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Instrument Landing System (ILS)

The instrument landing system is known as the ILS. It enables a suitably equipped airplane to make a precision approach to a particular runway. A precision approach is one in which electronic glide slope guidance, as well as tracking guidance, is given. Each ILS is known by the airport and runway it serves, for example, the Lafayette ILS Rwy 10, in Indiana.

The instrument landing system has four main elements:

1. the localizer, which provides course guidance along the extended centerline of the runway (guidance in azimuth left or right of the extended centerline);

2. the glide slope, which provides vertical guidance toward the runway touchdown point, usually at a slope of approximately 3° to the horizontal, or 1:20 (vertical guidance above or below the glide slope);

3. marker beacons, which provide accurate range fixes along the approach path (usually an outer marker and a middle marker) are provided; and

4. approach lights, VASI (visual approach slope indicator), and other lights (touchdown zone lighting, runway lights, etc.) to assist in transitioning from instrument to visual flight.

There may be supplementary NAVAIDs available, including:

• a compass locator (NDB); and
• DME.

When a radio beacon is used in conjunction with the ILS markers, it is called a compass locator.

The outer marker may be replaced as a range marker on some ILS’s by a compass locator, a DME distance, or an ASR or PAR radar position from ATC. The middle marker, where more accuracy is required, may be replaced as a range marker on some ILS’s by a compass locator or PAR radar position from ATC (but not by a DME distance or ASR radar position). These range markers provide you with an accurate distance fix along the localizer.

A co-located compass locator and outer marker will appear on the approach chart as “LOM.” A co-located compass locator and middle marker will appear on the approach chart as “LMM.”

The ideal flight path on an ILS approach, where the localizer plane and the glide slope plane intersect, is referred to as the glide path. The word glide is really a misnomer carried over from earlier days, since modern airplanes make powered approaches down the glide path, rather than glide approaches. However, the term glide path is still used.

Since ILS approaches will often be made in conditions of poor visibility or at night, there is always associated visual information that can be used once the pilot becomes “visual” (has the runway environment in sight). This may include approach lights leading toward the runway, runway lights, touchdown lights, and centerline lights. Lighting is indispensable for night operations, but it can also be invaluable during daylight hours in conditions of restricted visibility.

There may also be a VASI situated near the touchdown zone to provide visual slope guidance during the latter stages of the approach. This, and other visual information, will assist you in maintaining a stable descent path toward the runway, where you can complete the landing.

The ILS is selected in the cockpit on the NAV/COM radio. Its cockpit display is usually the same instrument as for the VOR except that, in addition to the vertical localizer needle (CDI) that moves left and right for course guidance, there is a second needle or indicators that come into view. It is horizontal, and is able to move up and down to represent the position of the glide slope relative to the airplane. Some ILS indicators have needles that are hinged and move like wipers, others have needles that move rectilinearly. The airplane may be thought of as the center dot, and the intersection of the needles as the relative position of the glide path.

The Localizer (Centerline)

The localizer provides directional guidance along the extended centerline of the landing runway. Its transmitting antenna, which may be 60 feet wide and 10 feet high, is positioned at the far end of the runway and typically 1,000 feet beyond the end so as not to be an obstacle to airplanes taking off.

The localizer transmits a highly directional beam on a frequency in the VHF band between 108.10 and 111.95 MHz, the specific frequency being published on charts and in the Chart Supplement U.S. There are 40 localizer frequencies available, with all of them having an odd number as the first digit after the decimal point, such as 109.1, 108.3, and 110.5.

The Localizer Ground Equipment

The localizer antenna at the far end of the runway transmits two overlapping lobes of radio energy on the localizer’s carrier frequency (such as 109.9 MHz for Los Angeles International Airport ILS Rwy 25 Right). The lobe on the left hand side of the approach course is modulated at 90 Hz (previously known as the yellow sector), and the lobe on the right hand side of the approach path is modulated at 150 Hz (the blue sector). The two lobes overlap to provide a path in line with the extended centerline of the runway.

The colors blue and yellow were once painted on the localizer cockpit display, but this is not the case on modern instruments.

The transmission pattern is adjusted for each ILS so that the course width, from full-scale FLY LEFT to full-scale FLY RIGHT, is 700 feet at the approach runway threshold. Since runways are of varying lengths, and since the localizer antenna is positioned beyond the far end of the runway, the angular width of localizer beams will vary between 3 and 6 degrees to achieve the 700 feet course width at the approach threshold.

A typical angular width of the localizer course, from full-scale FLY LEFT to full-scale FLY RIGHT (peg to peg), is 5°, that is, 2.5° either side of the localizer course centerline, but for different localizers this may vary from 1.5° to 3°.

The localizer course information is accurate within the sectors shown in figure 13-6, from an altitude of 1,000 feet above the highest terrain along the course line to 4,500 feet above the elevation of the antenna site. Correct cockpit indications are assured if the airplane is in this airspace volume.

Outside this airspace, a correct localizer signal is not assured, and it is possible you may not even receive its coded ident.

The main function of the localizer is to provide azimuth guidance to an airplane on final approach to a particular runway. The signal transmitted out along the approach path is sometimes called the localizer front course.

Many localizers also transmit a back course (BC). This can be used for tracking when continuing overhead the runway and straight ahead following a missed approach, or when taking off and departing. In some countries, like the United Kingdom and Australia, the localizer back course is suppressed.

The back course of a localizer does not have an associated glide slope for a precision approach in the opposite direction, although false glide slope signals might exist. Some localizer back courses are available for a nonprecision approach in the opposite direction to the normal front course approach, in which case a LOC BC instrument approach chart is published.

Do not confuse the back course of a localizer with an ILS for the reciprocal runway, which will be a totally different installation with its own transmitting antennas. ATC will never have opposing ILS’s in service simultaneously. For instance, you would not expect to find ILS Rwy 8 Left and ILS Rwy 26 Right operating simultaneously, since they would be directing airplanes to opposing ends of the one runway.

The Localizer Airborne Equipment

Always positively identify a localizer before using it for navigation.

The localizer transmits on one of 40 frequencies in the VHF band between 108.10 and 111.95 MHz. The specific frequency is published on the relevant instrument approach chart. You can select this frequency on the VOR/ILS, and must identify the localizer by its Morse code ident before using it. The localizer ident is always a four-letter coded identifier beginning with I, “dit-dit.” Some modern radios decode and display the identifier.

Oakland ILS Rwy 11 is I-AAZ on frequency 111.9 MHz; Oakland ILS Rwy 27R is I-OAK on frequency 109.9 MHz; Cincinnati ILS Rwy 20L is I-LUK on frequency 110.9 MHz; and, as expected, the Cincinnati LOC BC 2R is the same localizer I-LUK on 110.9 MHz, since the 2L LOC BC is part of the 20R localizer. Have a look at your own Instrument Approach Procedures booklet for similar examples.

Identifying the localizer serves to identify the ILS (including the glide slope). For instance, identifying the Cincinnati 20L localizer I-LUK also identifies its glide slope. Correct identification is vital before an ILS (or any NAVAID for that matter) is used.

For the localizer to be usable, it must be identified, and there should be no red OFF flag associated with the vertical needle. If the OFF flag is visible, then the signal being received at the airplane is not sufficiently strong, and so the CDI indications will be unreliable and should not be used.

The airplane’s NAV/COM receiver, when tuned to a localizer frequency, compares the strengths of the two signals (150 Hz and 90 Hz) it receives, and produces a voltage that energizes the localizer needle in the cockpit instrument. If the 150 Hz signal is stronger (which will occur if the airplane on approach is out to the right), then a voltage is fed to the localizer needle that moves it to the left. This indicates that the localizer centerline is to the left of the airplane on approach.

If the signals are of equal strength, then the localizer needle is centered, providing an ON COURSE indication. If the 90 Hz signal predominates, then the voltage fed to the localizer needle moves it to the right, indicating that the airplane will need to move to the right to get back on centerline.

Full-scale deflection will occur when the airplane is displaced approximately 2.5° or more from the localizer centerline. This means that the CDI (with the five dots either side of center) is four times more sensitive when it is tuned to a localizer (at 0.5° per dot), compared with when it is tuned to a VOR (at 2° per dot). Full-scale deflection of the CDI selected to a localizer is 2.5° or more off the localizer centerline; full-scale deflection of the CDI selected to a VOR is 10° or more off the selected radial. Usable localizer signals may be obtained up to ±35° from course centerline, giving full-scale deflection beyond ±2.5°. Outside the protected signal volume, the OFF flag will come into view, and no ident will be heard.

