ILS Approaches

ILS approaches

What does "ILS" standfor?

Instrument Landing System.

What is an ILS?

In a nutshell, it is an instrument approach that gives thepilot of an aircraft visual cues on the aircraft's instruments.If the pilot follows these cues he will arrive near the approachend of the runway, usually 200 feet above the surface.

How does the ILS differ from theother types of approaches?

Generally speaking, it is the most accurate of the approachesthat is available to the average civilian pilot, and allows youto descend to lower minimums. The word "minimums" refersto 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 isin the category of a "Precision Approach".

What equipment do I need in myairplane to fly the ILS?

You will need a VOR head, with glideslope display, or an HSI(Horizontal Situation Indicator). "Glass cockpits" replacethese instruments with a variety of displays on CRT's (CathodeRay Tubes). Because of the variety of displays, glass cockpitswill not be referenced in this tutorial. However, the proceduresremain the same. In addition, you will need a Marker Beacon receiverto indicate passage over the ground components of the ILS. AnADF or RMI, while extremely handy for orientation, is not required.

OK. what surface equipment "makes"an ILS?

1. Localizer: This is thecomponent that provides the "left/right" guidance. Thinkof it as the VOR needle if you will, just more sensitive.

2. Glide Slope: This isthe component that provides the "up/down" guidance.Think of it as a VOR needle laying on it's side. And, like theLocalizer, it is more sensitive than the VOR display.

3. Outer Marker: This guyis in line with the Localizer's extended center line across theground. It is normally located four to seven miles from the thresholdof the runway. It transmits a signal on 75 MHz with a 400 Hz tonetimed at two dashes per second. In addition to this audio tone,a blue light on the Matker Beacon receiver will flash in rhythmwith the audio tone.

4. Middle Marker: Likethe Outer Marker, located on an extended center line from therunway. It is normally located at the Decision Height (MissedApproach Point), on the approach, usually .5 to .8 miles fromthe runway threshold.

5. Approach Lights: Theseare the guys that John Wayne saw when he broke out on the approachinto San Francisco in the movie "The High and The Mighty",along to the strains of a large orchestra. They are designed tohelp the pilot transition from the cockpit displays to outsidevisual reference for the landing. There are a various ways theseare displayed. Each type has a designation, such as "ALSF-1","ALSF-2", "SSALR", "MALSR", andso on. Suffice it to say that the "approach lights"that you see on the approach are approved by the appropriate governingauthorities to do the job.

Just a second here. How do you"tune" the Marker Beacons? I don't see any radios forthat purpose

Well, you can't tune them- so there! Here's the deal. All MarkerBeacons transmit on the same frequency, 75 MHz. The Outer andthe Middle Beacons differ in the audio tone that they emit. TheMarker 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 theaudio off, and on some receivers you can adjust the "sensitivity"from "low" to "high". The lights associatedwith 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, andonce you are several thousand feet above the ground the MarkerBeacon receiver will not capture the signals.

OK, what do these various componentslook like on the Approach Plate?

Localizer:

Glide Slope:

The"296 degree" remark is the heading for the Localizer.

Outer Marker:

Thisis 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 (usuallythe case).

Thisis the "profile view" of the Outer Marker. The centerblack "spike" represents the NDB, while the crosshatchedarea is the Marker.

Middle Marker:

Notethat this is the same as the Outer Marker, except for the lackof a co-located NDB, and that there is no intersection associatedwith the Marker- usually the case.

Thisis the "profile view" of the Middle Marker.

Approach Lights:

These are not shown on the Approach Plate. They are shown onthe back side of the first approach plate for an airport in theAirport Diagram.

Let's put all of this togetherand look at an Approach Plate, and see what some of the informationthat 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 usecolor, and have other changes in the presentation. However, thecontent remains basically the same.

Theradio information box, showing the appropriate frequencies touse for this facility.

The"Minimum Sector Altitude" information. Sometimes brokenup into pieces. In this case, an altitude of 3,600 feet will providea minimum of 1,000 feet of clearance for any obstacle that iswithin 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.

Thehighest obstruction in the charted area. In this case, 2,449 feetmsl.

Transition,orientation and holding information. The indicatesthat the Outer Marker is on the 142 degree radial from the ICTVORTAC, and 11.7 miles.

