR and ILS are shared, but the VOR uses the even 100KHz frequencies. NOTE: While the operating principles are different, VORs share some characteristics with the localizer portion of [[ILS]] and the same antenna. Receiving equipment and indicators used in the cockpit can also be shared. When a VOR station is selected, on a [[CDI]] type instrument the [[OBS]] is functional and allows the pilot to select the desired radial to use for navigation. When a [[localizer]] frequency is selected, the OBS is not functional and the indicator is driven by a localizer converter, typically built into the receiver or indicator. Just to tie in what you've already learned, here is a simplified block diagram of a VOR. Notice the [[Superheterodyne|superhet]] block. You don't have to know this diagram, but have a look at how the radio signal is filtered, analyzed (compared), amplified and then sent to indicators. In the very simplest of terms, this is how radio signals drive indicators. [[Pasted image 20201228235403.png|➡]]![[Pasted image 20201228235403.png|350]] ### VOR Limitations If you refer back to the [[C203 Week 1#Radio Theory|Radio Theory lesson]] you will remember that VHF is relatively short range, up to 200 miles. Practically, the limit is the [[horizon]], or less if there are mountains or other major interferences. So VOR is prone to interference from terrain etc. and is therefore a [[line of sight]] nav aid. This may seem a disadvantage, but it is actually a good thing, as the waves are not prone to [[refraction]], or bending [[C203 Week 1#Ground Wave|as seen in lower frequency ranges]]. This ensures that the [[radial]] is accurately and directly pointing to the VOR station, so long as there is nothing in between. ## Instrument Landing System (ILS) >[!aside]- Ref [[ILS|🗺️]] ### ILS Purpose and Description %%==[[Faculty/Student/Content/C203/Master QB#Q00094|Q]]==%% - Steering guidance on landing - Required for [[IFR]] Instrument Landing Systems ([[ ILS]]) provide visual steering guidance to the pilot to align the aircraft with the runway centreline when landing. This is especially useful in poor visibility conditions, which are governed by regulations and referred to as Instrument Flight Rules ([[IFR]]). In good visibility, [[VFR]], or Visual Flight Rules apply. The ILS is a key instrument enabling flying in conditions when relying on outside visual references is not safe. #### History and Background >[!aside]- Ref [[Lorenz Beam|🗺️]] The precursor to [[ILS]] was the [[Lorenz Beam]], developed by the Germans in the 1930's. The concept was much the same, except that the pilot actually had to judge his position by listening to [[Morse Code]] in his headset. A pilot approaching the runway would tune his radio to the broadcast frequency and listen for the signal. If he heard a series of dots, he knew he was off the runway centerline to the left (the _dot-sector_) and had to turn to the right to line up with the runway. If he was to the right, he would hear a series of dashes instead (the _dash-sector_), and turned left. The key to the operation of the system was an area in the middle where the two signals overlapped. The dots of the one signal "filled in" the dashes of the other, resulting in a steady tone known as the _equi-signal_. By adjusting his path until he heard the equi-signal, the pilot could align his aircraft with the runway for landing. ILS as we know it now was invented in the 1930s and has been in use since the 1960s. #### Can be fed to AutoPilot The ILS depends on precision equipment both in the aircraft and at the runway. In modern systems, ILS information can be fed to the [[autopilot]] system to allow automated landings. Modern systems also employ Distance Measuring Equipment ([[DME]]) allowing to the pilot to know exactly where he is on his flight path. (More to follow on DME) #### Subsystems %%==[[Faculty/Student/Content/C203/Master QB#Q00117|Q]]==%% The ILS actually contains three subsystems * [[Localizer]] * [[Glideslope]] * [[Marker Beacon]] More recently, many systems include DME as an ILS component * DME Some sources categorize or organize these subsystems differently, dividing them into these functions: * Guidance information (Localizer and Glideslope) * Range Information (Marker Beacon, Compass Locators, DME) * Visual Information (Approach Lights, runway lights) ILS is a precision approach [[navigational aid]]. Without localizer and glideslope assistance, an approach may not be considered a precision approach. It provides visual guidance for lateral and vertical position, as well as distance from the runway. We will look at the component parts of an ILS, and we will do it in the same order as the pilot encounters the various components on a typical ILS landing. ## Localizer ### Localizer Purpose and Description #### Lateral guidance to runway centreline %%==[[Faculty/Student/Content/C203/Master QB#Q00118|Q]]==%% The Localizer system provides lateral (left/right) guidance to the runway centerline. This guidance typically comes