© Hal Stoen, October 6, 2000
What does "ILS" stand for?
Instrument Landing System.
What is an ILS?
In a nutshell, it is an instrument approach that gives the pilot of an aircraft visual cues on the aircraft's instruments. If the pilot follows these cues he will arrive near the approach end of the runway, usually 200 feet above the surface.
How does the ILS differ from the other types of approaches?
Generally speaking, it is the most accurate of the approaches that is available to the average civilian pilot, and allows you to descend to lower minimums. The word "minimums" refers to height (above the ground), and visibility.
The ILS offers both horizontal and vertical guidance information, whereas the VOR and NDB approaches offer horizontal (lateral) guidance only. Because it offers vertical guidance, the ILS is in the category of a "Precision Approach".
What equipment do I need in my airplane to fly the ILS?
You will need a VOR head, with glideslope display, or an HSI (Horizontal Situation Indicator). "Glass cockpits" replace these instruments with a variety of displays on CRT's (Cathode Ray Tubes). Because of the variety of displays, glass cockpits will not be referenced in this tutorial. However, the procedures remain the same. In addition, you will need a Marker Beacon receiver to indicate passage over the ground components of the ILS. An ADF or RMI, while extremely handy for orientation, is not required.
OK. what surface equipment "makes" an ILS?
1. Localizer: This is the component that provides the "left/right" guidance. Think of it as the VOR needle if you will, just more sensitive.
2. Glide Slope: This is the component that provides the "up/down" guidance. Think of it as a VOR needle laying on it's side. And, like the Localizer, it is more sensitive than the VOR display.
3. Outer Marker: This guy is in line with the Localizer's extended center line across the ground. It is normally located four to seven miles from the threshold of the runway. It transmits a signal on 75 MHz with a 400 Hz tone timed at two dashes per second. In addition to this audio tone, a blue light on the Matker Beacon receiver will flash in rhythm with the audio tone.
4. Middle Marker: Like the Outer Marker, located on an extended center line from the runway. It is normally located at the Decision Height (Missed Approach Point), on the approach, usually .5 to .8 miles from the runway threshold.
5. Approach Lights: These are the guys that John Wayne saw when he broke out on the approach into San Francisco in the movie "The High and The Mighty", along to the strains of a large orchestra. They are designed to help the pilot transition from the cockpit displays to outside visual reference for the landing. There are a various ways these are displayed. Each type has a designation, such as "ALSF-1", "ALSF-2", "SSALR", "MALSR", and so on. Suffice it to say that the "approach lights" that you see on the approach are approved by the appropriate governing authorities to do the job.
Just a second here. How do you "tune" the Marker Beacons? I don't see any radios for that purpose
Well, you can't tune them- so there! Here's the deal. All Marker Beacons transmit on the same frequency, 75 MHz. The Outer and the Middle Beacons differ in the audio tone that they emit. The Marker Beacon receiver in the aircraft is tuned to this set frequency, you as the pilot can't do any more about it. You can turn the audio off, and on some receivers you can adjust the "sensitivity" from "low" to "high". The lights associated with the Outer and Middle Markers will flash automatically. So, why aren't you bombarded with these "whistles and bells" as you fly across the country? Because they are low-powered, and once you are several thousand feet above the ground the Marker Beacon receiver will not capture the signals.
OK, what do these various components look like on the Approach Plate?
The "296 degree" remark is the heading for the Localizer.
This is the "top view". The "black elongated diamond" is the Marker itself. The "dotted concentric circles" represent the Locator (co-located NDB). The "triangle" in the middle shows that the faclity is an intersection also (usually the case).
This is the "profile view" of the Outer Marker. The center black "spike" represents the NDB, while the crosshatched area is the Marker.
Note that this is the same as the Outer Marker, except for the lack of a co-located NDB, and that there is no intersection associated with the Marker- usually the case.
This is the "profile view" of the Middle Marker.
These are not shown on the Approach Plate. They are shown on the back side of the first approach plate for an airport in the Airport Diagram.
Let's put all of this together and look at an Approach Plate, and see what some of the information that is given means to the pilot
Here is the ILS runway One Right Approach Plate for Wichita, Kansas, KICT.
