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ILS | Radioayudas IFR | — Transcript

by Mundo Aeronáutico · 3,129 words · 467 segments · language en · Watch on YouTube

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0:09Today we will talk about the ILS, its
0:11main components, and how they work. So,
0:14what is an ILS? An ILS, which stands
0:17for Instrument Landing System, is
0:20exactly what the name implies. It is a
0:23precision approach system installed on
0:25the ground that assists in approach and
0:27landing. It emits electromagnetic waves
0:31providing vertical and lateral guidance
0:33on the approach path to a runway. This
0:36is the localizer antenna of an ILS
0:38system and this is its cartographic
0:41symbol. Let’s talk now about its
0:45operating frequencies. According to
0:49Annex 10 of the International Civil
0:51Aviation Organization, the frequencies
0:54allocated for ILS localizer use range
0:57from 108.1 MHz to 111.975 MHz, using
0:59only odd decimals, since even decimals,
1:02as we said in the VOR video, are for
1:04VOR use. For the glide slope, which is
1:11another component of the ILS,
1:13ultra-high frequencies from 328.6 MHz
1:16to 335.4 MHz are allocated. These are
1:21Space Waves according to the wave
1:23propagation video, as they range from
1:2530 MHz to 3 GHz. We can recall how
1:29Space Waves propagate. For more
1:31information, you can visit the wave
1:33propagation video on this channel. Here
1:39we have the representation of the
1:41electromagnetic spectrum and we can see
1:44that the localizer frequencies ranging
1:46from 108.1 to 111.975 are in the Space
1:49Wave range. Just as the glide slope
1:52waves do. We can say that the ILS has
1:58different channels, specifically 40,
2:00which are these here. Those channels
2:04are arranged so that a localizer
2:06frequency is paired with a glide slope
2:09frequency in an orderly manner. Let's
2:15look now at what makes up an ILS system
2:17. It consists of the localizer, the
2:22glide slope, markers, compass locators
2:25or a DME, and a lighting system,
2:28whether for approach or on the runway
2:32itself. Here you can see a graphic
2:35showing the different components in an
2:37ILS. And we can group them according to
2:41their functionality. In this case,
2:43guidance functionality is provided by
2:46the localizer and the glide slope.
2:51Range or distance information is
2:54provided by marker beacons, the DME, or
2:57compass locators, and visual
3:00information can be the lights, both
3:03approach and runway lights. Let's look
3:09now at what corresponds to guidance,
3:11that is, the localizer and the glide
3:13slope. The localizer provides lateral
3:19guidance information relative to the
3:21runway centerline course. In this case,
3:25we can see the image of a localizer.
3:29The localizer approach course is known
3:31as the front course. As you can see,
3:35the front course side and the localizer
3:38antenna are located at the opposite
3:40threshold, that is, on the opposite
3:42runway end. And that is an image of a
3:46localizer antenna. Now, how does a
3:52localizer work? The antenna emits
3:55electromagnetic waves with amplitudes
3:57modulated at 90 Hz to the left of the
4:00localizer and 150 Hz to the right of
4:02the localizer. In this case, we can see
4:06in the image the representation of the
4:09runway, the localizer antenna located
4:11at the back of the runway, and we can
4:14see the modulated amplitude lobes; in
4:16this case, on the left side, the 90 Hz
4:18path and on the right side, the 150 Hz
4:21path. As a convention, we will use the
4:25colors yellow for 90 Hz and blue for
4:28150 Hz. The equipment seeks the same
4:32amount of modulation to remain aligned.
4:34That is, the aircraft seeks to have the
4:36same amount of yellow modulation as
4:38blue modulation. This will obviously
4:41lead it to the center of the runway,
4:43keeping it on the runway axis. If, for
4:46example, the aircraft receives more
4:48yellow modulation, that is, 90 Hz, the
4:49equipment will interpret that it is to
4:51the left. of the localizer; therefore,
4:54it will indicate for it to fly to the
4:55right. While if the aircraft receives
4:58more blue 150 Hz modulation, the
5:00equipment will interpret that the plane
5:02is to the right of the localizer;
5:04therefore, it will indicate for it to
5:06fly to the left to intercept it. Now
5:11let's talk about the back course. It is
5:14a particularity of the localizer signal
5:16, since the localizer antenna not only
5:18emits signals towards the approach side
5:20, that is, the front course, but also
5:22in the opposite direction, that is, the
5:24approach course of the opposite runway.
5:28We can then see the front course on the
5:30left and the back course on the right.