Note. The angular width of a localizer beam is adjusted to provide a beam width (peg-to-peg) of 700 feet at the approach-end runway threshold for all ILS approaches. Consequently, full-scale deflection of the localizer needle can actually represent angles between 1.5° and 3°, depending on the length of the runway and the distance of the localizer antenna from the upwind end. The angular deviation per dot varies for the localizer needle, with 0.5° per dot being average.

The localizer course is a single fixed course, unlike the VOR, which gives the pilot a choice of 360 radials using the omni bearing selector (OBS). With a localizer frequency selected on the NAV/COM, the OBS has absolutely no significance, and changing it will have no effect on the indications of the CDI needle. It is good operating procedure, however, to dial in the inbound track of the localizer, using the OBS, simply as a reminder. It is also a habit that you will find useful if you happen to fly an airplane equipped with an HSI.

The localizer cockpit indicator does not provide any heading information, but only position information. It simply indicates how many degrees the airplane is displaced from the localizer course, and in which sector it is (left or right of course). A one-dot deviation on the localizer is approximately 0.5°, which is roughly equivalent to 50 feet/NM left or right of centerline.

Localizer Failure

If the localizer signal fails, then the whole ILS approach becomes unauthorized (including the glide slope), and an ILS approach in such a situation is not permitted. If only the glide slope signal fails, the localizer is still available.

Flying the Localizer

The ILS cockpit instrument is a performance instrument. It should be included in the selective radial scan when it is being actively used. Having gained that information (which, in this case, is the position and/or movement of the localizer needle), your eyes should return to the attitude and heading indicators.

Any corrections to heading to regain or maintain the localizer course can then be made with small coordinated turns on the attitude indicator. The heading indicator can be checked for heading, and the ILS cockpit indicator can be checked again for position and/or movement of the localizer needle. Concentrate on the HI and AI for your attitude flying, with an occasional glance at the CDI to see how the tracking is going. Do not chase the CDI.

The localizer beam is quite narrow, full-scale FLY LEFT to full-scale FLY RIGHT being only about 5°, and so any intercept of the localizer should be made at no more than 30°. Even when the CDI is pegged at full-scale deflection during the intercept, other NAVAIDs, such as a compass locator, if available, should be used to monitor closure with the localizer.

Once the CDI starts moving, indicating that you are approaching the centerline, turn immediately onto course and steer the localizer course ± estimated WCA. Hold this heading for a few seconds, even if the CDI needle is not centered, and then observe its position and motion, if any. Then, with gentle turns using the flight instruments, position the airplane on the localizer centerline and steer a suitable reference heading to maintain it.

Apply a wind correction angle that will keep the airplane on centerline.

The aim is to fly a heading that will maintain the airplane on centerline. If a crosswind exists, a wind correction angle will be required, and the airplane heading will differ slightly from the published inbound course of the localizer. The wind will probably weaken in strength as the airplane descends, and there will also be gusts and lulls, so periodic adjustments to heading can be expected.

On approach the CDI is a command instrument fly toward the needle.

For an airplane on approach, the localizer needle indicates which way the airplane should move to regain the centerline. If the localizer needle is to the left, then the airplane should be flown left. On approach, the CDI acts as a command instrument; to regain centerline, fly toward the needle.

You should aim to capture the localizer as soon as possible on the approach, and ensure that small deviations are corrected before they can become large deviations. An ILS approach normally requires many such heading corrections to regain and maintain the localizer centerline. This is only to be expected, because wind effect will almost certainly vary along the glide path.

The CDI needle displays angular displacement from the centerline and, because the localizer beam width narrows as the runway is approached (a bit like a funnel), it will become more and more sensitive during the descent. Heading corrections should become finer and finer, ±5° at the start of the approach, ±2° toward the end.

A typical heading bug on a heading indicator has an angular width of about 12°, or 6° either side of center. If such a heading bug is used as a heading datum on the HI, then most heading changes necessary to maintain the localizer can be contained within its angular width.

Use the rudder to fly the localizer with precision, avoid over-corrections, and maintain the LOC corrections within 2 degrees.

You should initially steer a heading that stops the needle moving, even if it is not perfectly centered, and hold that heading for a few seconds as a reference heading using the HI. Glance at the CDI to observe its position and any movement, then make gentle turns using the flight instruments to return the airplane to the localizer centerline and keep it there. Employ normal attitude instrument flying techniques using the flight instruments, with just an occasional glance at the CDI. You should aim to have the correct heading determined by the time you reach the outer marker, with the CDI centered and steady. Any tendency for the CDI to move after you have passed the outer marker can be remedied with small changes of heading, about ±2°.

When tracking inbound on the “back course,” the CDI is a non-command instrument — it has reverse sensing.

Tracking over the runway and outbound on the back course, the CDI remains a command instrument, so fly toward the needle to regain course centerline. If you reverse heading, however, the CDI becomes a non-command instrument (or has reverse sensing). When tracking outbound on a localizer front course, which is sometimes necessary when positioning the airplane for an ILS, the CDI will still indicate which sector the airplane is in (left or right of course), and will display the angular displacement from centerline as if the airplane were on approach. To regain centerline the airplane must be turned away from the CDI needle because it is acting as a non-command instrument when the airplane is flying outbound. When “flying” a non-command instrument, you must fly away from the CDI to pull it back into the center.

The situation is the same tracking inbound on a localizer back course, when the basic CDI becomes a non-command instrument. Some runways have a LOC BC nonprecision approach, based on tracking inbound on the back course of the ILS serving the opposite runway.

Some ILS indicators have a BC switch that enables the pilot to electronically reverse the signals to the CDI and, when flying inbound on a localizer back course or outbound on a front course, convert the CDI back to a command instrument. The switch needs to be reversed with each reversal of heading.

Additional tracking guidance is always useful (especially when tracking outbound on a localizer, or inbound on a back course), and in many ILS and LOC BC approaches this additional guidance can be obtained from a compass locator.

Flying the Localizer with an HSI

The horizontal situation indicator (HSI) combines a slaved compass card and CDI, providing the pilot with an excellent plan view of the airplane’s position relative to the localizer course. Even though the HSI course arrow setting does not affect the deviation of the localizer needle, the picture presented will be much more meaningful and useful if you set the inbound localizer course.

The HSI is always a command instrument.

A significant advantage of the HSI over the basic ILS indicator is that, because the course arrow and CDI move with the slaved compass card as the airplane changes heading, the HSI remains a command instrument at all times (provided you have the localizer course set), even when you are tracking outbound on an ILS or inbound on a LOC BC. Another advantage is that one instrument (the HSI) replaces two (the HI and CDI), thereby reducing the scanning workload for the pilot.

The HSI simplifies the interception of a localizer because of the clear plan view it presents to you. For instance, figure 13-13 shows the airplane steering a magnetic heading of 175° about to intercept the localizer which has a magnetic course of 200, an approximate 25° intercept. If you maintain MH 175, the CDI will center and then pass to the left of the model airplane, indicating that you have flown through the localizer. To intercept the course without flying through the radial, lead out of the turn before the CDI actually centers. A good technique is to achieve a rate of turn that keeps the top of the CDI aligned with the heading index — the faster the CDI is moving, the faster the rate of turn will have to be. You should be able to roll out exactly on course.

Note. If you accidentally set the reciprocal of the inbound localizer course, you will get reverse sensing. Always set the inbound localizer course on the HSI, then even when flying a localizer back-course approach, you will always have a command instrument. In other words, fly the back-course approach with the front course selected on the HSI.

The Glide Slope

The most suitable approach path to a runway for most aircraft to follow is a slope of 3° to the horizontal (a gradient of 1 in 20, or 5%) which intersects the runway approximately 1,000 feet in from the approach threshold. The 3° slope provides a descent of approximately 300 feet for every 1 NM traveled horizontally, which gives a reasonable rate of descent for most airplanes at typical approach speeds — 600 fpm at 120 knots groundspeed, for instance, and 450 fpm at 90 knots groundspeed — multiply GS × 5 to give rate of descent (ROD).

Some instrument approach charts show a rate of descent versus groundspeed table, specifying what rate of descent is required, at that groundspeed, to remain on the glide slope. (This is especially valuable information if the electronic glide slope fails and you are forced to fly a localizer-only approach).

The glide slope is the component of an ILS that provides vertical guidance during the approach, and it is usually adjusted to allow airplanes to precisely follow this “ideal” 3° descent path (a slightly different angle may be used for some ILS installations, e.g., 2.5°).

With a slope of 300 feet per nautical mile, you can expect a 3° glide slope to be:

• 3,000 feet HAT (height above touchdown) at approximately 10 NM to touchdown;
• 2,100 feet HAT at approximately 7 NM; and
• 1,500 feet HAT at approximately 5 NM.