NOTE: This is an old approach plate. The newer versions use color, and have other changes in the presentation. However, the content remains basically the same.
The radio information box, showing the appropriate frequencies to use for this facility.
The "Minimum Sector Altitude" information. Sometimes broken up into pieces. In this case, an altitude of 3,600 feet will provide a minimum of 1,000 feet of clearance for any obstacle that is within a 25 mile radius of the center of the circle. In this case, the center is "IC LOM", the Locator, Outer Marker (IC) for this approach.
The highest obstruction in the charted area. In this case, 2,449 feet msl.
Transition, orientation and holding information. The indicates that the Outer Marker is on the 142 degree radial from the ICT VORTAC, and 11.7 miles.
(How do we know that ICT is a VORTAC, with DME, and not just a plain VOR? See that little "D" in the box that gives the ICT frequency? That indicates that there is DME information associated with the VOR.) If you were flying this approach on your own, without radar, you could fly to the ICT VORTAC, fly outbound on the 142 degree radial 11.7 miles to the Outer Marker, and then make your Procedure Turn for the approach. This is called a "Terminal Route". The "3500" means that you could fly the route at a minimum of 3,500 feet. Oh, that "(H)"? That means that the ICT VORTAC is certified as a "High Altitude" VORTAC.
The DME facility for this approach. It is of note that the DME is not located on the approach end of the runway for this particular approach, but is instead at the far end of the runway.
A "rough" idea of the runway layout at ICT, showing major runways. A detailed runway and taxiway diagram will be on the back of the first chart for the airport.
The "information box" for the ILS. "ILS DME" tells us that we will have distance information displayed when the ILS is tuned in. "013" is the final approach course. "110.3" is the ILS radio frequency, the one that you will tune in to your Nav. receiver. "IICT" and the dots and dashes below, are the identifier for this approach. If you listen to the audio portion of the nav. signal, you will hear this Morse code identifier.
The "(IAF)" means that this is the Initial Approach Fix for this approach. "PICHE" is the name of the LOM, "332" is the frequency, and "IC" and the Morse code are the identifiers. Piche is located at the 5.5 mile DME point on the ICT ILS.
"193" is the reciprocal of the inbound course, 013.
The Procedure Turn, with suggested headings to fly it, is shown should it be necessary to execute that segment of the approach.
Terminal routes, showing ways to join the Approach. "JAMEY (IAF)" indicates that there is an intersection "off chart" to the South, that serves as an Initial Approach Fix. If you were at the JAMEY intersection, you would a heading of 334 degrees from the intersection to the "triangle" that is on the Localizer, at the 9.5 DME distance. The "triangle" represents an intersection that is unnamed. It is 13.6 miles from JAMEY to that DME fix, you would fly it at 3,000 feet, and you would not make a Procedure Turn "NoPT". Once you arrive at the 9.5 mile intersection you would join the Localizer and fly it inbound at 2,700 feet . It is 4.0 miles from the "9.5 mile intersection" to the Outer Marker, Piche.
This is the "profile view".
Let's work our way through this information. "10 NM from LOM" means that if you are making a Procedure Turn on this approach that you must complete the Turn and rejoin the Localizer within 10 miles of the LOM, Piche. You're minimum altitude during the Turn would be 3,000 feet, and after completing the Turn and headed back inbound on the Localizer you will descend to 2,700 feet. The numbers in parenthesis are the height above the ground. The LOM is 5.5 miles DME on the ICT ILS. Note that when you are flying this approach that you will be level at an altitude of 2,700 feet before you get to the OM. Also note that you will intercept the Glide Slope before you get to the OM. The "GS 2614'" means that you will be at an altitude of 2,614 feet on your Glide Slope descent when you cross the Outer Marker. The bottom line? Glide Slope intercept and Outer Marker passage do not always coincide. The "3.5" is the distance between to OM and the MM.
You will pass over the MM on the Glide Slope at "1540", 1,540 feet MSL- 220 feet AGl. Note that after crossing the MM you continue your descent for another 20 feet.The MM is not the Missed Approach Point. 200 feet above the ground, 1,520 feet on your altimeter, is the Missed Approach Point.