5:34In this case, the system is designed so
5:36that the ILS is for the front course on
5:38this side. However, the localizer
5:40signal is also radiated towards the
5:43rear, that is, the back course. We can
5:48see the modulations we had seen
5:50previously, 90 yellow and 150 blue.
5:56Let's remember that the 90 Hz yellow
5:58will indicate to the plane that it is
6:00too far to the left, while the 150 Hz
6:02blue will indicate to the plane that it
6:04is too far to the right. We can see
6:08that if an aircraft is on a standard
6:09ILS procedure and is in the yellow lobe
6:11, the equipment will indicate that it
6:13is too far to the left, meaning it
6:15should fly to the right to intercept
6:17the localizer. But let's see what
6:19happens if an aircraft is flying a back
6:21course and receives a localizer signal.
6:23If it is in the 90 Hz yellow lobe, it
6:25will continue to indicate that it is
6:27too far to the left, meaning it should
6:29fly to the right, but if it flies to
6:31the right, it will move even further
6:32away from the localizer. Therefore, we
6:35can conclude that back course signals
6:37are the inverse of ILS signals. There
6:41are several types of approaches with
6:43back course procedures, but they are on
6:46their way to disappearing, as using ILS
6:48equipment to fly a back course approach
6:50, where the signals are reversed, can
6:52be quite confusing for the crew and can
6:55pose a high flight safety risk. Now
7:02let's talk about the localizer service
7:04volume. In this case, laterally, there
7:08is a service volume of 35 degrees up to
7:1110 miles and 10 degrees between 10 and
7:1418 miles. As we can see in the image,
7:17the localizer antenna located at the
7:20back of the runway radiates its signal
7:22at 35 degrees up to 10 miles and then
7:2510 degrees up to 18 miles. An aircraft
7:28might receive a localizer signal
7:29outside these limits; however, there is
7:31a high probability that this signal
7:33will be erroneous or subject to
7:35fluctuations. Therefore, one must
7:37always ensure they are within this
7:39margin of error. This same volume also
7:43applies to the back course. That is, if
7:45we go to the rear of this runway, we
7:47can have this same service volume for
7:49the localizer signal in back course.
7:55Now, vertically, it goes from zero to
7:584,500 feet. This is in height, with
8:01zero being the elevation at which the
8:03localizer antenna is located. In this
8:07image, we can see a 3D representation
8:09of both types of service volumes, and
8:12here it reaches 4,500 feet. Now let's
8:19talk about the localizer course, since
8:21the volumes we just saw are only for
8:23receiving a localizer signal. The
8:26localizer course itself is much
8:28narrower; it is only 5 degrees. This
8:32means the instrument will give us a
8:34margin of error of 2.5 degrees on each
8:35side, which is quite small, so the
8:37reception will be quite sensitive. All
8:41localizers transmit their two or
8:43three-letter identifier, preceded by an
8:45'I', which obviously stands for ILS, in
8:47Morse code. In Jeppesen format, on the
8:52chart we can see the localizer symbol
8:54or an ILS, the type of facility. In
8:57this case, it must be clarified that it
8:59is an ILS, as it could just be a
9:01localizer. The identifier, its Morse
9:04code, the localizer frequency, in this
9:08case 111 point 9, and the localizer
9:11course 358. Now let's talk about the
9:17other component, the glide slope. This
9:19provides vertical glide path guidance.
9:22We can see a side view of the glide
9:24slope in the image. It only radiates
9:28its signal towards the front course,
9:30meaning that if we are on a localizer
9:31back course, we will not receive a
9:33glide slope signal. The glide slope
9:36frequency is paired with the localizer
9:38frequency via one of the 40 ILS
9:40channels we saw earlier. Therefore, it
9:43is not required for the pilot to enter
9:44the glide slope frequency, as entering
9:46the localizer frequency provides glide
9:48slope information. The glide slope
9:51antenna is located between 750 and 1250
9:54feet from the threshold and is offset
9:56to the side between 250 and 650 feet
9:59from the runway centerline. We can then
10:02see where the glide slope antenna would
10:05be roughly located. Let's now look at
10:12how the glide slope works. The antenna
10:15emits electromagnetic waves with
10:17amplitude modulation of 90 Hz above and
10:19150 Hz below. It is basically the same
10:23as the localizer's modulated
10:24frequencies, only these do not
10:25correspond to left or right, but up or
10:27down. As you can see in the graph, we
10:31have 90 Hz above and 150 Hz below. And
10:34the equipment will do the same; it will
10:37seek the same amount of modulation to
10:39stay on the glide path, the same amount
10:42of 90 Hz as 150 Hz. Let's now look at
10:51the glide slope projection. In this
10:54case, the projection is normally
10:56between 2.5 and 3.5 degrees. With 3
10:59degrees being optimal according to the
11:01base. We can see that it radiates
11:04exactly 1.4 degrees, meaning 0.7 above
11:07and 0.7 below, which means it will also
11:10be quite sensitive. The glide slope
11:14signal is designed to be used down to
11:16the decision height. Below this, the
11:20signal may fluctuate or show erroneous
11:22indications. If there is no published
11:25DH, then it is usable down to the
11:27threshold. Let's now look at range
11:33information, which consists of marker
11:35beacons, compass locators, and DME. In
11:39this case, we have the marker beacons.