in the form of a needle that moves from right to left with indication of the centerline. Information from the localizer can be sent to the autopilot system to aid in automatic landings. ### Localizer Components - Ground %%==[[Faculty/Student/Content/C203/Master QB#Q00097|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00120|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00217|Q]]==%% Ground based antenna arrays are located at the far side of the runway, and generally consist of several pairs of directional antennas. These pairs of antennas are capable of generating two [[lobes]] of RF waves which can be accurately aimed. [[Pasted image 20201229000257.png|➡]]![[Pasted image 20201229000257.png|350]] [[Pasted image 20201229000517.png|➡]]![[Pasted image 20201229000517.png|350]] The two lobes are of the same [[carrier]] frequency, but are [[Modulation|modulated]] differently. The left side lobe (as seen by the pilot) is modulated with a 90Hz tone, and the right lobe is modulated at 150 Hz. ### Localizer Components - Onboard #### Localizer receiver The localizer receiver is often combined in one component with the glideslope receiver. Like many of these systems, in larger aircraft, you can expect to see the receiver in an [[avionics bay]]. In smaller aircraft, it may be installed in the [[cockpit]]. #### Control Head The control head allows the pilot to select the localizer frequency. The control head is often combined with other systems in a single Nav Control Head. ### Localizer Theory of Operation %%==[[Faculty/Student/Content/C203/Master QB#Q00104|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00119|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00125|Q]]==%% - Measures difference in modulation levels - Drives a localizer needle in proportion The localizer receiver compares the strength of the 90 Hz and 150 Hz signals using a method called modulation depth comparison. The relative strength of the two modulated signals will be equal when the aircraft is aligned with the runway centreline. If there is a difference in signal strength, the localizer needle will deviate to provide steering commands to the pilot. A simplified explanation of this: As we have seen, amplitude of radio waves can be measured in volts. Modulation depth comparison simply measures the voltages of both of the modulated waves, and compares them. The difference in these two voltages is processed and sent to the instruments to drive the indicator. [[Pasted image 20201229000816.png|➡]]![[Pasted image 20201229000816.png|350]] Remember that [[superheterodyne]] receivers are not just for receiving broadcasting music or voice. In fact, the localizer receiver uses a superheterodyne receiver that is capable of [[Demodulator|demodulating]] both [[lobes|lobe]] frequencies to send signal voltages to the indicator. Have a look at these graphics and make sure you understand the relationship between the incoming modulated waves and the indication in the cockpit. [[Pasted image 20201229000837.png|➡]]![[Pasted image 20201229000837.png|350]] [[Pasted image 20201229001017.png|➡]]![[Pasted image 20201229001017.png|350]] [[Pasted image 20201229001031.png|➡]]![[Pasted image 20201229001031.png|350]] ### Localizer Indications %%==[[Faculty/Student/Content/C203/Master QB#Q00093|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00102|Q]]==%% [[Pasted image 20201229001059.png|➡]]![[Pasted image 20201229001059.png|350]] In this graphic, we see a [[CDI]]. The localizer needle indicates the direction the pilot should fly to. Each dot represents 1.25 degrees of deviation as specified in the [[ARINC]] Standard for the deviation bar. This is known as standard deviation for localizers or standard localizer deviaton. Variations in voltage sent by the localizer receiver deviate the needle. When sufficient voltage is present, the spring loaded warning flags are pulled out of view, indicating the instrument is operational. When the flags are visible, the instrument is not to be relied upon. The localizer needle may be found on other instruments as well: [[Pasted image 20201229001229.png|➡]]![[Pasted image 20201229001229.png|350]] [[Pasted image 20201229001236.png|➡]]![[Pasted image 20201229001236.png|350]] In this example, the localizer needle is the yellow bar. Note the terminology used (Course deviation bar). [[Pasted image 20201229001304.png|➡]]![[Pasted image 20201229001304.png|350]] ### Localizer Frequencies %%==[[Faculty/Student/Content/C203/Master QB#Q00091|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00121|Q]]==%% - 108.10MHz to 111.95MHz ([[VHF Band]]) - Odd 100KHz The localizer is assigned a small segment of the [[VHF]] band. There are 40 ILS channels. LOC carrier frequencies range between 108.10 MHz and 111.95 MHz (with the 100 kHz first decimal digit always odd, so 108.10, 108.15, 108.30, etc., are [[Localizer|LOC]] frequencies and are not used for any other purpose). #### ID Modulation ##### 1,020Hz Morse code Identifier In addition to the previously mentioned