The "TCH 54" indicates that the Glide Slope "hits" the runway 54 feet in from the end of the runway. The "TDZE" is the altitude of the Touch Down Zone on the runway, and it is 1,320 feet MSL, whereas the airport's official elevation is "1332'", 1,332 feet MSL. If you are using a radar altimeter, you would set it for 200 feet above the TDZE, 1,520 feet, not the airport elevation. Hey, it's only a difference of 12 feet, but it could have an affect on the approach.
A printed set of instructions is given at the bottom for how to fly the Missed Approach, should you descend to minimums and not see the runway or it's environment.
The "dashed line" represents a Localizer only approach, for use when the Glide Slope is inoperative.
This is the landing minimums presentation.
It shows that you Decision Height (DH) is 1,520 feet (200 feet AGL). That is the lowest that you can descend on this approach. In a "full" ILS, with all components functioning, you will need a visibility of 2,400 feet RVR (Runway Visual Range), or 1/2 mile. "RVR" is a value received by an instrument located in the Touch Down Zone, along side the runway. The "1/2 mile" would be the visibility as reported by a qualified human observer.
If the Approach Lighting system, "RAIL or ALS out", is out of service, then higher landing minimums apply. In this case visibility increases from 1/2 mile to 3/4 mile, RVR 4,000 feet.
The rest of the box show how landing minimums are affected by having the Glide Slope (GS) out of service, and the MDA (Minimum Descent Altitude) you must use if you were shooting the ILS 1 Right approach to break off and circle to land on a different runway.
Whew! Enough book learning, let's go fly this approach
We'll do this three ways:
No radar vectors, flying it "on our own".
With radar, from an IAF, Initial Approach Fix.
With radar, with vectors to the Outer Marker.
No radar vectors, flying it "on our own"
You are in your trusty Red Baron, North of Wichita Eastbound, level at 9,000 feet enroute from your departure airport to Wichita. You tune in the Wichita ATIS, 125.15, as early as you can receive it so that you will have the current conditions and know in advance what approach you will be shooting.
"This is Wichita Mid-Continent information Bravo. Weather at Mid-Continent is 200 overcast, visibility 1/2 mile in light drizzle, fog. Wind is 360 at 5 knots, temperature 37, dewpoint 34. Altimeter 29.72. Landing and departing runway One Right. Advise on initial contact that you have information Bravo." You write this information down on your dispatch form. Center calls. "Red Baron 123, proceed direct to the Wichita VORTAC, descend to and maintain 5,000." "Direct to Wichita, we're out of nine for five, Red Baron 123." "Roger Red Baron 123, contact Wichita Approach on 126.7." "126.7, good day." "Good morning Approach, Red Baron 123 is with you, descending to 5,000. Proceeding direct to the Wichita VORTAC. Bravo." "Roger Red Baron 123. The Wichita Terminal Radar is out of service. Continue direct to the Wichita VORTAC, descend to and maintain 4,000." "Direct the VORTAC, on down to four, 123." "Roger 123. After Wichita, proceed direct Piche. Report crossing Wichita." "On down to four, direct Piche after Wichita, Red Baron 123."
A short diviation- communications failure
Notice that you have not been cleared for the approach yet. At this point your clearance limit is Piche. So, what happens if you cross the Wichita VORTAC and call Approach and they don't answer? You try and try but get no reply. Either your radios have failed, or Approach's have. Set your transponder to "7600", the "communications failure" mode. Perhaps Center will see it and advise Approach via telephone. Your clearance limit is Piche, you are not cleared to proceed any farther. Note the departure time that you recorded on your dispatch form. Let's say it was 0700 Zulu. What did you give for an enroute time when you filed your IFR? Let's say that it was 2 hours and 35 minutes. What is the time now? Let's say that it is 0900 Zulu.