The approximate altitude along the glide slope can be checked by multiplying the distance from the touchdown in miles by 300. For example, at 2 NM from touchdown the airplane should be about 600 feet above the touchdown zone elevation (TDZE). If the TDZE is 2,350 feet MSL, 600 feet HAT is indicated on the altimeter by 2,950 feet MSL. Also remember that 50 feet threshold crossing height (TCH) should be added if you are using distances from the threshold.

The Glide Slope Ground Equipment

The glide slope transmitting antenna is usually situated 750 –1,250 feet in from the runway threshold to ensure that any airplane flying the glide slope will have adequate wheel clearance over the threshold and any objects and/or terrain on approach. On some runways, the glide slope transmitting antenna may be positioned further in if there are high and restricting obstacles on the approach path. The threshold crossing height (TCH) of the glide slope is published on the ILS approach chart. The main wheels on some larger airplanes follow a much lower flight path than the glide slope receiving antenna, which could be located near the nose of the airplane or somewhere else significantly higher than the wheels.

The aim when flying a glide slope is not to touch down on the “numbers,” but to touch down in the designated touchdown zone (TDZ), near where the glide slope intersects the runway (about 1,000 feet in from the threshold).

As well as being located, on average, some 1,000 feet in from the threshold, the glide slope transmitting antenna is usually offset by 400 – 600 feet to one side of the centerline, both to avoid being an obstacle to aircraft operating on the runway, and to prevent interference with the glide slope signal by nearby aircraft on the ground. The glide slope is transmitted on an ultra high frequency (UHF) carrier wave using a similar principle to the localizer transmission (that of two overlapping lobes), but the transmission pattern is slightly more complex.

A large 90 Hz lobe overlaps a 150 Hz lobe in the vertical plane. The actual glide slope, formed where the two signals are equal, is typically inclined at 3° to the horizontal, but some glide slopes may be shallower at 2.5°, and others may be steeper at 3.5°. It may not seem much of an increase in approach angle, but a 4° slope is extremely steep, very noticeable in the cockpit and possibly difficult to maintain in some jet transport airplanes.

The overlap area of the two signals is about 1.4° thick, which means the useful signals extend 0.7° above and below the precise glide slope. The glide path is calibrated out to 10 NM, although signals can be received at greater distances.

Unfortunately, because of ground reflection of some of the transmissions, there may be more than one overlapping of the lobes, giving rise to a false glide slope. The first false glide slope may be formed at approximately 12.5° to the horizontal — well above the true glide slope. One or more false glide slopes may exist, and do not be surprised when a false on-slope indication is given in the cockpit when the aircraft could not possibly be on slope, for instance at 12,000 feet height above airport (HAA) when only 10 NM from the airport, or when maneuvering around the airport to intercept the ILS.

There will also be reverse sensing with a false glide slope, and usually the glide slope needle will oscillate, making it fairly obvious that the signal is a false one. If the localizer transmits a back course, then there will probably be false glide slope signals in that area which can cause the glide slope OFF flag to flicker in and out of view. Be prepared to recognize a false glide slope signal for what it is when you see one, and to disregard it.

False glide slopes will not occur below the true glide slope, so intercept the glide slope from below, being careful to follow the altitudes on the approach plate.

The problem of false glide slopes is easily solved if the pilot has in mind the altitude/distance relationship of the true glide slope, which is 300 feet/NM. Also, and most importantly, there is no false glide slope below the true glide slope — any false glide slopes will be above it, and will be inclined at least 10° (probably 12.5°) to the horizontal. For this reason it is recommended that you should always intercept the glide slope from below.

It is preferable, for example, to fly in from 10 NM at 2,500 feet HAA to intercept the glide slope at about 8 NM to go, than to descend steeply from above the glide slope in an attempt to intercept it. Transitions from the en route phase of flight on a published ILS approach are normally designed so that interception of the glide slope from below will occur.

The glide slope signals are usually accurate out to about 10 NM, but descent based on the glide slope indication should not be commenced until the airplane has first intercepted the localizer.

The ILS Rwy 27 at South Bend, Indiana, is designed so that an airplane over any of the initial approach fixes (IAFs) may maneuver quite comfortably to join the localizer inbound not below 2,400 feet MSL, and then intercept the glide slope from below. From LINGS IAF (initial approach fix) and GOSHEN IAF, the localizer intercept is a turn onto final course. From MISHA IAF, fly MC 092 outbound followed by a procedure turn to join MC 272 inbound.

The Airborne Glide Slope Equipment

The position of the glide slope relative to the airplane is indicated by the horizontal needle of the NAV/COM cockpit display. This needle may be hinged, and move like a wiper, or it may move up and down in a straight line. To be certain that the glide slope signal is usable, the red OFF flag must be out of view. The vertical glide slope scale on the typical ILS indicator consists of 5 dots above and below the central position, although the first dots UP and DOWN may be joined in a circle.

A unique glide slope transmission frequency is paired with each localizer frequency, so that the pilot automatically selects the associated glide slope when he or she tunes the localizer on the NAV/COM, without even knowing the glide-slope frequency.

The glide slope receiver in the airplane compares the relative strength of the two signals, producing a voltage that positions the glide slope needle. If the 90 Hz signal is stronger because the airplane is above the glide slope, then the glide slope needle moves down. This indicates that the airplane must FLY DOWN to recapture the glide slope. It is the airplane which moves to the glide slope (and not vice versa).

Conversely, if the airplane is below the glide slope, the needle will move up — indicating FLY UP to rejoin the glide slope. This does not mean the airplane must actually climb to recapture the glide slope. Flying level, or even just reducing the rate of descent, as the airplane flies toward the runway may be sufficient.

Do not allow the aircraft to go below the glide slope by more than half the full-scale FLY UP deflection. Go around.

A full-scale FLY UP indication means the airplane is 0.7° or more below the glide slope. Deviation from the glide slope is referred to in terms of dots rather than degrees, there being 5 dots up and 5 dots down on the instrument.

DA is a specified altitude (expressed in feet above MSL) in an IAP, at which the pilot must decide whether to initiate an immediate missed approach or continue the approach.

DH is a specified altitude (in feet AGL) in an IAP, at which the pilot must decide whether to initiate an immediate missed approach or continue the approach.

Keep the airplane right on glide slope, to the best of your ability, and do not exceed more than one-half full-scale FLY UP deviation below slope to retain adequate obstacle clearance toward the end of the approach. Half-scale FLY UP puts the airplane 0.3 or 0.4° below slope, which is significant, since the glide slope is inclined at only about 3° to the horizontal, and full-scale deviation is 0.7° below this.

As a general rule, make a strong effort to stay right on glide slope throughout the approach. A full-scale FLY DOWN indication means the airplane is 0.7° or more above the slope.

Full-scale deflections once the ILS approach has been commenced are not acceptable, since the deviation from slope is at least 0.7°, and it could be even more! There is no indication of just how far the airplane is above or below slope when the glide slope needle is fully deflected.

The typical 0.7° full-scale deviation (above or below the ideal 3° glide slope) is equivalent to about 70 feet per nautical mile from touchdown, which is a vertical deviation in feet from the glide slope of:

• 700 feet at 10 NM;
• 350 feet at 5 NM;
• 210 feet at 3 NM;
• 140 feet at 2 NM;
• 70 feet at 1 NM; and
• a few feet at the runway threshold.

From peg-to-peg on the glide slope is 1.4°; peg-to-peg on the localizer is typically 5°; peg-to-peg on the VOR is 20°. Thus the glide slope needle is 3 times as sensitive as the localizer needle, and 12 times as sensitive as a VOR needle.

The glide slope signal is only approved for navigation down to the lowest authorized decision height (DH) or decision altitude (DA) for that particular ILS, and any reference to glide slope indications below that altitude must be supplemented by visual reference to the runway environment. A Category I ILS is approved for use down to DH 200 feet HAT, a Category II ILS is approved for use down to DH 100 feet HAT, and a Category III ILS is approved for use down to DH 0 feet HAT (requiring sophisticated equipment and highly trained pilots).

If the glide slope fails, but not the localizer, then you may still be permitted to carry out a nonprecision localizer approach, without electronic slope guidance, using the localizer for guidance in azimuth, and using range markers (such as the marker beacons, DME distances or a compass locator) for descent to suitable altitudes which will be marked on the profile part of the instrument approach chart.

