How To Read An Approach Plate

Introduction

The raison d'etre of approach plates is to keep pilots alive. Approach plates are better than the luckiest rabbit's foot you could ever find, because if you know how to read them, and learn the skills to fly the published approaches by the book, then you will be safe. If you lack the patience to read the plates properly, or the ability to fly each course and altitude to the tightest limits, even when weather conditions are against you, then you won't make it as a pilot. Maybe flight simulation is the best way to find that out.

In simulated flight, you can't get killed unless you are really ingenious. In the real world airplanes are softer than mountains, and it is a serious concern of everyone in the business to keep the two apart as much as possible. Approach plates are designed to keep pilots and passengers alive by defining safe descent routes into airports, which can be flown in IFR conditions. Although at the larger airports, incoming flights are very often guided in using radar vectors given by approach control to the pilot, it is essential to be familiar with approach plates because they may well be the only safe way of landing at many airports when VFR is impossible.

For a commercial pilot, the approach plate is merely the last of a series of standard procedures he or she will have to fly - beginning with a Standard Instrument Departure (SID) on take-off, a flight plan involving several different airways, and a transition from the airway structure to the lower levels of controlled airspace. Approach plates, where they are used are the last link in this set of connected routes, but flying an approach correctly requires a high level of concentration.

Approach plates come in a bewildering variety of forms, named according to the primary navaid used in the approach. They also use a form of shorthand which is baffling until you learn enough to unravel its mysteries, but which is extremely comforting when you are flying IFR and have no visual clues to help you get down safely. The early articles in this series will cover how to fly each type of approach, and then, once you have acquired the necessary skills, we will move on to the tougher stuff - dangerous approaches. We will use a variety of aircraft, and each article in the series will come with one or more situations ready to load into Flight Simulator.

Sources for approach plates

Where possible, each article will be accompanied by an approach plate, but as you work through the series, you will in all likelihood want to fly into other airports. In addition to the mainstream sources for real world approach plates, which tend to be expensive, there are several sources of approach plates for flight simulation:

Jeppesen SimCharts - payware CDs which cover all airports in the US, and airports with runways longer than 6000 feet elsewhere in the world. SIDs, STARs, transitions and airport diagrams are included for many airports. The US and European CDs are available with en-route charts included as an option. SimCharts are real-world approach charts, but they are only for simulation flying. [Available here.]

Final Approach - an excellent product available from Flight Sim Central as payware or the Final Approach web page as shareware. Final Approach has been designed specifically for flight simulation and not only allows you to view approach charts, but to design them. About 4500 plates are available, which makes Final Approach very good value for money. Georges Lorsche, whose brain-child Final Approach is, has kindly given us permission to use plates for this series.

The FSS Project - payware charts in PDF format for flightsim use. From time to time freeware charts are available on the website.

UK Approach Charts can be viewed and dowloaded freely from the National Air Traffic Services website under this URL.

Clearance Unlimited - a free service with plates available

Echo Flight - digital scans of NOAA plates for the lower 48 states

Digital Aeronautical Flight Information - a good source of plates in pdf format

You might also like to visit the Dangerous Airports Database run by Philip Sauerteig

If you are aware on any other sources, please let me know and we will add them to the list.

Entry to the approach structure

One of the great mysteries to many people is how pilots know how to get to the place where an approach procedure begins. The answer, as it happens, isn't as difficult as it might seem. The one time you are virtually never going to require an approach plate is for VFR conditions in a light plane - in that case you would descend and fly the traffic pattern until the aircraft was aligned with the approach course. Another time you won't need an approach plate is when ATC are vectoring you onto the ILS; in this case they will steer you around the obstructions at altitudes that are at or above the Minimum Vectoring Altitude (MVA). The whole point of an ILS is that you can just fly needle right down to the decision height and land if you meet the requirements for further descent.