You are expected to arrive over Piche inbound on the ILS at exactly 0935 Zulu. You're early. You are expected to hold at Piche, at your last assigned altitude (4,000 feet), and depart the hold so as to arrive back at Piche, established on the ILS, inbound at 0935. Wait a minute, there is no published hold procedure at Piche. Now what? Notice that the Procedure Turn is shown on the West side of the Localizer? That's the side that you would hold on, two minute legs. What if there was no Procedure Turn published, then what? Your call. Look at the Plate for any obstructions and hold "away" from them. Also, notice that in the "MSA circle" at the top of the plate that an altitude of 3,600 feet will give you 1,000 feet of clearance over any obstacle within 25 miles of Piche.
OK, but what if both the navs. and the comms. fail? Then you're SOL and on your own. There is no prescribed procedure for this situation, and it will always be a hot topic for bar talk among pilots. If the reported ceiling is adequate, you might wish to descend to VFR conditions, paying attention to charted obstructions, such as radio towers. If it's not VFR "down there", you may wish to climb to an appropriate IFR altitude and proceed to the nearest "good weather", hoping that Center realizes your problem and gets other aircraft out of your way. When flying, even if IFR, you should always know where "improving weather" is so that you can head out that way in this situation.
OK, back to the Approach
You cross over the Wichita VORTAC at 4,000 feet. Turn to track outbound on the ICT 142 degree radial. "Approach, Red Baron is over Wichita, outbound." "Roger Red Baron 123, proceed direct Piche. Descend to and maintain 3,500. You're cleared the ILS runway One Right Approach into Mid-Continent. Report Procedure Turn inbound." "Direct Piche, cleared the Approach, out of four for 3,500, we'll call the Turn inbound. 123." "Roger 123. For your information Sir, a Cessna 421B was on the Approach about 10 minutes ago and reported moderate rime icing on the Approach." Thank you, 123." You look over and verify that all appropriate ant-ice devices are turned on.
During your descent you have slowly been reducing ship's power to the proper approach settings. The ADF should be set to 332Kc to receive Pichie, and if you're doing this right the ADF needle should be pointing at the aircraft's nose, where Piche is located right now. Your Nav. One is tuned to ICT for this segment, Nav. Two should be set to the ILS. The DME on Nav. One reads 11.0, it's 11.7 DME from ICT to Piche. You should be there any second. The blue Marker light starts flashing and you hear a "dah, dah, dah" from the speaker. The ADF needle starts to swing clockwise towards the aircraft's tail.
You are at Piche. Write down the time. Turn to the right, roughly a heading of 195 degrees. Refer to the Nav. Two display that is tuned to the ILS and start tracking it outbound. Reset your Nav. radios so that your prime display, in this case the HSI, is driven by the Localizer, 110.3. Tune the other Nav. radio to the ICT VORTAC so that it will be ready in the event of a missed approach. Taking into account your groundspeed, remember that your Procedure Turn must be completed within 10 miles of the Outer Marker. Established on the Localizer outbound you turn right to 238 degrees, starting the Procedure Turn. After the Turn, you are back inbound on a heading (no wind) of 058 degrees. The Localizer needle is stuck over on the right side of the display, you haven't intercepted yet.
It's early in the morning, dark outside, 3am local time. There is a display of St. Elmo's Fire around the propeller arcs and out toward the wing tips. Suddenly there is an explosion from up in the nose area of your aircraft. "What the ....." Then you remember. Ice. Ice being slung off of the heated props, some of it hitting the nose section of the aircraft. You reach down and turn on the wing boot ice light. Only a half inch accumulation so far, not enough to cycle the boots for. It's 37 degrees at the airport, not much is going to melt off during the approach. You make a mental note to cycle the de-ice boots at the Marker Inbound.
The Localizer needle starts to come alive and wanders over towards the center of the HSI. You are intercepting the Localizer inbound. Turn left, heading 013 degrees, descend to and maintain 2,700 feet. "Approach, Red Baron 123 is the Turn Inbound." "Roger 123, report Piche please." "We'll call Piche, Red Baron 123." Now the Localizer needle is centered as you track it inbound. Level at 2,700 feet you verify your power settings for the approach and drop your first notch of flaps. The Glide Slope needle starts to come down from the top of the HSI. When it reaches the middle of the instrument, you drop the gear and start your descent towards Mother Earth. A glance at the wing boots shows about 3/4 inch of rime ice on them. You cycle the boots and the ice is carried away in the airstream. The blue OM light starts flashing. You hear a "dah, dah, dah". You reach up and switch the Marker Beacon receiver from "High sense." to "Low sense.". The light goes off along with the sound, only to return several seconds later. The ADF needle slews around from the nose to the tail.
