Procedural Instrument Approaches Explained

Procedural Instrument Approaches explained

This can only be considered a brief description on IAP's. Trevor Thom needs a whole book on the subject and it is impossible to compress all the information into one web page.

What's a Procedural Approach?

Many pilots flying online with VATSIM or IVAO may not become familiar with procedural approaches. As both are online ATC systems the usual procedure is for an aircraft to contact Approach Control and be radar vectored onto the ILS.

In real life not all airfields have radar and, for those that do, radar can be taken out of service or fail. In these cases a pilot will not receive a radar service but will have to fly the procedural

approach for the airfield. A procedural approach is therefore a pilot based procedure by which he can position onto final for any runway that has a published IAP.

Types of Approach

Approach plates can be found for ILS approaches (known as a Precision Approaches) but can also exist for NDB's or VOR's. These are Non Precision Approaches as they do not have any vertical guidance and, obviously, the minima for these approaches are higher.

Before you start

There are some basic rules to follow before you start flying IAP's.

a. Be fully familiar with the aircraft you are flying. IAP's require a lot of concentration so make sure you can fly the aircraft without any need to search for gauges or switches. Also make sure you know the performance of the aircraft - especially holding and approach speeds and that the Nav displays are easy to read - you may often be flying data from NAV2 or the ADF as well as the primary NAV1 display.

b. Learn how to read and understand IAP's. You may not always have the luxury of time to digest an IAP so the data needs quick assimilation. IAP's introduce holds, Step Down Fixes, Decision Height, Missed Approach Height and Missed Approach Point (amongst others) into your terminology - make sure you know what they are.

c. Preparation is everything. The more you can learn during the planning stage the better - it is always easier to understand something on the ground prior to flight than after you get airborne.

Learning the Chart

The printed charts have a lot of information on them so a lot of it has to be condensed. Much of this will be by symbols or syntax you may be unfamiliar with but it has to be learned. The codes and symbols used may be slightly different with the various publishers (AERAD, Jeppesen, CAA) so you should use the same source legend. I've not seen a CAA legend so they are a bit unhelpful in this.

Charts are split into several sections as you can see from the picture above. The top section has general airfield data. Make sure you check the procedure name is the one you want (don't use the LOC/DME in mistake for an ILS/DME) and make note of the airfield altitude and the Minimum Sector Altitudes.

The main diagram shows the plan view of the IAP. It may contain several variations of the procedure so check closely to see the one you need. The prime procedure is a solid line with alternative procedures as dotted lines. In real life the alternative procedures may be used far more frequently as they are designed for airways traffic.

The plan view shows the routes to be flown, the navaids and frequencies and the holding patterns. Ronaldsway is a good place to learn as it has VOR holds, NDB holds, holds at fixes, a DME arc approach and NDB intercept approach and an NDB (Locator) outbound approach - a veritable mix for a small airfield. That is just for the ILS too - it also has VOR and NDB approaches!

Below the plan graph there is a descent profile table. This is a DME/height cross check you can refer to if you suspect incorrect glidepath readings or the glidepath fails.

The next section is a vertical diagram and as well as displaying the vertical profile it shows the Missed Approach Procedure and the FAF (Final Approach Fix).

The final section has tables for Obstacle Clearance Heights, Visual Manoeuvring Heights, Rate of Descent for varying airspeeds, notes and warnings. This section should never be ignored as there may be snippets of information here that are extremely valuable.

Skills Required

As mentioned above it is assumed you have a full knowledge of the performance of the aircraft you are flying and know the operation and use of the navigation kit. You also need to know your aircraft's category as Cat A, B, C or D approaches may all vary. The Category is based on threshold speed and for this you need to refer to the appropriate tables.

Your flying skills will require the ability to do the following:

1. You should be able to track directly to a VOR, NDB or intersection. 2. You should be able to track from one intersection to another. 3. You should be able to track into or outbound from a VOR or NDB on a specific heading. 4. You should know how to teardrop over a position to achieve the above. 5. You should be able to fly DME arcs. 6. You should be able to fly holding patterns. 7. You should be able to do all the above correcting for any wind. 8. You should be able to fly a correct descent profile for non precision approaches using the

correct rate of descent for a given airspeed. 9. You should be able to fly Step Down Fixes.

The above sounds a lot but training should involve learning these stage by stage until you are familiar with all possible techniques.