(How do we know that ICT is a VORTAC, with DME, and not justa plain VOR? See that little "D" inthe box that gives the ICT frequency? That indicates that thereis DME information associated with the VOR.) If you were flyingthis approach on your own, without radar, you could fly to theICT VORTAC, fly outbound on the 142 degree radial 11.7 miles tothe 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 certifiedas a "High Altitude" VORTAC.

TheDME facility for this approach. It is of note that the DME isnot located on the approach end of the runway for this particularapproach, but is instead at the far end of the runway.

A"rough" idea of the runway layout at ICT, showing majorrunways. A detailed runway and taxiway diagram will be on theback of the first chart for the airport.

The"information box" for the ILS. "ILS DME" tellsus that we will have distance information displayed when the ILSis tuned in. "013" is the final approach course. "110.3"is the ILS radio frequency, the one that you will tune in to yourNav. receiver. "IICT" and the dots and dashes below,are the identifier for this approach. If you listen to the audioportion of the nav. signal, you will hear this Morse code identifier.

The"(IAF)" means that this is the Initial Approach Fixfor this approach. "PICHE" is the name of the LOM, "332"is the frequency, and "IC" and the Morse code are theidentifiers. Piche is located at the 5.5 mile DME point on theICT ILS.

"193"is the reciprocal of the inbound course, 013.

TheProcedure Turn, with suggested headings to fly it, is shown shouldit be necessary to execute that segment of the approach.

Terminalroutes, 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 wereat the JAMEY intersection, you would a heading of 334 degreesfrom the intersection to the "triangle" that is on theLocalizer, at the 9.5 DME distance. The "triangle" representsan intersection that is unnamed. It is 13.6 miles from JAMEY tothat DME fix, you would fly it at 3,000 feet, and you would notmake a Procedure Turn "NoPT". Once you arrive at the9.5 mile intersection you would join the Localizer and fly itinbound at 2,700 feet . It is 4.0 miles from the "9.5 mileintersection" to the Outer Marker, Piche.

This is the "profile view".

Let's work our way through this information. "10 NM fromLOM" means that if you are making a Procedure Turn on thisapproach that you must complete the Turn and rejoin the Localizerwithin 10 miles of the LOM, Piche. You're minimum altitude duringthe Turn would be 3,000 feet, and after completing the Turn andheaded back inbound on the Localizer you will descend to 2,700feet. 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 areflying this approach that you will be level at an altitude of2,700 feet before you get to the OM. Also note that you will interceptthe Glide Slope before you get to the OM. The "GS 2614'" means that you will be at an altitudeof 2,614 feet on your Glide Slope descent when you cross the OuterMarker. The bottom line? Glide Slope intercept and Outer Markerpassage 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 MMyou continue your descent for another 20 feet.The MM isnot 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 is1,320 feet MSL, whereas the airport's official elevation is "1332'",1,332 feet MSL. If you are using a radar altimeter, you wouldset it for 200 feet above the TDZE, 1,520 feet, not the airportelevation. Hey, it's only a difference of 12 feet, but it couldhave an affect on the approach.

A printed set of instructions is given at the bottom for howto fly the Missed Approach, should you descend to minimums andnot see the runway or it's environment.

The "dashed line" represents a Localizer only approach, for use when the Glide Slopeis inoperative.

This is the landing minimums presentation.

It shows that you Decision Height (DH) is 1,520 feet (200 feetAGL). That is the lowest that you can descend on this approach.In a "full" ILS, with all components functioning, youwill need a visibility of 2,400 feet RVR (Runway Visual Range),or 1/2 mile. "RVR" is a value received by an instrumentlocated in the Touch Down Zone, along side the runway. The "1/2mile" would be the visibility as reported by a qualifiedhuman observer.

If the Approach Lighting system, "RAIL or ALS out",is out of service, then higher landing minimums apply. In thiscase visibility increases from 1/2 mile to 3/4 mile, RVR 4,000feet.

The rest of the box show how landing minimums are affectedby having the Glide Slope (GS) out of service, and the MDA (MinimumDescent Altitude) you must use if you were shooting the ILS 1Right approach to break off and circle to land on a differentrunway.

Whew! Enough book learning, let'sgo 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 "onour 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 receiveit so that you will have the current conditions and know in advancewhat approach you will be shooting.