navigational signals, the localizer provides for ILS facility identification by periodically transmitting a 1,020 Hz [[Morse code]] identification signal. For example, the ILS for runway 4R at John F. Kennedy International Airport transmits IJFK to identify itself, while runway 4L is known as IHIQ. This lets users know the facility is operating normally and that they are tuned to the correct ILS. The glide slope station transmits no identification signal, so ILS equipment relies on the localizer for identification. The IATA airport code for Pearson is [[YYZ]], and we can observe aircraft on final from the front door of the campus. > [!captions] ![[Pearson Final.png]] > Final Approach to runway 24R #### Paired with Glideslope and DME %%==[[Faculty/Student/Content/C203/Master QB#Q00122|Q]]==%% Glideslope and DME frequencies are paired with the localizer frequency, and require no additional input from the pilot. ## Glideslope >[!aside]- Ref [[Glideslope|🗺️]] ### Glideslope Purpose and Description %%==[[Faculty/Student/Content/C203/Master QB#Q00123|Q]]==%% - Vertical Steering Guidance - Keeps pilot on [[Glidepath]] Once the pilot has aligned the aircraft with the runway centerline in preparation for landing, his next priority is to fly the correct glidepath down to the runway. The glideslope system provides the vertical guidance using ground based antennas, and onboard glideslope receiver and indicator. Glideslope provides visual steering indications for the pilot, and like the localizer, can be coupled to the autopilot system. ### Glideslope Components - Ground #### Glideslope Antenna %%==[[Faculty/Student/Content/C203/Master QB#Q00096|Q]]==%% The glideslope antenna is located near the [[touchdown point]] of the runway. A typical Glidepath angle is 3 degrees. ### Glideslope Components - Onboard #### Glideslope Receiver The glideslope receiver is typically in same unit as the [[localizer]] receiver. #### Indicators Like the localizer indications, glideslope can be displayed on several indicators, usually in conjunction with the localizer indications. ### Glideslope Theory of Operation %%==[[Faculty/Student/Content/C203/Master QB#Q00090|Q]]==%% Glideslope operates much the same as the localizer, but is oriented vertically. The two lobes of modulated RF are vertically separated, and are at 90Hz above the glideslope and 150Hz below the glideslope. The glideslope receiver compares the strength of the 90 HZ and 150 HZ signals using similar methods as the localizer receiver. Signal strength will be equal when the aircraft is located on the correct glidepath. If there is a difference in signal strength, the glideslope needle will deviate to provide steering commands to the crew. Glideslope radio lobes can bounce off the earth and be reflected back up. This may result in a pair of false GS lobes, always above the actual GS path. In bad conditions, it may cause a pilot to fly an incorrect glide path down to the runway. Because the typical glideslope is 3 degrees, the pilot must make a quick calculation. A 3 degree slope equates to 300ft of altitude for every nautical mile. Therefore, the pilot will check his distance from the runway. If he is, for instance, 5 NM from the runway, he will confirm that his altitude is 1500 ft. [[AGL]]. If he is not at that altitude, he immediately knows he is not on the correct glidepath. [[Pasted image 20201229002029.png|➡]]![[Pasted image 20201229002029.png|350]] [[Pasted image 20201229002036.png|➡]]![[Pasted image 20201229002036.png|350]] ### Glideslope Indications %%==[[Faculty/Student/Content/C203/Master QB#Q00092|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00103|Q]]==%% Glideslope indications that provide visual steering indications for the pilot are usually given with a horizontally oriented needle or a triangular pointer on a scale. Like the localizer, it indicates the direction the pilot should fly to. When the pilot is on the correct glideslope, the indicator is centred. Each dot represents 0.35 degrees of deviation from the glidepath. This is referred to as the standard glideslope deviation. [[Pasted image 20201229002155.png|➡]]![[Pasted image 20201229002155.png|350]] [[Pasted image 20201229002201.png|➡]]![[Pasted image 20201229002201.png|350]] [[Pasted image 20201229002216.png|➡]]![[Pasted image 20201229002216.png|350]] ### Glideslope Frequencies %%==[[Faculty/Student/Content/C203/Master QB#Q00105|Q]]==%% %%==[[Faculty/Student/Content/C203/Master QB#Q00268|Q]]==%% - 329MHz to 335MHz ([[UHF]]) The glideslope antenna at the runway transmits in the [[C203 Week 1#Aviation Radio Frequency Bands|UHF band,]] specifically in the range of 329MHz to 335MHz. The glideslope frequencies are paired with localizer frequencies, and the glideslope receiver is automatically tuned when a Localizer frequency is selected on the control head. Channel|LOC|G/S ---|------|------ 38X|110.10|334.40 38Y|110.15|334.25 40X|110.30|335.00 40Y|110.35|334.85 42X|110.50|329.60 42Y|110.55|329.45 44X|110.70|330.20 44Y|110.75|330.05 