Referring back to the South Bend ILS Rwy 27 profile, you may cross the SB LOM not below 2,000 feet MSL and, for a straight-in approach to runway 27 in instrument conditions, descend further:

• for a precision ILS approach, using the electronic glide slope, down to a decision altitude (DA) of 974 feet MSL; or
• for a nonprecision localizer approach, without electronic slope guidance, down to a minimum descent altitude (MDA) of 1,200 feet MSL.

If only the full ILS procedure is approved for a particular runway, and a localizer only approach without the use of a glide slope is not authorized, then the chart will carry the warning LOC ONLY N/A.

Flying the Glide Slope

Flying the glide slope is similar to flying straight-and-level, except that the aim is to keep the airplane on a constant descent plane, rather than on a level plane at constant altitude. In level flight, the altimeter is checked regularly to ensure altitude is being maintained; during an ILS, the glide slope needle is checked regularly to ensure that the desired slope is being maintained.

The typical 3° glide slope requires a loss of altitude of 300 feet per nautical mile which:

• at a groundspeed of 60 kt (1 NM/minute) requires a rate of descent of 300 fpm;
• at a groundspeed of 90 kt (1 NM/minute) requires a rate of descent of 450 fpm;
• at a groundspeed of 120 kt (2 NM/minute) requires a rate of descent of 600 fpm.

Notice that a quick method of estimating the required rate of descent for an ILS is simply 5 × groundspeed. By estimating your groundspeed, and then flying an appropriate rate of descent on the VSI, you will go close to holding the glide slope without even looking at the ILS indicator.

For instance, an approach speed of 90 KIAS into a 20-knot headwind will result in a groundspeed of 70 knots, so the correct rate of descent to hold glide slope will be (5 × 70) = 350 fpm. If the headwind decreases, your groundspeed will be greater for the same airspeed, and so you would require a higher rate of descent to hold slope. Periodically refer to the glide slope needle, and adjust the rate of descent as required to hold the glide slope.

The ILS indicator is a performance instrument. It should be included in the selective radial scan when information from it is desired. Having gained that information (which, in this case, is the position and/or movement of the glide slope needle), your eyes should return to the attitude indicator. Any corrections to regain or maintain the glide slope can then be made with a small pitch attitude change on the AI. The ILS indicator can then be checked again for position and/or movement of the glide slope needle.

Hold the glide slope with small pitch attitude changes; this bracketing technique also applies to maintaining the localizer.

Hold the glide slope with small pitch attitude changes. A process similar to bracketing track is used to regain and then maintain the glide slope, although in this case it is pitch attitude that is altered slightly, rather than heading.

If, for instance, the airplane goes below glide slope while a particular pitch attitude is held, then it should be raised slightly and held until the glide slope is regained. Once back on slope, the pitch attitude can be lowered slightly (but not quite as low as before), so that the glide slope is maintained.

Hold airspeed with power.

Hold airspeed with power. There is also a target airspeed to be achieved on an ILS approach and, as in level flight, airspeed can be controlled with power. With pitch attitude changes to regain and maintain glide slope, small airspeed changes will occur. Fluctuations of ±5 knots are normally acceptable, but any trend beyond this should be corrected by a power alteration. Typically 1 inch MP or 100 RPM is sufficient, although greater power changes may be required in strong and gusty wind conditions or in windshear.

Maintaining glide slope and airspeed is one sign of a good instrument pilot. Flight path and airspeed (in other words the performance of the airplane) are controlled by attitude and power on an ILS approach. If you have a good scan and quick response, then small deviations from the glide slope will be corrected with a small pitch change immediately, and will not develop into large deviations which might require a power adjustment as well.

Flying the glide slope involves energy management. If the airplane is slightly below glide slope and slightly fast, then the excess speed can be converted to altitude (or to a reduced rate of descent) by raising the pitch attitude on the AI, and flying up to regain slope. Conversely, if the airplane is above glide slope and slightly slow, the pitch attitude on the AI can be lowered slightly, and the airplane flown down to regain glide slope, possibly with a small speed increase.

• Hold glide slope with pitch attitude on the AI.
• Hold airspeed with power.

Since it displays angular displacement, the glide slope needle will become more accurate and more sensitive as the airplane flies closer to the runway. Therefore, corrections on the attitude indicator to hold glide slope should become finer and finer as the runway is approached.

Marker Beacons

ILS marker beacons transmit a highly focused vertical signal pattern, often described as elliptical or fan-shaped, which can only be received by an airplane as it passes directly overhead. Because the radio energy is transmitted upward, it is not possible to track to a marker beacon (unlike an NDB or compass locator whose energy is transmitted in all directions). A typical ILS has two markers positioned along the localizer to provide range (or distance) check points. They are:

• the outer marker (OM) at between 4 and 7 NM from the runway threshold; and
• the middle marker (MM) at 3,500 feet (0.6 NM) from the runway threshold.

Both markers operate on the same VHF frequency of 75 MHz, but each provides a different aural Morse code identification. There is no interference between the signals because their transmission volume is upward and very localized.

The airborne equipment consists of a marker receiver which indicates passage of the airplane over a marker by a light flashing in the cockpit and an aural Morse code ident. You can hear the ident through the headset or speaker, and see the light flashing (one of three color-coded lights on the instrument panel). You do not have to make any specific selection in the cockpit to receive the marker beacons, other than have the marker beacon switch ON.

The outer marker (OM) is located between 4 and 7 NM from the runway threshold. The airplane, if it is on glide slope, should therefore be at approximately 1,400 feet HAT as it passes overhead the OM. The precise MSL altitude crossing the OM is specified on the profile diagram of the particular ILS, and you should check this on the altimeter as the airplane passes over the OM.

The cockpit indications of passage over the outer marker are:

• a continuous aural series of low-pitched (400 Hz) dashes transmitted at two per second (-dah-dah-dah-dah-dah-dah-dah-); and
• a flashing blue (or aviation purple) light synchronized with the aural “dah-dahs.”

The middle marker (MM) is located approximately 3,500 feet (0.6 NM) from the landing threshold, where the glide slope is approximately 200 feet HAT (height above touchdown). This is near the DH and missed approach point (MAP) for the ILS approach. The middle marker crossing altitude may or may not be specified on the charts, since at this stage in the approach the pilot may be visual, depending on the particular approach minimums.

The cockpit indications of passage over the middle marker are:

• an aural series of alternating medium-pitched (1,300 Hz) dots and dashes transmitted at six per second (-dah-dit-dah-dit-dah-dit-dah-dit-); and
• a flashing amber light synchronized with the aural dah-dits.

Some ILS’s have an inner marker (IM) between the middle marker and the landing threshold that has an aural “-dit-dit-dit-dit-” signal at 3,000 Hz (high-pitched) and 95 dot/dash combinations per minute, and a synchronized flashing white light.

Some localizer back courses have a back course marker (BCM) that has an aural “dit-dit dit-dit dit-dit” signal, and a synchronized flashing white light. The BC marker is used to indicate the LOC BC final approach fix (FAF).

The marker beacon signals increase in strength fairly quickly as the airplane nears the marker beacon, remain very strong for a number of seconds, and then quickly fade away as the airplane moves further along the approach. Many airborne receivers have a HIGH/LOW sensitivity switch, LOW sensitivity giving a much narrower vertical pattern. For instrument approaches, the sensitivity switch is normally set to HIGH, because the airplane will be at a low level during the instrument approach, and the marker beacon signal will only be heard and seen for a few seconds.

Other Means of Checking Glide Slope

Not all ILS installations have an outer marker and/or middle marker. For example, the Hayden, Colorado, ILS/DME Rwy 10 has neither. The glide slope, however, can be checked at the FAF at 7.8 DME from the I-HDN DME (automatically selected along with the ILS on the NAV/COM). If you are exactly on glide slope at 7.8 DME, the altimeter should read close to 8,608 feet MSL.

The DME can be helpful in providing approximate slope guidance, or protection from underlying obstructions, if the electronic glide slope is not working or is not part of the approach. For example, the localizer back course approach at Tucson International, Arizona, LOC/DME BC Rwy 29R, has a number of DME/altitude restrictions.

Descent from 8,000 feet MSL may be commenced at 20 DME using the I-TUS localizer back course and DME, followed by an approach slope:

• not below 7,200 feet until 13.5 DME;
• not below 6,100 feet until 9.5 DME;
• not below 4,800 feet until 5 DME, the final approach fix (FAF);
• not below 3,600 feet until 2 DME; and
• not below MDA 3,120 feet until visual, otherwise a missed approach at 0.3 DME.

Approach Lights and Other Lights

The aeronautical lighting facilities provided at an airport that can assist a pilot to maneuver the airplane in conditions of poor visibility or at night consist of:

• approach lighting;
• a visual approach slope indicator (VASI);
• touchdown zone lighting; and
• runway edge lighting.