With few exceptions, the way you "get onto" an approach plate is by an ATC-authorised descent from the en-route structure; in other words from the airways. Descents can be radar controlled, or they can be done via Standard Terminal Arrival Routes (STARs), which are approved methods of leaving an airway and flying towards an airport. If you are not being vectored by ATC to a final approach course, then you must make your approach using an authorised procedure, and this is where approach plates come in. An aircraft exiting the en-route structure without vectoring should carry out the entire procedure given on the plate starting at an Initial Approach Fix or an authorised feeder route, unless the IFR clearance is cancelled and it is possible to go visual. Actually, there is one case where you may get clearance to fly an approach procedure without having exited an airway and that is if you are unlucky enough to have to request a "pop-up" IFR approach, having got caught out in VFR conditions which have gone bad on you.

The anatomy of an approach plate

There are so many different types of approach plate that it is hard to give more than a general overview of approach plate layout, but in the interests of avoiding confusion, some general conventions are followed. If one of your pet favourites isn't here, forgive me, I gave up trying to win them all some years ago.

The Header

This identifies which airport the plate relates to, and identifies the type of approach. It also gives specific data on frequencies, and a revision date for the document. On many plates there is also a circle which displays Minimum Safe Altitude information - the MSA circle is found at the bottom right of a Final Approach plate. The only time the MSA is used is in VFR flight, or during an emergency - one time you might need it is in order to line up for a VFR approach at night, another is when conditions suddenly become IFR.

Pay close attention to the title - in red on this example from Final Approach. The format of [Primary navaid type/DME] [Runway/Letter] is always followed. If an approach description is in the Navaid/Runway format (e.g. NDB Rwy 34) this indicates that the final approach course is lined up within 30 degrees of the runway and that the descent angle is acceptable; in other words, reasonably close to 300 feet per nautical mile. This type of approach is called a "straight-in" approach and will have straight-in minima listed on the plate. If the approach description gives a letter instead of a runway (e.g. NDB-A) then this means that the approach is to the airport rather than a specific runway, and it will list "circle-to-land" minima instead. An approach description in this format should always ring alarm bells, because either the final approach segment is at an angle of more than 30 degrees to the runway; or the final approach gradient is greater than 400 feet per mile.

The types of approach are usually classified by the primary navaid which is relied on, thus you will see NDB, VOR, TACAN, ASR, LOC, ILS, PAR, LDA, SDF and GPS approaches - as well as charted Visual approaches, which rely on nothing more sophisticated than your eyeballs; and Helicopter approaches, which require a helicopter. Each type of approach may be qualified in turn as requiring DME equipment (for example VOR DME Rwy 34) and a chart may show several different types of approach on the same page (for example VOR or GPS Rwy 34).

To execute a charted instrument approach, you must have adequate navigational aids to fly the procedure - for example, you cannot fly a VOR approach if you only have an ADF fitted, and you cannot fly a VOR DME approach unless the aircraft is equipped with both a VOR indicator and DME equipment. But don't forget that you will very likely need additional equipment in order to transition to the approach procedure from the enroute structure. If you have to transition from a VOR, you aren't going to be able to fly it if the aircraft only has an ADF fitted. While we are on the subject of equipment, the other trap is that very occasionally equipment needed to identify the missed approach point (MAP) and holding fix is not listed on the approach chart, so check the plate very carefully for this before you execute the approach. It is no time to find you need an ADF or DME gear when you are descending in 8/8 cloud.

The MSA circle repays close attention, because it defines the minimum safe altitude within 25 miles of a navaid located on or near the airport. Sometimes there is a single central figure in the MSA circle, but more often than not it is subdivided into two or more sections with a different altitude in each one. The lines which subdivide the sectors are marked with courses towards the navaid, which makes it easy for a pilot to identify which sector he or she is in. The MSA gives you 1000 feet of obstruction clearance and it is usually given in feet (e.g 7500'), although on some charts the figure may appear as a bold numeral with a subscript next to it - the bold numeral is the altitude in thousands and the subscript is the altitude in hundreds. The MSA is not Holy Writ - you can descend below it, but when you are below MSA you should have a high level of awareness of terrain - and unless you are executing an approach procedure or are being vectored you should not begin descending below it in IFR conditions.