Reference Material

There are many sources for information on flying these instrument procedures. Early versions of FS had some very good tutorials in the included books and later versions have similar help pages. As these are real world procedures you can also look out for second hand copies of books like Trevor Thom's "Instrument Flying".

You should also take time to read the CAA AIP pages on this subject. This material is buried away a little but you should find it in the AIP section under Aerodrome Data - Generic, AD 1.1.1, Aerodrome/Heliport Availability, General Conditions. You can skip the first five pages if you want although there are some interesting nuggets to be found but the really important bit is on AD 1.1.6 on Aerodrome Operating Minima.

Moving on

In the next page I will look at one specific ILS procedure for EGNS and describe the flight profile in more detail. Click on the Next button below to continue.

Before we start

Before we look at a specific procedure - in this case the ILS/DME approach to runway 26 - a word of advice regarding ATC.

Despite rumours to the contrary ATC are not mind readers. If you are inbound to an airfield then ATC will normally radar vector you to the ILS for the runway in use. If you want to fly a procedure you need to tell them. For a start I would advise that you put in the remarks column of the flight plan: RMK/INSTRUMENT TRAINING

Secondly, on initial contact with approach control, you should inform them of the training you would like to carry out. You should say that you wish to fly the procedural ILS approach for 26 and specify the point at which you wish to commence this procedure - as I will show below there are five possible holds from which the procedure can begin.

Telling ATC that you wish to fly a procedure informs them that you want to fly the approach yourself and do not require radar vectoring. ATC will try to accommodate this but a procedural training approach is always subject to other traffic - ATC may decline the request, offer an alternative or suggest delaying until traffic has eased off (a delay usually meaning going into a holding pattern). ATC may also accept your request but give you initial radar vectoring to provide separation for other aircraft - but will put you back on your own navigation as soon as possible.

Flying the ILS

The ILS plates for most airfields are quite basic and there may be only one procedure to fly. The ILS at Ronaldsway has five procedures from five different stacks and all are different. They are:

1. A DME arc procedure from KELLY. 2. An NDB intercept from VANIN. 3. The direct procedure from overhead the RWY NDB. 4. A procedure from the IOM VOR. 5. An offset NDB intercept from CAR NDB.

Different skills are required for all these approaches and most requires the ILS setting up on NAV1 whilst flying the aircraft from the VOR on NAV2 or tracking an NDB on the ADF. Good cockpit discipline is necessary for any procedural approach.

From the time you leave a holding pattern you should pay particular attention to speed. Procedures are based on rate 1 turns and if flown at excessive speeds you will never achieve the designed paths. Aircraft should never fly a holding pattern above 210kts and it follows that all procedures require the aircraft to be at this speed or less.

Below I will describe each of the five procedures.

From VANIN

This is the easiest of the five approaches. Aircraft inbound to EGNS on W2D from POL VOR are normally cleared to VANIN at FL45 or FL50. As you can see from the plate above, having been cleared for the procedural approach you would:

1. Track from VANIN to CAR NDB. A no wind heading would be 305 (shown on the chart as QDM305). After leaving VANIN you would also descend to 2000ft QNH (1967ft QFE).

2. As you reach IOM radial 088 (or RWY QDM268) you should start seeing the Localiser needle become active and a turn should be made to capture the ILS.

3. 2000ft should be maintained until 6 DME (the FAF). If the approach is stable you then descend on the glidepath but if the approach is not stabilised at FAF it should be discontinued.

Although a simple approach there are several points you should be made aware of. First is that on leaving VANIN you tune NAV1 to the ILS. ADF should be tuned to CAR and it is this instrument that becomes your prime navigational source as you track to the NDB. As you leave VANIN you also start descending to 2000ft and so aircraft management (especially speed) should be under complete control. You should never intercept an ILS higher than 160-180kts.

In FS you don't have two ADF's so it is impossible to tune to RWY NDB to get the 268QDM marker to signal the ILS activating. The only option here is to tune NAV2 to IOM VOR and use the 088 radial as the guide. I need not add that you are now using all three nav sources for data - tracking directly from the ADF whilst watching the NAV2 needle to centre which should indicate the ILS becoming active.

Once you establish on the ILS the rest of the procedure is as you have flown many times before.

From IOM VOR

Aircraft from Dublin (on W911D), Glasgow (on W928D) or Belfast (on L10) will normally be cleared to the IOM VOR at 3000ft.