11:43Its power is less than 3 watts and it
11:45emits electromagnetic signals modulated
11:47at 75 MHz upwards. That is to say, its
11:51signal can only be received when
11:53passing over one of these marker
11:54beacons and not anywhere else. There
11:58are three markers. Let's start with the
12:04outer marker. This indicates or marks
12:07the position where an aircraft on the
12:09localizer would intercept the glide
12:11slope, that is, the start of the ILS
12:13procedure. It usually indicates the
12:16final approach point or final approach
12:18fix, depending on the type of approach.
12:20It ranges from 4 to 7 miles from the
12:22threshold. The modulated tone, that is,
12:26the audio we will hear in the cockpit,
12:28is 400 Hz. Its identification is Oscar
12:31Mike, which stands for outer marker.
12:33Its identification color is blue, and
12:36the code we will hear is continuous
12:38dashes. We can see the position of the
12:42outer marker with respect to the runway
12:45and the ILS system. And this is the
12:48indication we will have in the cockpit,
12:50a blue light with the letter O. Now
12:57let's go with the middle marker. This
13:00indicates or marks a position
13:02approximately 3,500 feet from the
13:04threshold. If the glide path is 3
13:06degrees, the aircraft should be more or
13:08less 200 feet above the ground. It
13:11usually indicates the decision height
13:13in a Category 1 ILS approach, since in
13:15a Category 1 approach, the minimum
13:17decision height is 200 feet. The
13:21modulated tone we will hear is 1300 Hz,
13:23that is, higher pitched. Its
13:26identification is Mike Mike for middle
13:28marker. Its color is amber, and the
13:30code we will hear is dot-dash-dot-dash.
13:35That is the position of the middle
13:37marker with respect to the runway, and
13:39this is the indication we will have in
13:41the cockpit, an amber light. Let's look
13:47now at the inner marker. This indicates
13:50or marks a position where the aircraft
13:52must be at the decision height of a
13:54Category 2 or 3 approach. This is only
13:58used if the type of ILS is Category 2
14:01or Category 3. It should be found
14:04approximately 1,800 feet from the
14:06threshold, however, it depends on the
14:07decision height. The modulated tone is
14:113,000 Hz, which is quite high-pitched.
14:13Its identification is India Mike for
14:15inner marker. Its color is white, and
14:17the code we will hear is dots. We can
14:21see the position of the inner marker
14:22relative to the runway, and that is the
14:24indication we will have in the cockpit,
14:26a white light. We can see now how
14:31marker beacons work. The antenna
14:35receives them all modulated at 75 MHz,
14:37but the equipment performs a filter of
14:40400 Hz for the outer marker, 1300 for
14:42the middle marker, and 3000 for the
14:44inner marker. And we will hear these
14:49only when we pass over the marker,
14:51indicating range and distance
14:53information with respect to the runway.
14:59Now let's look at the compass locator.
15:01A compass locator is a low-power NDB,
15:04as we saw in the video on NDBs, which
15:06is less than 25 W and can be used
15:08instead of a marker beacon to mark one
15:11of these positions. An advantage is
15:14that, as it is a radio itself, it
15:15facilitates the creation and
15:17orientation of procedures, since we
15:19will not only receive the signal when
15:20we are over it, but we will also be
15:22able to navigate with it. We can see
15:26the position of a low-power NDB, which
15:28would be the compass locator coupled
15:29with an ILS system. A compass locator
15:33can be placed instead of an outer
15:35marker or middle marker. And in this
15:37case, its identification would change
15:39to Lima Oscar Mike, which is Locator
15:42Outer Marker, or Lima Mike Mike,
15:44Locator Middle Marker. Let's now see
15:49the use of a DME system coupled with
15:51the ILS. Let's remember that we already
15:53saw the DME in the video about VOR. A
15:57DME can be installed together with the
16:00glideslope antenna to provide range
16:02information and can be used to replace
16:04one or more marker beacons. As we can
16:08see, we have an ILS system with its
16:11respective markers. In this case, an
16:14aircraft passing over the marker will
16:16know it is at the final approach point
16:18of the procedure. An aircraft at the
16:21middle marker will know it is
16:23approximately 200 feet above the ground
16:25, and when it passes the inner marker,
16:27it will know it is at the decision
16:28altitude. But with a DME system, we can
16:32replace these markers solely with mile
16:34information. For example, by installing
16:38a DME antenna next to the glideslope,
16:40in the chart we can replace the outer
16:42marker with a distance; that is, when
16:43the equipment indicates 6.2 miles, it
16:45can indicate the final approach point.