Approach Light Systems (ALS)

At many airports, the approach light system (ALS) extends out from the approach end of the runway to well beyond the physical boundaries of the runway, possibly into forested or built-up areas. Approach lights do not mark the boundaries of a suitable landing area — they simply act as a lead-in to a runway for a pilot on approach to land. ALS lighting is a standardized arrangement of white and red lights, consisting basically of extended centerline lighting, with crossbars sited at specific intervals back along the approach path from the threshold, out to a distance of:

• 2,400 – 3,400 feet for precision instrument approach runways; or
• 1,400 –1,500 feet for nonprecision instrument approach runways.

Approach light systems assist you to transition from instrument flight to visual flight for a landing. In minimum visibility conditions at the decision height, for example, visibility ½ statute mile (2,400 feet), the approach lights might be the only part of the runway environment that you can see — the runway and the VASI still being more than ½ mile away — yet you may continue with the approach.

The approach lighting provides you with a visual indication of how well the airplane is aligned with the extended runway centerline (lateral guidance), as well as helping you to estimate the distance the airplane has to fly to touchdown during the latter stages of the instrument approach. This is especially useful in conditions of low visibility. In situations where no visible horizon exists, the approach lights can also assist you to visually judge the bank attitude of the airplane.

Particulars of airport lighting are shown in the instrument approach procedures (IAP) publications.

There are various types of approach light systems in use, the sophistication of the system depending on the importance of the airport and the frequency and type of operations. Some typical precision instrument runway ALS’s are shown in figure 13-28.

Some approach lighting systems include sequenced flashing lights (SFL), or runway alignment indicator lights (RAIL), which appear to the pilot as a ball of white light traveling toward the runway at high speed (twice per second) along the extended centerline.

The runway threshold is marked with a row of green lights, and some runway thresholds have flashing strobes either side to act as runway end identifier lights (REIL).

• MALSR is a medium intensity approach light system (MALS) with runway alignment indicator lights.
• Touchdown zone lighting consists of two rows of transverse light bars located symmetrically about the runway centerline, normally at 100-foot intervals. The basic system extends 3,000 feet along the runway.
• RAIL consist of sequenced flashing lights which are installed only in combination with other light systems.
• REIL provide rapid and positive identification of the approach end of a particular runway.

The view from the cockpit approaching a typical precision instrument runway in poor conditions is shown in figure 13-29.

Visual Approach Slope Indicator (VASI)

The MDA intersects the VASI glide slope.

In conditions of poor visibility and at night, when the runway environment and the natural horizon may not be clearly visible, it is often difficult for a pilot to judge the correct approach slope of the airplane toward the touchdown zone of the runway. A number of effective visual slope indicators have been invented to assist a pilot to stay on the slope in this situation; lateral guidance is provided by the runway, the runway lights or the approach light system.

Two-Bar VASI

Remember: Red over white: you’re all right.

White over white: you’re high as a kite.

Red over red: you’re probably dead.

The typical two-bar VASI has two pairs of wing bars extending outboard of the runway, usually at 500 feet and 1,000 feet from the approach threshold. It is sometimes known as the red/white system, since the colors seen by the pilot indicate right on slope, or too high or too low. The pilot will see:

• all bars white if high on approach;
• the near bars white and the far bars red if right on slope; and
• all bars red if low on slope.

During the approach, the airplane should be maintained on a slope within the white sector of the near bars and the red sector of the far bars. If the airplane flies above or below the correct slope, the lights will change color, there being a pink transition stage between red and white.

The plane of the VASI approach slope only provides guaranteed obstacle clearance in an arc 10° left or right of the extended centerline out to a distance of 4 NM from the runway threshold, even though the VASI may be visible in good conditions out to 5 NM by day and 20 NM by night. Before using VASI information, the airplane should be within this arc, and preferably aligned with the extended runway centerline. In general, an approach descent using VASI should not be initiated until the airplane is visually aligned with the extended runway centerline. On instrument approaches, once the VASI comes into view you may use it to adjust your approach path.

There are other operational considerations when using the red/white VASI. At maximum range, the white bars may become visible before the red bars, because of the nature of red and white light. In haze or smog, or in certain other conditions, the white lights may have a yellowish tinge about them.

Do not begin a VASI descent until the airplane is visually aligned with the extended centerline.

When extremely low on slope, the two wing bars (all lights red) may appear to merge into one red bar. At close range to the threshold this would be a critical situation with respect to obstacle clearance, and require urgent pilot action.

Some VASI systems use a reduced number of lights, in which case they may be known as an abbreviated VASI or AVASI.

Three-Bar VASI

The three-bar VASI has an additional bar at the far end, intended to assist the pilots of long-bodied airplanes such as the Boeing 747 or the Airbus A300. The approach slope guidance given by any VASI depends on the position of the pilot’s eyes. Since the wheels of an airplane with a very long fuselage will be well below the pilot’s eyes, it is essential that the eyes follow a parallel but higher slope to ensure adequate mainwheel clearance over the runway threshold. The additional wing bar farther down the runway makes this possible.

Pilots of such airplanes should use the second and third wing bars and ignore the first. When the pilot’s eyes are positioned on the correct slope for a long-bodied airplane, he or she will see the top bar red, the middle bar white (and ignore the lower bar which is also white).

Pilots of smaller airplanes should refer to only the two nearer wing bars and ignore the more distant wing bar, which is for large airplanes. On slope, the indications should be (top bar red and ignored), middle bar red and lower bar white.

Precision Approach Path Indicator (PAPI)

PAPI is a development of the VASI and also uses red/white signals for guidance in maintaining the correct approach angle, but the lights are arranged differently and their indications must be interpreted differently. PAPI has a single wing bar which consists of four light units on one or both sides of the runway adjacent to the touchdown point. There is no pink transition stage as the lights change from red to white.

If the airplane is on slope, the two outer lights of each unit are white and the two inner lights are red. Above slope, the number of white lights increase, and below slope the number of red lights increase. The PAPI will provide safe obstruction clearance up to 3.4 NM from the runway threshold and 10° either side of the centerline.

Pulsating Visual Approach Slope Indicator (PVASI)

PVASI consists of a single light unit positioned on the left side of a runway adjacent to the touchdown point, which projects three or four different “bands” of light at different vertical angles, only one of which can be seen by a pilot on approach at any one slope position. The indications provided by a typical PVASI are:

• well above glide slope: fast-pulsing white;
• above glide slope: pulsing white;
• on glide slope: steady white (or alternating red/white for some systems);
• below glide slope: pulsing red;
• well below glide slope: fast-pulsing red.

Tri-Color VASI

The tri-color VASI is a short-range visual slope aid (½ mile by day, 5 miles by night), and consists of a single-light unit that indicates:

• amber if above slope;
• green if on slope; and
• red if below slope.

T-VASI

The T-VASI is a system that has a horizontal bar of white lights either side of the runway aiming point. If the airplane is right on slope, you will only see these lights. If you are high on slope, single lights will appear above this bar, forming an inverted-T, and indicating FLY DOWN. If you are low on slope, single lights will appear below the bar, forming a T, and indicating FLY UP. The number of vertical lights give an indication of how far off slope you are. If you are extremely low, the lights turn red.

Runway Lighting

Runway lighting defines the boundaries of the actual landing area, and some systems provide you with distance-down-the-runway information as well.

Runway Edge Lights

Runway edge lights outline the edges of runways during periods of darkness or restricted visibility. They are classified according to the intensity or brightness they are capable of producing:

• HIRL: High Intensity Runway Lights;
• MIRL: Medium Intensity Runway Lights;
• LIRL: Low Intensity Runway Lights.

Runway edge lights are white, except on instrument runways where yellow replaces white for the last 2,000 feet (or last-half on runways shorter than 4,000 feet), to form a caution zone for landings in restricted visibility. When the pilot sees the white edge lights replaced by amber, he or she has some idea of how much runway is left for stopping.

In-Runway Lighting

Some precision approach runways have additional in-runway lighting embedded in the runway surface consisting of:

• touchdown zone lights (TDZL): bright white lights either side of the runway centerline in the touchdown zone (from 100 feet in from the landing threshold to 3,000 feet or the half-way point, which ever is the lesser);
• runway centerline lighting system (RCLS): flush centerline lighting at 50 feet intervals, starting 75 feet in from the landing threshold to within 75 feet of the stopping end; RCLS also includes runway remaining lighting, where the centerline lighting seen by a stopping airplane is:
  • initially all white;
  • alternating red and white from 3,000 feet-to-go point to 1,000 feet-to-go;
  • all red for the last 1,000 feet;
• taxiway lead-off lights: alternate green and yellow from runway centerline to runway holding position; expedites movement of aircraft from runway; and
• land and hold short lights: used to indicate the hold short point on certain runways which are approved for land and hold short operations (LAHSO), and they consist of a row of pulsing white lights installed across the runway at the hold short point.