1. On reaching the VOR you fly directly to the RWY NDB. 2. Leave the RWY NDB on a track of 094 (for Cat A and B aircraft) or 100 (Cat C and D)

aircraft. You should know your category after checking the CAA pages. 3. As you leave the RWY NDB you also descend to 2000ft QNH. 4. At 8 DME IRY you start a Rate 1 turn to the left to intercept the ILS.

Again there are cautionary comments to make. Before reaching the IOM VOR you should have RWY NDB tuned on the ADF ready to turn direct to the NDB. You should also retune NAV1 to the ILS as soon as you leave the VOR. Having run out to 8 DME on the outbound leg of the procedure, unless you have corrected for wind, your turn onto the ILS may undershoot or overshoot the centreline - be prepared for this. If you have forgotten to retune NAV1 to the ILS it will mean that when you start your turn at 8 DME you are still reading this from the IOM VOR and will only be 3.5nm from the airfield - the approach will then go horribly wrong!

From RWY NDB

This is almost identical to the IOM procedure above except you will be going directly out on the procedure. The only caution with this approach is that if you are flying direct to the NDB before starting the approach you may need to fly an intermediate teardrop pattern to ensure you establish on the correct outbound heading. I will describe teardrops later.

From KELLY

Aircraft from Manchester, London and the SE on L10 will normally be cleared to KELLY at FL80.

1. Leave KELLY on track to the IOM VOR and begin descent to 2000ft QNH. 2. At 13 DME IOM turn right to fly the 8 DME arc from IRY DME. 3. As you reach IOM radial 091 start a left turn to intercept the ILS.

Lots of traps for this approach. The first is when you are past KELLY and flying towards the IOM. At DME 13 you begin a turn to the right to pick up the 8 DME arc from IRY and with the VOR on NAV1 this means the ILS will be on NAV2. Plan ahead here and before you get to KELLY tune NAV2 to the VOR, switch to HDG mode and then tune NAV1 to the ILS. Watch for 13 DME on NAV2 and then, once you start the turn, all your flying is now on NAV1 whilst you fly the arc and capture the ILS. You are not finished with NAV2 though - reset the OBS to 091 and watch for the needle to centre whilst flying the arc as this is the mark for your turn onto the ILS.

For most of this procedure you are descending and turning at the same time - this is not normal for the other procedures above and may feel odd.

From CAR NDB

Left to last as this procedure can only be flown from the CAR holding pattern. CAR is no longer part of any airway and so this procedure is only used for training purposes. The chart shows the LHA (Lowest Holding Altitude) as 2600ft but it is more normal to fly the hold at 3000ft. Read the chart carefully and compare with the instructions below.

1. As you pass overhead CAR on 291 you begin a right turn onto 111. Start the stopwatch as you pass over the NDB.

2. After 1 minute (Rate 1 turn) you should be on heading 111 and abeam the NDB. 3. After a further 30 seconds (total 1:30 on stopwatch) start a descent to 2000ft. 4. After another 1min 30 sec (total 3:00 on stopwatch) turn right to intercept the ILS.

Timing is everything with NDB holds so a stopwatch is a very useful item. You cannot fly this procedure without one, even in FS.

Training Routes

All the above can be flown individually but a variety of techniques can be practised with a good training route. The chart below shows a typical base check route for the Isle of Man. The route is as follows.

After departure fly to KELLY, reverse course and route KELLY - IOM. At IOM turn to CAR NDB and enter the hold. Fly the hold twice and then fly the alternate procedure for the ILS.

Although it looks simple on paper the route tests several disciplines. It requires both NDB and VOR tracking, flying over a position and reversing course on a specific radial, flying an NDB holding pattern and, finally, completing a procedural ILS.

At the end of this exercise the aircraft would go around at minima and climb out for a second ILS approach or a VOR/DME approach onto Rwy 08.

We haven't discussed teardrops yet so I will continue with these.

Starting the Procedure

For many procedures the starting point of the IAP is a holding pattern. This makes sense as the stack is the point at which aircraft may be placed in a queue for the approach. It is also important to note that once in the stack the aircraft are flying the correct headings to begin the procedure - the inbound heading of the hold allowing continuation directly into the IAP.