46X|110.90|330.80 46Y|110.95|330.65 Note the channel frequencies above. See how the rule that localizer frequencies are restricted to the odd 100Khz is applied, and how this doesn't mean there is only one station for each 100KHz. ## Marker Beacon >[!aside]- Ref [[Marker Beacon|🗺️]] ### Marker Beacon Purpose and Description - Progress along the [[Glidepath]] Marker beacon provides progress of the aircraft on the glide path during approach for landing. In the simplest terms, it tells the pilot via audio and visual signals how far the aircraft is from touchdown. Marker Beacon is no longer in use in Canada at all, and it's use worldwide is almost finished as well. ### Marker Beacon Components - Ground - 2 or 3 Ground transmitters The Marker Beacon consists of two or three ground transmitters located along the approach path. When only two Marker Beacon antennas are used, the inner marker is absent. * Outer Marker * Middle Marker * Inner Marker/Airways Marker [[Pasted image 20201229002435.png|➡]]![[Pasted image 20201229002435.png|350]] ### Marker Beacon Components - Onboard A Marker Beacon receiver, often with integrated lights and audio warnings will be situated most often in the cockpit. In other words, this simple device is rarely configured with a reciever in the [[avionics bay]] and a [[control head]] in the cockpit. ### Marker Beacon Theory of Operation The transmitters transmit a 75MHz modulated cone-shaped radio pattern straight up into the air. When the aircraft flies directly over, the receiver provides an aural tone of [[Morse code]] dots and dashes and a coloured indicator light on the flight deck. [[Pasted image 20201229002444.png|➡]]![[Pasted image 20201229002444.png|350]] The Outer Marker, which normally identifies the final approach fix ([[FAF]]), is situated on the same course/track as the localizer and the runway center-line, four to seven [[nautical mile]]s before the runway threshold. The Middle Marker is typically situated 1050 metres from the runway, and the inner marker is usually right at the threshold. In North America the outer marker was often combined with a non-directional beacon ([[Non Directional Beacon|NDB]]) to make a Locator Outer Marker ([[LOM]]). Aircraft can navigate directly to the location using the NDB as well as be alerted when they fly over it by the beacon. The LOM is becoming less important now that GPS navigation is well established in the aviation community. Some countries, such as Canada, have abandoned marker beacons completely, replacing the outer marker with a non-directional beacon (NDB); and, more recently, with GPS fixes. ### Marker Beacon Frequencies - As per previous graphic ### Limitations of ILS - Sensitive to Obstruction - Straight Line Approach Only Due to the complexity of ILS localizer and glideslope systems, there are some limitations. Because of the nature of the radio waves involved, based on their frequency range, localizer systems are sensitive to obstructions in the signal broadcast area, such as large buildings or hangars. Glideslope systems are also limited by the terrain in front of the glideslope antennas. If terrain is sloping or uneven, reflections can create an uneven glidepath, causing unwanted needle deflections. Additionally, since the ILS signals are pointed in one direction by the positioning of the arrays, glide slope supports only straight-line approaches with a constant angle of descent. Installation of an ILS can be costly because of siting criteria and the complexity of the antenna system. #### Back Course Modern localizer antennas are highly directional. However, usage of older, less directional antennas allows a runway to have a non-precision approach called a localizer back course. This lets aircraft land using the signal transmitted from the back of the localizer array. Highly directional antennas do not provide a sufficient signal to support a back course. In the United States, back course approaches are typically associated with Category I systems at smaller airports that do not have an ILS on both ends of the primary runway. Pilots flying a back course know to disregard any glide slope indication, and that indications for the localizer will be reversed, that is, he will have ot fly away from the needle to correct his lateral position. ![[Pasted image 20220117203857.png|350]] ## Conclusion We looked at two very complex and important avionics [[V Navigation Systemsnav systems]], [[VOR]] and [[V ILS]]. You should now know enough to understand their importance, which technology is used to accomplish this functionality, and in general terms what its components are and how it works. Don't forget to use the weekly practice quiz in [eCentennial](https://e.centennialcollege.ca/d2l/home) to make sure you are up on all of the material from this week. [[C203 Intro#Testing and Grades|You will be tested on this]] on the midterm and on the final. > # [[C203 Week 2| ◀️ ]]  [[C203 Home| Home ]]  [[C203 Week 4| ▶️ ]]               [[QR C203T SSGW03| 🌐 ]]    [[FB C203|Please Help]]