Runway End Lights

The runway end lights show green to aircraft on approach and red to airplanes stopping at the far end.

Runway End Identifier Lights

Runway end identifier lights (REIL) consist of a pair of synchronized white flashing lights located each side of the runway threshold at the approach end. They serve to:

• identify a runway end surrounded by many other lights;
• identify a runway end which lacks contrast with the surrounding terrain; and
• identify a runway end in poor visibility.

Taxiway Lights

While not directly associated with a precision approach, it does help if you can exit the runway onto a taxiway with confidence. Taxiways are lighted in one of two ways for the guidance of pilots with either:

• one line of centerline green taxiway lights; or
• two lines of taxiway blue edge lights.

At some airports, there is a mixture of the two types, centerline green on some taxiways, and blue edge on others. At certain points on the taxiway, there may be red stop-bars installed, to indicate the position where an airplane should hold position, for instance before entering an active runway.

Runway Status Lights (RWSL)

This enhanced advisory system is composed of two features: runway entrance lights (REL) and takeoff hold lights (THL). RWSL is a fully automated system that provides runway status information to pilots and surface vehicle operators to indicate when it is unsafe to enter, cross, or takeoff from a runway. The system is installed at select airports across the U.S. to assist in preventing runway incursions. See figure 13-40.

Control of Lighting Systems

The approach lights and runway lights at an airport are controlled by:

• the control tower personnel (when the tower is active);
• the FSS, at some locations where no control tower is active (but this FSS function is gradually being eliminated); or
• the pilot (at selected airports).

The pilot may request ATC to turn the lights on (or off), or to vary their intensity if required. On a hazy day with restricted visibility, but with a lot of glare, maximum brightness might be necessary; on a clear dark night, a significantly lower brightness level will be required. At many non-towered airports, and when ATC facilities are not manned, airborne control of the lights is possible using the radio. The Chart Supplement U.S. specifies the type of lighting available, and the radio frequency used to activate the system.

To use an FAA-approved pilot-controlled lighting system, simply select the appropriate VHF frequency on the NAV-COM, and depress the microphone switch a number of times. A good technique involves keying the mike 7 times within 5 seconds, which will activate the lights at maximum intensity, and then subsequently keying it a further 5 or 3 times for medium or low intensity respectively, if desired.

Don’t get caught in the dark! All pilot-controlled lighting operates for 15 minutes from the most recent transmission.

All pilot-controlled lighting operates for 15 minutes from the time of the most recent transmission. If pilot-controlled lights are already on as you commence an approach, it is good airmanship to reactivate them and thereby ensure availability for the duration of the approach and landing.

Precision Instrument Runway Markings

To assist pilots transitioning to a visual landing at the conclusion of a precision instrument approach, precision instrument runways have specific markings.

A displaced threshold on an instrument runway is indicated by arrows in the middle of the runway leading to the displaced threshold mark. The runway edge lights to the displaced threshold appear red to an airplane on approach, and to an airplane taxiing to the displaced threshold from the absolute end of the runway. They appear white when taxiing back from the displaced threshold toward the absolute end of the runway. The green runway end lights seen on approach to a runway with a displaced threshold are found off the edge of the runway.

The runway surface with arrows to the displaced threshold is available for taxiing, takeoff and landing roll-out, but not for landing. The initial part of this runway is a non-touchdown area. If chevrons rather than arrows are used to mark the displaced threshold, then the surface is not available for any use, other than aborted takeoff from the other direction.

A precision instrument runway will contain a designation, centerline, threshold, aiming point, touchdown zone, and side strips as seen in figure 13-42. Runway threshold strips can be configured in two ways. Four solid strips on either side of the centerline or configured as such that the number of strips correlates to the width of the runway (table 13-1). The runway aiming point markers are large rectangular marks on each side of the runway centerline usually placed 1,000 feet after the threshold and serve as a visual aiming point for the pilot. Touchdown zone markers identify the touchdown zone for landing operations, providing coded distance information in 500 foot intervals and shown as either one, two, or three vertical stripes on either side of the centerline.

Inoperative ILS Components

If some component of an ILS, or a visual aid, is inoperative (say, approach lighting), then higher minimums may be required. This is specified in the Inoperative Components or Visual Aids Table in each FAA Terminal Procedures book. If more than one ILS component is inoperative, use the highest minimum required by any single unusable component.

ILS glide slope inoperative (or “GS out”) minimums are published on FAA instrument approach charts as localizer (LOC) minimums.

Flying a Typical ILS

The relevant instrument approach procedure (IAP) chart should be checked for currency, and thoroughly studied before commencing the approach. Briefing an approach is the process of identifying the key elements of the procedure, such as missed approach, minimums, and inbound course. A standard practice for professional pilots, the approach briefing can enhance the safety of any instrument landing procedure. Even though the chart can be referred to during the actual approach, it is helpful to build up an overall view of where the airplane is and what path it will follow. As an example, the published FAA Burbank-Glendale-Pasadena ILS RWY 8 chart (plan and profile) follows, with a sketch (figure 13-45) of how the approach will be flown.

The appropriate minimums should be determined. For a straight-in approach on Runway 8 using the full ILS (S-ILS 8), the DA/DH for a Category A airplane (a typical light aircraft) is DA 977 feet MSL, with a visibility or runway visual range (RVR) of 5,000 feet (1 SM) being required to land. If the electronic glide slope is not available, and the approach is made using the localizer only without the glide slope (S-LOC 8), the minimums increase to a minimum descent altitude (MDA) of 1,140 feet MSL, with 1 SM visibility required for landing. To circle and land on another runway, the minimums are further raised to 1,220 feet and 1 SM.

The missed approach procedure should always be reviewed and alternative action planned if there is any doubt that a successful landing can be made. Low clouds fluctuating around the decision height, poor visibility, heavy rain, or anything that might prejudice your arrival, should lead you to consider alternate airports.

There is always a (remote) possibility that an essential ground aid required for the landing will become unserviceable (caused by a lightning strike or flooding during a storm, for instance).

The fuel situation must be considered, and the minimum fuel on board required for diversion should be calculated. Allow for reserves. Is there fuel enough for more than one approach before diverting? How much fuel is available for holding? Is the weather at the alternate airport still suitable for an approach? Prepare for the approach well before reaching the airport, so that, once there, you can devote sufficient attention to flying the ILS approach.

Track to the airport following the normal route and using the normal en route tracking aids, maintaining the appropriate altitude. The minimum safe altitudes within 25 NM of VINEE compass locator (UR) are quite high, up to 9,100 feet MSL in the northeast sector, but ATC may clear you to lower altitudes and provide radar vectors to expedite your arrival. All clearances, headings, altitudes and pressure settings passed by ATC should be repeated. All NAVAIDs must be identified before being used.

If a holding pattern has to be entered, then plan to use the correct entry procedure based on the airplane’s heading when it reaches the holding fix (see figure 13-46). See Chapter 28 for more information on holding and pattern entries.

“Stacking” airplanes in holding patterns until a slot on the ILS becomes available is common during busy periods at major airports. As each airplane departs the bottom of the stack and proceeds into the ILS, the other airplanes can be cleared down one at a time. This will be the procedure used if ATC informs you that “timed approaches are in progress.”

In some instrument approach procedures, a DME arc may be flown to position an airplane on an ILS (figure 13-47).

For the Burbank Rwy 8 ILS, the airplane will fly from the VENTURA initial approach fix (IAF) to join the localizer at 4,400 feet at TOAKS intersection. The 054 degree radial from VENTURA is called a feeder route and comprises the initial approach segment.

• Select NAV-1 to the Rwy 8 ILS I-BUR, 109.5 MHz, inbound 076, and identify.
• To assist in the intercept, select the ADF to VINEE compass locator, 253 kHz, identify UR, and test.
• Continue tracking MC 054 from VENTURA with VOR selected on NAV-2.

Use the ADF to assist the intercept, since the CDI will not start to move until you are within 2.5° of the localizer. The intercept, from MC 054 to localizer MC 076, is only 22°, which is satisfactory. If the intercept was greater, say 60°, it would be a good technique to break the intercept to about 30° just prior to the CDI starting to move. You can judge this using the position and rate of closure of the ADF needle.