Not all aircraft will hold before making an approach. If there are no aircraft ahead the aircraft will be cleared directly into the procedure - but it could be approaching the fix from a direction which makes it impossible to establish on the correct inbound heading.

Let us look at the ILS approach from IOM VOR as an example. In the diagram below only the IOM procedure is shown for clarity.

You already know the procedure from the IOM - tracking 082 to RWY at 3000ft to start the outbound leg on 100 (if Cat C or D). Aircraft in the hold can do this easily because they are already running inbound to the VOR on this heading. Aircraft which are not in the hold could be approaching the IOM from very different directions - and this can make it impossible to start the procedure directly.

You can see from the above chart that aircraft can approach the IOM from four airways. Whilst aircraft from BEL or DUB could start the IAP directly (as the turn over the IOM towards RWY is not excessive) this is not possible for aircraft from BLACA (on W928D) or from DCS (on W911D) as the turn would be to great - see below.

For the aircraft on W928D any turn towards the RWY would take it well south of the track to RWY and the aircraft would be in an impossible position to fly the rest of the procedure. The same would apply to aircraft from DCS flying the route marked by the green arrow.

The correct entry into the procedure is to ensure you are established on a sympathetic heading towards the VOR before tracking to the RWY. This involves flying a pattern known as a teardrop.

Teardrop Procedure

The teardrop is a pattern the pilot has to calculate - it isn't written in the books. It's purpose is to put the aircraft on an inbound heading to the point at which the procedure starts - in this case towards the IOM VOR on a heading of 082. This is what it would look like.

The basic teardrop involves flying away from the facility at 30 degrees off the outbound heading for two minutes - and then a rate 1 turn to the right back to the beacon.

In the example above the aircraft needs to fly outbound on 232. Should the aircraft have been approaching from the south (say from KELLY) then an outbound heading of 292 would be the correct heading with a left turn back to the beacon.

This procedure isn't meant to be precise (but more skilled pilots can make it so) but it will bring you back to the beacon on a heading that makes the rest of the IAP less traumatic.

Further examples

Let us look back at the I/R Route from the previous page.

You may now see that two teardrops are needed here. The first is when the aircraft reaches KELLY and has to almost reverse course to fly the 308 radial to the IOM. In this case 308-180(reciprocal) = 128 + 30 (offset) = 158. So here you would fly 158 for two minutes and turn left back to KELLY, hopefully on 308 ready for the track towards the IOM.

Again at IOM a teardrop would help establish on the track towards CAR NDB. Here the track isn't published on the IAP and so your would have to work out the headings from your flight log. Roughly from memory you would fly out on 285 to turn left and track in on 075.

A teardrop is a very useful procedure and you can use it at any navaid or fix to leave that point on a specific heading. To some extent it has been replaced by GPS and FMS but it is a skill that is well worth learning.

Holding Patterns Everyone hates these but they aren't so difficult if you have learned the above skills.

For many FS pilots a hold is something unpleasant, maybe unknown and probably a bit daunting. It need not be.

A hold is simply a means of delaying aircraft in an orderly fashion. Usually they are stacked in the hold at 1000ft intervals with the aircraft at the bottom of the stack being the next to start the procedure when this is possible.

There are two processes to learn for the hold. One is the holding procedure itself and the other is the means of getting into it in the first place - the hold entry procedure.

The Hold

Holding patterns are time based procedures so a stopwatch or clock with a second hand is very, very useful to have.

The normal hold is a 4 minute procedure describing a racetrack pattern. In the case of the hold shown above it starts with the aircraft passing over the holding facility (IOM VOR) and turning right onto 262. This is a Rate 1 turn and will take 1 minute. When steady on 262 the outbound leg is also flown for 1 minute and then a right turn is made back onto 262. Again this is Rate 1 taking another minute and the aircraft will then fly 262 back to the VOR completing a four minute pattern.

Some holds are 6 minutes and in these cases the outbound leg and inbound leg are extended to 2 minutes. Some holds are left hand patterns and some are right hand.

Essentially that is it - but nothing is easy in flying. The headaches start to appear when there is some wind about - and learning how to correct for this. To be honest I won't describe this here as there are better online tutorials that cover correction calculations - but I'll illustrate why a pilot should be aware of the effects of wind.

Above you see what happens with a westerly wind. As the aircraft starts to turn outbound it drifts east, the outbound leg is shorter than normal (flying into a headwind) and the inbound turn can finish with the aircraft very close to the VOR. This will end up as a 3:30 pattern or less.