You are at Piche, Inbound. Start the countdown clock on the panel. "Approach, Red Baron 123 is Piche Inbound." "Roger 123, contact the Tower on 118.2. Did you pick up any ice on the approach?" "About 3/4 inch of rime, 123." "Thank you, go to the Tower, have a good day Sir." "Good morning Wichita, Red Baron 123 is with you, inside the Marker." "Red Baron 123, not in sight, you're cleared to land runway One Right." "Cleared to land, 123." Through practice, you should know what power settings will give you the appropriate approach speed with a notch of flaps and the gear down. In an ideal world, if you are level as you cross the Outer Marker, dropping the gear should create enough drag to track the Glide Slope downward on the approach.
You glance out at the wing boots- no new ice. Airspeed good. On the Localizer, on the Glide Slope. A new noise appears. "Dit dah, dit dah, dit dah". You are over the Middle Marker at 1,540 feet. Twenty feet to go- seconds at best. A glow appears from in front of you. It's white, and moving away rapidly. It's the "rabbit", the sequenced strobe lights that lead in towards the end of the runway. You now have an identifiable segment of the approach enviroment, and may continue the approach. Just as suddenly the Approach Lights appear. The radar altimeter "whelps". You are at landing minimums, 200 feet above the ground.
Careful. This is where accidents happen. Transistioning from "head down" to "head up" is dangerous stuff. Fly the airplane. Look outside, look inside. No sudden control movements. Easy control input got you to this point, you shouldn't have to go throwing the airplane around now, just because you're "going visual". The runway end looms up through the mist. Look inside. Airspeed OK? Drop full flaps and land you're trusy steed. "Red Baron 123, take the first available turnoff, cleared to parking, monitor Ground point nine." Whew! Rewarding, wasn't it?
With radar, from an IAF, (Initial Approach Fix)
(We'll eliminate the details that were discussed above, just cover what's different in this type of approach.)
Center calls. "Red Baron 123, proceed direct to the Jamey Intersection. Descend to and maintain 5,000. Contact Wichita Approach on 120.6." Out of nine for five, Approach on 120.6, Red Baron 123." "Good morning Approach, Red Baron 123 is with you, just outside of Jamey, descending to 5,000, Bravo." "Red Baron 123, depart Jamey heading 334, intercept the Localizer on that heading and track it inbound. You're cleared the ILS runway One Right Approach, descend to and maintain 2,700." "Heading 334, intercept the Localizer and track it inbound, cleared the Approach, out of five point three (You're descending still, passing through 5,300 feet.) for 2,700." "Roger, 123. Contact the Tower at Piche." "Tower at Piche, 123."
You intercept the Localizer, and track it inbound to Piche. After that, it's the same as the first example- well, perhaps with a little less ice this time.....
With radar, with vectors to the Outer Marker
This is the most common scenario. The main difference in this situation is that the Outer Marker can "suddenly appear before you". It's very easy to get complacent as you are steered around by radar vectors, and possibly not be certain of where you are in relationship to the approach. "Situational Awareness" is the name of the game when flying, especially in the Approach Phase.
Use the ADF for Outer Marker orientation. Use radials off of a VOR, in this case ICT, to see where you are. Use the DME for distance. Use the RMI to cross check your position off of another VOR. Do anything and everything that you can to place yourself in the airspace and your relationship to the approach. I cannot over emphasize how important this is.
Don't grind along, blindly accepting radar vectors. Period.
This ends the tutorial on How to fly the ILS. If anything is not presented in a clear fashion, or not to your satisfaction, or if there are any errors, please contact me.
This narrative, along with aditional content, is available as a CD or an eBook.
For CD information click here. For eBook information click here.
© Hal Stoen
October 6, 2000
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