If you are approaching the localizer centerline and have not yet been authorized for the approach, query ATC as to whether they want you to either maintain the last assigned heading (possibly for traffic reasons) or to intercept the localizer. In some cases, they will have you fly through the approach course and then turn back inbound. You cannot descend to approach altitude until ATC has cleared you for the approach.

If you are authorized to make the approach, turn to MC 076 as soon as the CDI starts to move. Hold your reference heading, MC 076 plus or minus the estimated wind correction angle, and check the CDI. There is no need for you to center it immediately, just so long as it does not move to full-scale deflection; it is more important to establish a reference heading that stops CDI movement, and then subsequently make gentle turns about the reference heading to center the CDI.

Heading changes of ±5° may be required early in the approach while you are becoming established, but after the final approach fix you should be able to manage with small adjustments of ±2°.

Thorough preparation will reduce your workload during the approach.

Integrate the normal operational requirements into the approach so that the whole thing flows smoothly, without undue haste or panic. Radio calls, prelanding checks, configuration and airspeed changes — the sorts of things that occur on all approaches — still must be attended to. Having prepared for the approach early in order to reduce the workload later on, you should now be able to sit back (more or less) and calmly follow the procedure, attending briefly to other duties as required.

After intercepting the localizer at TOAKS, track to the SILEX Intercept, descending to not below 3,700 feet MSL. While not essential, NAV-2 (if it is available) may be selected to the 316 radial of the LAX VOR, since its intersection with the localizer defines SILEX. You are now in a good position if ATC requests you to hold at SILEX.

Passing SILEX, descend to not below 3,000 feet, indicated on the chart by. The glide slope needle will move from the upper peg as you intercept the glide slope from below. Commence a descent at your estimated rate of descent. There are various techniques recommended for intercepting the glide slope, and your instructor will give you good advice, possibly to:

• lower the landing gear, thereby increasing drag, and pitch slightly down to maintain speed and achieve the desired rate of descent; or
• reduce power, and pitch slightly down.

Again, there is no need to immediately center the needle. It is more important to estab­lish the correct rate of descent and hold the desired airspeed, provided the glide-slope needle does not go to the upper or lower peg. The VSI can be of great assistance.

When settled down in the descent, make minor pitch adjustments to center the glide-slope needle. Airspeed changes, if required, may be made with power (followed by a pitch change, if necessary, to hold the glide slope). Changes in wind speed and/or direction (windshear) will require a response. Windshear is discussed in Chapter 17.

The ILS indicator is a navigation performance instrument — do not use it to make attitude changes, nor to “fly the needles.” Periodically note the position of the localizer and glide-slope needles, then return to the flight instruments and make appropriate minor attitude adjustments on the AI, and steer your selected heading on the HI. Several seconds later, check the ILS indicator, and then move your eyes back to the flight instruments.

Remember that the flight path in clouds or out of clouds is the same, the airplane does not know the difference; the main difference, if any, is in your psychological state — and if you treat the instrument indications merely as substitute visual indications, and keep visualizing your progress down the glide path toward the runway, you can proceed comfortably as in a normal visual approach.

When past SILEX, tune NAV-2 to Van Nuys VOR (VNY), in preparation for a potential missed approach. NAV-1, with the Burbank Rwy 8 ILS selected, is still your primary navigation instrument.

You should pass the outer marker (flashing blue light and “dah-dah-dah-dah-”) at 2,752 feet on the altimeter. Start the stopwatch. The outer marker is the final approach fix (FAF), and you should have the localizer and the glide slope tied down, with only small pitch and heading changes being required. You should be right on speed, with your hand on the throttle. Before landing checks should be complete, with only final flaps to go.

Note. If there is a glide slope failure prior to the outer marker, and you have to revert to a localizer approach, you should cross the outer marker at 3,000 feet, indicated by , and then descend to the MDA 1,140 feet. means a mandatory altitude; you should not be above or below that altitude. You may hold the MDA in the hope of becoming visual before the MAP, whose position you can determine with the stopwatch (at groundspeed 90 knots, 3 minutes 44 seconds after the outer marker).

Assuming the full ILS is working (including the glide slope), proceed down to the decision height (DA/DH) 977 feet MSL, occasionally looking up from the instruments for signs of the runway environment, such as approach lights or the runway itself. If you break out of the clouds at the DA/DH or above, and the required visibility of 1 SM or more exists, you may proceed with the landing. Select final flaps, as required. If the in-flight visibility is below minimums, you may not go below the DA or make a landing. Judging in-flight visibility is your job. The ALS makes a good yardstick since they are of known dimensions; i.e., the ALSF-1 is 3000 feet or half a mile long.

If you do not break out of the clouds at or above the DA/DH, or if the required minimum visibility of 5,000 feet (1 SM) does not exist, then you should immediately commence the missed approach at the DA/DH, by initiating a climb, adopting the missed approach configuration, after passing through 1,500 feet MSL, starting a climbing right turn toward the Van Nuys VOR, climbing to 4,000 feet. Van Nuys is already selected on your NAV-2. If you have only one NAV, turn to an estimated heading, say MH 290, and then select Van Nuys VOR when comfortable. If no “climb to” altitude is published, you should initiate a climb to at least the altitude for circling minimums before making any turns.

The missed approach is not an emergency procedure, but simply part of the normal instrument approach procedure that provides you with a safe flight path if weather is below minimums, or if, for any reason, you decide not to proceed with the landing. The missed approach is, however, a maneuver that you must commence efficiently and without delay when you reach the DA/DH.

International Terminology (DA versus DH)

Jeppesen charts for U.S. airports use international (ICAO) terminology for presenting the minimum altitude on an approach; this differs slightly from the FAA instrument approach chart presentation of minimums.

Precision Approaches (ILS, MLS) with Glide Slope

DA is expressed in feet above MSL; DH is expressed in feet AGL.

Height Above Airport (HAA) typically only published in conjunction with circling minimums and Height Above Touchdown (HAT) are both expressed in feet above ground level.

Jeppesen charts use the term decision altitude (height), abbreviated DA(H), in place of just DH (decision height), as on FAA charts. For example, DA(H) 495' (200') means the decision altitude is at 495 feet MSL, which is 200 feet AGL above touchdown (HAT). Refer to the example in figure 13-49: the FAA Instrument Approach Procedures chart for Visalia, CA, ILS or LOC chart excerpt.

Nonprecision Approaches (VOR, NDB, GPS) no Glide Slope

Jeppesen uses the term minimum descent altitude (height), abbreviated MDA(H). FAA charts use just MDA. For example, the Jeppesen Las Vegas, N Mex, VOR approach Rwy 2 chart shows the minimum as: MDA(H) 7, 540'(675'), where 7,540 feet is the MDA (MSL altitude) and 675 feet is the height above airport (HAA).

Note. United Kingdom, European and Australian ILS approach plates use the international system.

Simultaneous Approaches

At some airports with parallel instrument runways separated by at least 4,300 feet, simultaneous ILS (or MLS) approaches may occur, with different aircraft flying down different parallel paths to different runways. When simultaneous approaches are in progress, you should monitor the tower frequency for radar advisories or instructions.

Note. At some airports with parallel runways with only 2,500 feet between centerlines, so-called parallel ILS approaches may be conducted, but aircraft on the adjacent localizers will be staggered by at least two miles. At some airports with converging runways, ATC may conduct simultaneous converging ILS approaches. The two approach courses will be well separated, the two missed approach points must be at least three miles apart, and the two missed approach courses must be well separated.

The Sidestep Maneuver

The sidestep maneuver is a visual maneuver accomplished by the pilot after flying an instrument approach to one runway, becoming visual, and then sidestepping (with coordinated turns) to land straight-in on a parallel runway which is not more than 1,200 feet to either side of the runway on which the instrument approach is based.

You should commence the sidestep maneuver as soon as you are visual and have the runway environment in sight.

The Localizer-Type Directional Aid (LDA)

The localizer-type directional aid (LDA) is comparable to a localizer but is not aligned with the runway. In other words, using an LDA you will have to maneuver for a landing after becoming visual. The LDA does not have a glide slope as part of the LDA procedure (unless specified in the approach title).

Straight-in LDA minimums may be published if the alignment does not exceed 30° between the LDA course and the runway. Circling minimums only are published where this alignment exceeds 30°.

A good example of efficient ATC use of NAVAIDs is the LDA approach at Van Nuys airport using the localizer part of the Burbank ILS. Since the Van Nuys runway is at almost 90° to the LDA course, only circling minimums are published. If you break out of the clouds at or above the MDA 2,600, and if the required minimum visibility of 1 ¼ SM exists, you may commence a circle-to-land maneuver at Van Nuys (see figure 13-52 on the next page).