16:49The same can happen with the other two:
16:51the middle marker in this case at 1.0,
16:54and the inner marker at 0.4 DME. This
16:58turns out to be much more economical,
17:00since you do not have to install three
17:02marker beacons, but only one DME
17:04antenna and perform the calculations to
17:05see the position in miles with respect
17:07to the runway. The only complication is
17:10that it must be used only when there is
17:12DME equipment on board, obviously, and
17:15not all aircraft have that type of
17:17equipment. Let's move on to the visual
17:22information that constitutes the
17:24approach lighting system, the touchdown
17:27zone lighting system, the runway
17:29centerline lights, and the runway
17:31lights. In this video, we won't cover
17:35these lights, as it would take too long
17:37, so we'll just name them. Let's now
17:42look at the ILS categories. According
17:45to the International Civil Aviation
17:47Organization, we start with Category I,
17:50which has a decision height above 200
17:53feet, a required visibility over 800 m,
17:55a runway visual range or RVR above 550
17:58m, and requires no special
18:00authorization. For ILS Category II, the
18:05decision height ranges from 100 feet to
18:07200 feet. Visibility data is not taken
18:10into account, but rather runway visual
18:12range directly. That is, the RVR. This
18:15must be greater than 300 m or 350 m for
18:18Category D, and it requires special
18:20authorization. Category IIIA has a
18:24decision height from 0 to 100 feet.
18:27Visibility data is not taken into
18:29account, and its RVR must be above 175
18:31m. It requires special authorization.
18:34Category IIIB has a decision height
18:37from 0 to 50 feet. Visibility data is
18:41not taken into account, and its RVR is
18:43less than 175 m but greater than 50 m,
18:46and it also requires special
18:47authorization. And Category IIIC, also
18:50known as Category 00, has no decision
18:53height, visibility is not taken into
18:55account, its RVR can be zero, and it
18:58requires special authorization. We can
19:03see that special authorizations require
19:05certification of the aircraft, the
19:07operator, the crew, and the airport to
19:09carry out Category II approaches and
19:11above. Now let's look at inoperative
19:17components. Some equipment for an ILS
19:19approach may be damaged. In this case,
19:22it may be degraded or simply cannot be
19:24performed. In the event that the
19:27localizer fails, the approach cannot be
19:29authorized in any way. In the event
19:32that the glide slope fails, the
19:34approach is degraded to a non-precision
19:36approach and becomes a localizer-type
19:38approach. If the ALS lights are
19:41inoperative, an ILS approach may be
19:44authorized, but by checking the
19:46corresponding minimums, as they may
19:48increase. Let's now look at the
19:52phenomena that can cause distortion of
19:54the localizer or glide slope signal. In
19:57this case, localizer and glide slope
19:59signals are space-based, as we have
20:01seen, and cannot penetrate obstacles.
20:05Therefore, signal distortion or loss
20:07may occur if there are aircraft or
20:09vehicles near the antennas. For this
20:12reason, ILS critical areas were
20:14established, which are areas intended
20:16to protect the localizer and glide
20:18slope signals to prevent these very
20:20distortions. These areas can be
20:23identified by these markings in the
20:25maneuvering area of an aerodrome. In
20:31this image, we can see how these types
20:33of markings are used to protect ILS
20:35critical areas. As you can see,
20:38although the holding point is much
20:39further ahead, to protect the critical
20:42area, a much further back holding point
20:44must be used. This one is marked with
20:46the name ILS, specifically to determine
20:48that it is an ILS critical area. As a
20:52general rule, the entry or movement of
20:54vehicles or aircraft into the ILS
20:55critical area should not be allowed if
20:57an aircraft is between the outer marker
20:59and the runway, performing an ILS
21:01approach, precisely because it could
21:03suddenly affect its signal. I hope this
21:06information has been useful to you and
21:08that you have understood how an ILS
21:10works, as well as its components and
21:12categories. Subscribe if you want more
21:14information about the aeronautical
21:15world and leave in the comments what
21:17other types of videos you would like me
21:18to make.

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