"This is Wichita Mid-Continent information Bravo. Weatherat Mid-Continent is 200 overcast, visibility 1/2 mile in lightdrizzle, fog. Wind is 360 at 5 knots, temperature 37, dewpoint34. Altimeter 29.72. Landing and departing runway One Right. Adviseon initial contact that you have information Bravo." Youwrite this information down on your dispatch form. Center calls."Red Baron 123, proceed direct to the Wichita VORTAC, descendto and maintain 5,000." "Direct to Wichita, we're outof 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, descendingto 5,000. Proceeding direct to the Wichita VORTAC. Bravo.""Roger Red Baron 123. The Wichita Terminal Radar is out ofservice. Continue direct to the Wichita VORTAC, descend to andmaintain 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 Picheafter Wichita, Red Baron 123."

A short diviation- communicationsfailure

Notice that you have not been cleared for the approach yet.At this point your clearance limit is Piche. So, what happensif you cross the Wichita VORTAC and call Approach and they don'tanswer? You try and try but get no reply. Either your radios havefailed, or Approach's have. Set your transponder to "7600",the "communications failure" mode. Perhaps Center willsee it and advise Approach via telephone. Your clearance limitis Piche, you are not cleared to proceed any farther. Note thedeparture time that you recorded on your dispatch form. Let'ssay it was 0700 Zulu. What did you give for an enroute time whenyou 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 atexactly 0935 Zulu. You're early. You are expected to hold at Piche,at your last assigned altitude (4,000 feet), and depart the holdso as to arrive back at Piche, established on the ILS, inboundat 0935. Wait a minute, there is no published hold procedure atPiche. Now what? Notice that the Procedure Turn is shown on theWest side of the Localizer? That's the side that you would holdon, two minute legs. What if there was no Procedure Turn published,then what? Your call. Look at the Plate for any obstructions andhold "away" from them. Also, notice that in the "MSAcircle" at the top of the plate that an altitude of 3,600feet will give you 1,000 feet of clearance over any obstacle within25 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 prescribedprocedure for this situation, and it will always be a hot topicfor bar talk among pilots. If the reported ceiling is adequate,you might wish to descend to VFR conditions, paying attentionto charted obstructions, such as radio towers. If it's not VFR"down there", you may wish to climb to an appropriateIFR altitude and proceed to the nearest "good weather",hoping that Center realizes your problem and gets other aircraftout of your way. When flying, even if IFR, you should always knowwhere "improving weather" is so that you can head outthat way in this situation.

OK, back to the Approach

You cross over the Wichita VORTAC at 4,000 feet. Turn to trackoutbound on the ICT 142 degree radial. "Approach, Red Baronis over Wichita, outbound." "Roger Red Baron 123, proceeddirect Piche. Descend to and maintain 3,500. You're cleared theILS runway One Right Approach into Mid-Continent. Report ProcedureTurn 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 onthe Approach about 10 minutes ago and reported moderate rime icingon the Approach." Thank you, 123." You look over andverify that all appropriate ant-ice devices are turned on.

During your descent you have slowly been reducing ship's powerto the proper approach settings. The ADF should be set to 332Kcto receive Pichie, and if you're doing this right the ADF needleshould be pointing at the aircraft's nose, where Piche is locatedright 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 swingclockwise towards the aircraft's tail.

You are at Piche. Write down the time. Turn to the right, roughlya heading of 195 degrees. Refer to the Nav. Two display that istuned to the ILS and start tracking it outbound. Reset your Nav.radios so that your prime display, in this case the HSI, is drivenby the Localizer, 110.3. Tune the other Nav. radio to the ICTVORTAC so that it will be ready in the event of a missed approach.Taking into account your groundspeed, remember that your ProcedureTurn must be completed within 10 miles of the Outer Marker. Establishedon the Localizer outbound you turn right to 238 degrees, startingthe Procedure Turn. After the Turn, you are back inbound on aheading (no wind) of 058 degrees. The Localizer needle is stuckover on the right side of the display, you haven't interceptedyet.