The Simplified Directional Facility (SDF)

The SDF is similar to a localizer except:

• its course width may be greater at 6° or 12°, resulting in less precise course guidance (but still good); and
• the SDF course may be offset slightly from the runway centerline, but this will be noted on the SDF approach chart.

The full-scale FLY LEFT or FLY RIGHT signals of the SDF are not usable outside 35° either side of course. Like the LDA, the SDF does not have a glide slope.

Review 13

Instrument Landing System (ILS)

ILS Specifications

1. How far above touchdown is the glide slope of a typical ILS at the middle marker (MM)?

2. If all ILS components are operating and the required visual references are not established, what is the latest point at which you may commence a missed approach?

3. Which range facility associated with the ILS is identified by the first two letters of the localizer identification group?

4. Which range facility associated with the ILS is identified by the last two letters of the localizer identification group?

5. The Pueblo, Colorado ILS RWY 26R has a coded identifier I-TFR. What is this in Morse code (dits and dahs)? What coded identifier (in dits and dahs) would you expect to hear on the outer marker?

6. What indications are received on an ILS as you pass over the outer marker?

7. What indications are received on an ILS as you pass over the middle marker?

8. What indications will you receive on an ILS as you pass over the inner marker, if one is associated with the approach?

Refer to figure 13-53 for questions 9 to 13.

9. At 500 feet HAT, approximately 1.9 NM from the runway, what deviation above or below slope is indicated by a 1 dot deviation of the ILS glide-slope needle?

10. At 100 feet HAT, approximately 1,300 feet horizontally from the runway, what deviation above or below slope is indicated by a 1 dot deviation of the ILS glide-slope needle?

11. At 500 feet HAT, approximately 1.9 NM from the runway, what deviation left or right of the localizer (approximate feet) is indicated by a 1 dot deviation of the ILS localizer needle?

12. At 100 feet HAT, approximately 1,300 feet horizontally from the runway, what deviation left or right of the localizer is indicated by a 1 dot deviation of the ILS localizer needle?

13. At 1.9 NM, the glide-slope needle is 2 dots below its central position, and the localizer needle is 2 dots left of its central position. What is the lateral and vertical deviation from the desired flight path?

14. What does RVR stand for?

15. Having become visual on an ILS approach, what typical landing minimum is required?

HSI and ILS

16. What is the preferable technique when using an HSI to fly a localizer?

17. What will be the result if you accidentally set the reciprocal of the inbound localizer course on the HSI?

Refer to figures 13-54 and 13-55 for questions 18 to 23.

18. Will HSI presentation G cause the HSI to act as a command instrument?

19. Presentation G indicates that the aircraft could be at position:

a. 1.

b. 2.

c. 3.

d. 4.

e. 7.

20. At position 4 with the HSI set correctly, the indication will be presentation:

a. F.

b. G.

c. H.

d. A.

21. At position 6 with the HSI set correctly, the indication will be presentation:

a. F.

b. G.

c. H.

d. A.

22. At position 11 with the HSI set correctly, the indication will be presentation:

a. F.

b. G.

c. H.

d. A.

23. The following HSI presentations correspond to which position(s)?

a. Presentation A.

b. Presentation B.

c. Presentation C.

d. Presentation D.

e. Presentation E.

f. Presentation F.

g. Presentation G.

h. Presentation H.

i. Presentation I.

Unusable ILS Components

24. If two components of an ILS are unusable, the appropriate minimum to use is:

a. the highest minimum required by any single component that is unusable.

b. the same minimum for the fully operational ILS.

c. the normal minimum plus 100 feet.

25. What may be substituted for the ILS outer marker, if unusable? (Six possibilities!)

26. What may be substituted for the ILS middle marker, if unusable?

27. Without glide slope, what does ILS become?

28. What happens to the minimum if the glide slope of an ILS becomes unusable?

29. The minimums for the Durango-La Plata County, Colorado ILS/DME RWY 2 are:

• S ILS-2 6,839-½ 200 (200-½); and
• S-LOC 2 6,980-½ 341 (300-½).

  a. What is the ILS DA (feet MSL)?

  b. How many feet above the touchdown point is this?

  c. What is the minimum if the glide-slope warning flag appears after passing the final approach fix inbound?

  d. What sort of minimum is this?

30. If the glide-slope warning flag appears after becoming visual on an ILS approach, are you permitted to continue the approach to a landing?

Flying the Approach

31. While being radar vectored, if crossing the ILS final approach course becomes imminent and an approach clearance has not been issued, what action should you take?

32. You think you will not be able to lose sufficient height in time to commence an ILS correctly. What two options are available to enable you to lose the excess height?

33. Ideally, drift corrections to maintain the localizer should be so accurately established before reaching the outer marker that completion of the approach inside the outer marker should require what heading change (±°)?

34. What does the rate of descent required to stay on an ILS glide slope depend on?

35. You reduce the indicated airspeed as you descend down an ILS glide path in steady wind conditions. Would you expect to alter the rate of descent to stay on slope? If so, how?

36. You are on slope — glide-slope needle and localizer needle are both centered, but 10 knots too fast. What is your initial correction?

37. You fly into a steadily decreasing headwind. What will happen to your groundspeed? What should happen to the rate of descent in order to stay on the ILS glide slope?

38. If you do not become visual, what is the latest point at which you should commence the missed approach?

Lighting, and Precision Instrument Runway Markings

39. What is the usual glide-slope angle for an on-slope VASI indication?

40. What are the on-slope indications of a two-bar VASI?

41. What are the too-high indications of a two-bar VASI?

42. What are the too-low indications of a two-bar VASI?

43. What are the on-slope indications for a pilot of a small aircraft on a three-bar VASI?

44. What are the slightly too-high indications for a pilot of a small aircraft on a three-bar VASI?

45. What are the grossly too-high indications for a pilot of a small aircraft on a three-bar VASI?

46. What are the too-low indications for a pilot of a small aircraft on a three-bar VASI?

47. How should a pilot of a long-bodied airplane treat the three-bar VASI?

48. What are the on-slope indications for a pilot of a long-bodied aircraft on a three-bar VASI?

49. If you are at a safe altitude with respect to obstacle clearance, e.g., at the MDA, and all bars of a three-bar VASI appear red, what should you do?

50. You have flown an ILS, become visual, and are using the VASI when the glide slope fails. Can you continue under these conditions?

51. The plane of the VASI approach slope only provides guaranteed obstacle clearance within what arc?

52. What color does the tri-color VASI show in the following situations:

a. when the aircraft is above slope?

b. when the aircraft is on slope?

c. when the aircraft is below slope?

53. PAPI lights are white-white-red-red. What does this mean? What is the usual slope?

54. PAPI lights are white-red-red-red. What does this mean? What is your slope likely to be?

55. PAPI lights are red-red-red-red. What does this mean? What is your slope likely to be?

56. PAPI lights are white-white-white-red. What does this mean? What is your slope likely to be?

57. PAPI lights are white-white-white-white. What does this mean? What is your slope likely to be?

58. What does REIL stand for? What is it and what is it used for?

59. On a precision approach runway, what is:

a. the distance from the approach threshold to the touchdown zone marker?

b. the distance from the approach threshold to the fixed distance marker?

c. the distance from the beginning of the touchdown zone marker to the beginning of the fixed distance marker?

60. How is a displaced threshold on an instrument runway indicated?

61. Which of the following is a displaced threshold available for?

a. Taxiing.

b. Takeoff.

c. Landing.

62. Is a displaced threshold at the runway stopping end available for landing rollout?

63. At night, you taxi out onto the end of a runway with the green displaced threshold lights visible ahead. Are you permitted to commence takeoff before you reach these lights?

Simultaneous Approaches

64. When simultaneous approaches are in progress, which frequency should you listen out on for radar advisories?

65. What distance must there be between the centerlines of parallel runways for simultaneous approaches to be permitted?

The Sidestep Maneuver

66. You are cleared for the ILS Runway 7-left approach, sidestep to Runway 7-right. When should you commence the sidestep maneuver?

67. Under what conditions may the sidestep maneuver be performed?

LDA, SDF and ILS Approaches

68. What is the width (°) of an LDA course and a normal localizer course?

69. Is a normal localizer course aligned with the runway?

70. Is an LDA course aligned with the runway?

71. Does the LDA provide glide-slope guidance?

72. Is the SDF more precise than the LDA?

73. What is the width of an SDF course?

74. May the SDF course be aligned with the runway?

75. Does the SDF provide glide-slope guidance?

76. What is a localizer front course with an associated glide slope called?

77. Will a localizer back course have an associated glide slope?