If the wind is across the pattern the effect is more difficult to correct. With a southerly wind the initial outbound turn is shortened because of turning into a headwind. The outbound leg see the aircraft drifting further north and the inbound turn is extended as the aircraft now has a tailwind. The result is that the aircraft can end up substantially north of the inbound track of 082.

The solution here is to assess drift angle when inbound to the facility. As you can't correct for drift in the turn the outbound leg is flown at 3 x drift angle - resulting in a pear shaped pattern rather than the more normally expected racetrack. For those of you who have read this far the drift angle can also be calculated by using windspeed / TAS x 60, so for a 25kt crosswind and a TAS of 150kts the drift angle is 10 degrees. In the above pattern the inbound leg would be flown on 092 and the outbound leg on 232.

Hold Entry Procedures

I say procedures because there are three of them. All are based on the teardrop pattern described earlier and there are three because it depends on the direction you approach the hold - this being the same headache as the direct entry to a procedure.

Before describing each procedure I must take time to explain the hold entry chart.

Take a few minutes to familiarise yourself with the diagram. Note the inbound track to the hold and the holding pattern direction. This is a typical hold entry diagram so it requires a little agility to relate it to a specific hold you may be intending to fly - it can be awkward mentally rotating it to the correct inbound heading.

The diagram shows the three sectors for the different entry procedures. I have colour coded these for clarity. As the IOM hold is from the opposite direction the example above the image requires rotating 180 degrees to make sense. So let's do this to make the first example easier to visualise.

The inbound heading for the hold is 082 so we can work out the headings for the three sectors.

Aircraft flying to the VOR on a heading between 012 and 192 fly a Sector 3 entry.

Aircraft flying to the VOR on a heading between 192 and 262 fly a Sector 2 entry.

Aircraft flying to the VOR on a heading between 262 and 012 fly a Sector 1 entry.

The above may sound complex but it's harder to explain on page than it actually is. Look back at the IAP and you will find that the entry procedures are easy to visualise in most cases. Using the above diagram it is not hard to see that aircraft from Dublin (W911D), Glasgow (W928D) and Belfast (L10) would fly Sector 3 entries, aircraft from Liverpool and the SE (L10 AND W2D) would fly Sector 1 entries and aircraft from Carlisle or Newcastle (W911D) would fly a Sector 2 entry.

Now we need to know the actual entry procedures.

Sector 1 - Parallel Entry

With a Sector 1 procedure the aircraft crosses the facility and flies the reciprocal of the inbound heading for 1 minute (or 1.5 minutes if a 6 min hold). A Rate 1 turn is then made back to the facility and the hold is started.

Sector 2 - Reverse Entry

With a Sector 2 procedure the aircraft flies a teardrop as we have used earlier - flying an offset of 30 degrees fom the reciprocal heading for the hold. After 1 min (or 1.5 min) a Rate 1 turn is made back onto the inbound heading of the hold back to the facility.

Sector 3 - Direct Entry

With a Sector 3 procedure the aircraft enters the holding pattern directly.

Non of the entry procedures are hard to fly. The difficulty lies with identifying the correct entry procedure for you inbound direction and working out the headings needed. It need not be said that the first few attempts will be difficult but as you repeat the exercise it starts to become more familiar and the mental workload decreases.

Start off by picking one holding pattern and keep flying this until you are happy with it. Work through all three entry procedures so that they become familiar and you become confident with what you are doing. When you are happy with this try a different facility - maybe the CAR hold.

If you practise initially with a VOR or NDB you have the advantage of seeing a needle in the cockpit show you are passing overhead the navaid. Holds at fixes are slightly more difficult in that you are usually looking for a DME reading to indicate the position. It can help in that more modern cockpits now have GPS to help visualise the situation.

What's a Procedural Approach?Types of ApproachBefore you startLearning the ChartSkills RequiredReference MaterialMoving onBefore we startFlying the ILSFrom VANINFrom IOM VORFrom RWY NDBFrom KELLYFrom CAR NDBTraining RoutesStarting the ProcedureTeardrop ProcedureFurther examplesHolding PatternsThe HoldHold Entry ProceduresSector 1 - Parallel EntrySector 2 - Reverse EntrySector 3 - Direct Entry