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 John Woodside

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.

The following four pages can be downloaded as a DOC file for printing - FST_IAP.ZIP

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.

  1. 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.

  2. 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.

  3. 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.

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