Other data which may appear in the header includes airport elevation (pay very close attention to this), threshold elevation, transition altitude and magnetic variation.

Approach plan view

Below the header is the approach plan view. This shows an approximately north-up view of the approach as seen from directly above, and it is not to scale. It allows you to identify the Initial Approach Fix (IAF), which is the point from which the approach procedure begins, the courses you need to fly in order to complete the approach, and any procedure turns (a standard method of reversing an aircraft's course) that are needed. The IAF should be clearly labelled on the chart, and depending on the chart, there may be several IAFs, one for every possible initial approach segment.

The plan view also allows you to identify the frequencies of navaids and the ILS, if there is one. High ground is usually identified, as are obstructions like beacons. You should also be able to identify the general outline of the missed approach procedure (shown as a broken line on most plates) and any holding pattern associated with it (shown as an elongated oval, blue on Final Approach plates).

Using the plan view, the approach can be divided into an initial approach segment, intermediate approach segment, final approach segment and a missed approach segment.

Initial Approach Segment:

The initial approach segment begins at the IAF and ends where it joins the intermediate approach segment. The reason for flying this section is to get aligned with the final approach course, and a variety of standard methods of doing this are used, including procedure turns, DME arcs, and if all else fails and no-one can think of a more difficult way of doing it, a common-or-garden track leading straight in to the intermediate segment.

Just to confuse things, it is not uncommon for charts to show several different initial approach segments leading to different IAFs - for example, a VOR approach plan view might also show one or more DME arc initial approach segments, each with their own IAF.

When plan views get cluttered, the designers follow conventions which make them easier to read. You would expect to find any route capable of taking an aircraft to an IAF joined to the fix by a line (a thick line on Jepp charts) - but this is not the case. Every now and then a chart will show a navaid which can be used to navigate to the IAF, but without a line joining the two. In this case there will be some text under the navaid identifier which will give a course, altitude and distance to a clearly identified IAF. This usually happens on cluttered plan views and is done to reduce confusion, but it is surprising how easy it is to miss the text.

The intermediate segment

This begins at the intermediate fix (IF) and finishes at the beginning of the final approach segment. The course for this segment is normally aligned within 30 degrees of the final approach course, but in some cases may not be, usually due to terrain considerations. The purpose of this part of the approach is to prepare the aircraft for final descent, and while you are executing it you should be completing the checklists, reducing airspeed and making one last check of the approach procedure. Approach charts don't always identify the IF, in which case the intermediate segment begins when you are inbound to the final approach fix (FAF), and correctly aligned after completing any procedure turns.

The final approach segment

Allows you to fly to a point from which you can complete a visual landing. There are two types of final approach segment:

1. a non-precision approach: which begins either at a charted FAF (a propellor-like cross on most plates), or, when an FAF isn't shown, at the point where the procedure turn is completed and the aircraft is established on a final approach course inbound to the runway. In the latter case, the point where the final approach segment begins is known as the Final Approach Point or FAP. A non-precision approach gets its name because no glideslope information is available.

2. a precision approach: which begins when the ILS glideslope is intercepted at the minimum glideslope interception altitude.

The missed approach segment gives you an opportunity to get out alive if you can't satisfy the landing minimums. The missed approach point (MAP) varies depending on whether you are flying a precision approach or not:

a. for non-precision approaches is very clearly identified on all approach plates with a large letter M which is smack on top of your descent path - do not confuse this with the Middle Marker, which if present will be labelled MM. In flight the MAP can either be identified as the moment you arrive at prescribed height over a navaid, or when a defined amount of time has elapsed after leaving the FAF.

b. for a precision approach on an ILS, the MAP is reached when you are at a defined altitude on the ILS known as the Decision Height (DH). The DH is clearly stated on the plate.