It's early in the morning, dark outside, 3am local time. Thereis a display of St. Elmo's Fire around the propeller arcs andout toward the wing tips. Suddenly there is an explosion fromup 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 reachdown and turn on the wing boot ice light. Only a half inch accumulationso far, not enough to cycle the boots for. It's 37 degrees atthe airport, not much is going to melt off during the approach.You make a mental note to cycle the de-ice boots at the MarkerInbound.

The Localizer needle starts to come alive and wanders overtowards the center of the HSI. You are intercepting the Localizerinbound. Turn left, heading 013 degrees, descend to and maintain2,700 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 youtrack it inbound. Level at 2,700 feet you verify your power settingsfor the approach and drop your first notch of flaps. The GlideSlope needle starts to come down from the top of the HSI. Whenit reaches the middle of the instrument, you drop the gear andstart your descent towards Mother Earth. A glance at the wingboots shows about 3/4 inch of rime ice on them. You cycle theboots and the ice is carried away in the airstream. The blue OMlight starts flashing. You hear a "dah, dah, dah". Youreach up and switch the Marker Beacon receiver from "Highsense." to "Low sense.". The light goes off alongwith the sound, only to return several seconds later. The ADFneedle slews around from the nose to the tail.

You are at Piche, Inbound. Start the countdown clock on thepanel. "Approach, Red Baron 123 is Piche Inbound." "Roger123, contact the Tower on 118.2. Did you pick up any ice on theapproach?" "About 3/4 inch of rime, 123." "Thankyou, go to the Tower, have a good day Sir." "Good morningWichita, Red Baron 123 is with you, inside the Marker." "RedBaron 123, not in sight, you're cleared to land runway One Right.""Cleared to land, 123." Through practice, you shouldknow what power settings will give you the appropriate approachspeed 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 gearshould create enough drag to track the Glide Slope downward onthe approach.

You glance out at the wing boots- no new ice. Airspeed good.On the Localizer, on the Glide Slope. A new noise appears. "Ditdah, dit dah, dit dah". You are over the Middle Marker at1,540 feet. Twenty feet to go- seconds at best. A glow appearsfrom in front of you. It's white, and moving away rapidly. It'sthe "rabbit", the sequenced strobe lights that leadin towards the end of the runway. You now have an identifiablesegment 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 abovethe ground.

Careful. This is where accidents happen. Transistioning from"head down" to "head up" is dangerous stuff.Fly the airplane. Look outside, look inside. Nosudden control movements. Easy control input got you to this point,you shouldn't have to go throwing the airplane around now, justbecause you're "going visual". The runway end loomsup through the mist. Look inside. Airspeed OK? Drop full flapsand land you're trusy steed. "Red Baron 123, take the firstavailable turnoff, cleared to parking, monitor Ground point nine."Whew! Rewarding, wasn't it?

With radar, from an IAF, (InitialApproach Fix)

(We'll eliminate the details that were discussed above, justcover what's different in this type of approach.)

Center calls. "Red Baron 123, proceed direct to the JameyIntersection. Descend to and maintain 5,000. Contact Wichita Approachon 120.6." Out of nine for five, Approach on 120.6, Red Baron123." "Good morning Approach, Red Baron 123 is withyou, just outside of Jamey, descending to 5,000, Bravo.""Red Baron 123, depart Jamey heading 334, intercept the Localizeron that heading and track it inbound. You're cleared the ILS runwayOne Right Approach, descend to and maintain 2,700." "Heading334, intercept the Localizer and track it inbound, cleared theApproach, out of five point three (You're descending still, passingthrough 5,300 feet.) for 2,700." "Roger, 123. Contactthe 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, perhapswith a little less ice this time.....

With radar, with vectors to theOuter Marker

This is the most common scenario. The main difference in thissituation is that the Outer Marker can "suddenly appear beforeyou". It's very easy to get complacent as you are steeredaround by radar vectors, and possibly not be certain of whereyou are in relationship to the approach. "Situational Awareness"is the name of the game when flying, especiallyin the Approach Phase.

Use the ADF for Outer Marker orientation. Use radials off ofa VOR, in this case ICT, to see where you are. Use the DME fordistance. Use the RMI to cross check your position off of anotherVOR. Do anything and everything that you can to place yourselfin the airspace and your relationship to the approach. I cannotover 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 isnot presented in a clear fashion, or not to your satisfaction,or if there are any errors, please contact me.

This tutorial is available on aCD

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October 6, 2000

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