Profile view

The profile view is at least as important as the plan view. Here you will glean everything you need to know about the altitudes required to fly the approach procedure and the distances you will cover on each leg. You begin your reading from the IAF: the majority of procedures will require you to lose altitude on an outbound track, fly a procedure turn, and then begin an inbound descent, but this is not universal; ILS approaches such as the one shown in here, usually lack an outbound track. Pay close attention to the altitude given at the IAF - here it is 3000 feet. Depending on the type of chart you are using, there may be lines above or below the number. On NOS and Final Approach charts a line below the altitude shows that it is a minimum altitude, a line above the number indicates a maximum altitude, and a line above and below indicates a mandatory altitude - you must cross at exactly that level. Jeppesen charts do not use lines, but will state "mandatory" or "maximum". In general, all altitudes without lines can be assumed to be minimum altitudes, whoever publishes the chart.

The profile also shows other information such as stepdown fixes, which are put there to control descent over obstacles, or to fit with local traffic patterns, touchdown zone elevation (TDZE), which is the highest point in the first 3000 feet of the runway; airport elevation, which is the highest point of usable runway anywhere on the airport; and threshold crossing height (TCH), which is the distance between your wheels and mother earth when you cross the threshold on the centerline of the glideslope. All altitudes on the profile usually have a Height Above Touchdown (HAT) in parentheses after them - this is the difference between your altimeter reading and either the TDZE or the airport elevation if a TDZE is not stated.

Speeds, distances and descent rates

When you look at distances given on approach plate it is vital to work out where they are measured from. A quick check of the profile view is usually the best way to do this. For precision approaches, distances given along the "ground line" of the profile view are normally measured from the ILS DME equipment - which is generally on the threshold, and the chart header will give the frequency for the ILS. For non-precision approaches, distances are likely to be measured from a navaid somewhere near, but not necessarily on, the airport. One way of working out where distances are measured from is to look for a zero on the profile; this will normally be on the threshold or under a navaid. Occasionally, when it wouldn't otherwise be clear where the "origin" is, distances will be explicitly stated in the form "D2.4 SMO" or something similar. When no clue is given, like the profile above, some deduction may be required - in this case the distance is calculated from the ILIP ILS.

Why should you bother to take so much trouble over establishing from where distances are calculated? Well, on a non-precision approach, the only way of calculating distance might be on the basis of the timer and a calculation of your groundspeed, and if you complete a procedure turn too far from the threshold on some approaches, you could hit a mountain. On a precision approach, if your NAV radio is tuned to the wrong navaid, then your DME will be wrong and your MAP will be way off, possibly with fatal consequences. So there is a certain amount of self-interest involved in getting this right.

How fast should you descend? When you have to make a descent as part of an approach (and let's face it, few approaches require you to go up), you should assume that the plate has been drawn for rates of less than 800 feet per minute. 700 is probably a good figure to aim at if your IAS is more than a hundred knots. If an approach seems to require a faster descent rate than this - check it. Either it will have a letter instead of a runway after the navaid (e.g. NDB-A, rather than NDB Rwy 34) or you have made a mistake.

Speeds on approach plates are usually given as groundspeeds. Pay attention to this. If you have to calculate how long it is going to take an aircraft to go from A to B on a plan view, remember that Indicated Airspeed (IAS) is going to be less than your groundspeed unless you are at sea-level (though to all intents and purposes the difference is not worth worrying about below 3000 feet. One other thing worth remembering is that if ATC isn't telling you otherwise, the maximum speed authorised for a procedure turn is 200 knots IAS. While this won't be a problem in a Cessna 182, it may be material in a big jet.

Landing minimums

These show the minimum requirements for altitude and visibility necessary to execute the final approach, usually divided into two columns: "straight-in" landing requirements; and those for a "circle-to-land" approach (which in short-hand plain English, means doing a circuit).

The most important figure here is the MDA/DH, which will vary according to the speed of the aircraft you are flying, and whether you are undertaking a precision or non-precision approach. Be aware that there is a great deal of variation between different publisher's charts here. Jeppesen lists what is called a "Decision Alititude (Height)" or DA(H) which is given as an Mean Sea Level (MSL) altitude - i.e. the altitude your altimeter shows - followed by a Height Above Touchdown (HAT) in parentheses afterward. ICAO and Final Approach show Decision Altitude in MSL, followed by Decision Height, which is the height above TDZE. NOS use basically the same system as Jeppesen, but a slightly different presentation.

The importance of the MDA or DH is that these are never-go-below altitudes unless you can see the runway. There is one caveat - you also have to observe any visibility requirements stated in the minimums. Visibility is either stated by the tower in statute miles and fractions of miles, or determined by what is known as Runway Visual Range equipment (RVR) and given in hundreds of feet.

The minimums can be very complex, with different columns for each type of approach, and variations to allow for equipment downtime. If you inspect a plate like the one above you will see a grid with the letters A, B, C and D in it, with maximum speeds next to each. The letters refer to what are known as "approach categories" and they are calculated by multiplying the stall speed of the aircraft in a landing configuration by 1.3. Most light aircraft are in category A, piston twins tend to be in category B, turboprops in C or D and so on.

In an extreme case, there may be four columns for different types of approach, each of which has different visibility requirements according to category of aircraft, but fortunately this is rare. It is quite usual for visibility minimums to be grouped across all four categories, resulting in one figure. Taking one example at random, the SimChart for Montreal ILS Rwy 06L groups all the categories under one vis requirement of "RVR 26 or 1/2" which translates to 2600 feet RVR or one half mile visibility according to tower, and this applies whether you are flying a 172 or a 747.

The final part of the minimums is the circle-to-land box. Again you will see the A,B,C,D categories, but against each there will be an MDA(H) or similar, and a visibility requirement, usually expressed in miles. Unless the visibility requirement is met for your category of aircraft and the runway is in sight, you may not descend below the MDA, and you can only circle-to-land if the aircraft is configured for landing. For each category of aircraft there is a circle-to-land radius which is not defined on the plates; this never-exceed distance is measured from the ends of the runways, and it is in force even if the actual visibility is greater. For information, the radii are: A=1.3 nm; B=1.5 nm; C=1.7 nm; D=2.3 nm; and E=4.5 nm.

Other data

The last pieces of information on the approach plate are the no-circling chart and the time and distance to the MAP from the FAF. A no-circling chart is sometimes present if there are obstructions near to the airport and it clearly defines no-go areas. In any case, you should read the airport diagram in conjunction with the approach plate as there is more valuable information here. The time to MAP is given in a table down at the very bottom of the chart, and it is especially useful if the MAP is not identified with a navaid. If the MAP can only be identified by a DME measurement, then you need to cross reference your groundspeed with the chart, memorise the number and start the timer at the FAF. When the time is up, you are at the MAP and if you aren't visual at that point, you need to execute the missed approach procedure

Missed approach procedure

This is is shown diagramatically in the plan and profile view, and on most charts it is also explained in text elsewhere on the chart. This procedure should be memorised, because things can happen very quickly once you reach the MAP and it is no time to be wondering what to do next.

Conclusion

By now everything is probably as clear as mud; there is a great deal of information to take in, isn't there? So because you can't possibly absorb it all in one reading, I have worked up some tutorials for you to fly. Each of these tutorials teaches something new about approach plates, and they should be your next stop. Georges Lorsche has very kindly worked up an approach plate for each tutorial, but otherwise they can all be found in Final Approach or on the SimCharts Canada/Alaska CD.

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