• What are IFR procedures?
• IFR procedure design (FAQ)
• Ask the procedure designer
• IFR procedure design 1
• IFR procedure design 2

IFR procedure design (FAQ)


The design of IFR arrival and departure procedures is the work of a procedure specialist. This person will design and check penetration of obstacle protection surfaces that encompass the entire IFR procedure. The safety buffer designed by the procedure specialist depends on the equipment being used (i.e. ILS, VOR, NDB, RNAV) and the phase of flight (i.e. approach, departure, missed approach etc.). The end of this process is a chart in the cockpit.

FAQs

Why does it take so long to design a procedure?

Firstly the data associated with the aerodrome is input into the computer. Navigational aids, runways and surveyed data is entered quite quickly but topographical information can take some time as it usually has to be laboriously digitised from hard copy maps. Digital terrain models are sometimes available but accuracy can be a problem. So it takes approximately 2 weeks to build a computer model of the airport and the surrounding area. The design of the IFR procedure is relatively straight forward and usually takes 1-2 weeks for a good design that takes into account all the requested parameters. There are software programs that will design a basic instrument approach in seconds, unfortunately there are too many variables for a software program to design an efficient instrument procedure at most airports. Finally there is the documentation that covers the design process, parameters used, calculations made, decisions and results found. This document is essential for checking the procedure, Quality Assurance and provides a background for the flight checking unit. This reference document can take up to a week to prepare. During this week an AIP ready chart is produced and checked.

Why do I need supporting documentation for the approach procedure, surely a chart is enough?

Supporting documentation is very important as it underpins the design of the procedure. This document details the parameters used in the design and the rational behind the operational decisions made. Without this document it would be impossible for the regulatory body (CAA) to check a new procedure without designing it all over again.

Why should an AIP chart be expected with a new procedure design, doesn’t the CAA make that when they publish the procedure?

The CAA usually do make the chart but that is part of the implementation process. Prior to that the new procedure needs to be checked and an aeronautical chart gives the checker an overview of the procedure. Also it makes the job of the flight checking unit much easier if they have an AIP ready chart to use in the cockpit when they are checking the procedure.

Why do we have to pay for these new IFR procedures, before the work was done for free?

Most CAA’s are now changing or have changed to being purely regulatory. Previously IFR procedure design was done by the government funded CAA. However now as a regulatory body the CAA can no longer design, check, approve and implement there own work.

For CAA’s that have not outsourced this service the backlog of procedure design work is extensive and is often measured in years not months. Private companies spend considerable amount of money on research and development to streamline the procedure design process and they are often able to complete a considerable amount of work in a short period of time.

How long do you train a procedure designer?

To start with the trainee should have an aviation background. Initially a procedure design trainee will be trained in “data entry”. This period of training will cover the following topics and take up to three months to complete.

Datums and datum conversions to WGS-84
Determination of relevant local datums
Topographical map theory and projections
Obstacle position tolerances in various situations
Creation and manipulation of databases
Working with 3 dimensional data
Manipulation and entry of digital terrain models
Correct scanning techniques and manipulation of raster images
Extracting relevant information from a survey report
Creating a quality control “Data entry” document

The later period of this training is OJT and all work is checked by the senior procedure designer prior to being sent to the procedure design section. At the end of this initial training period the trainee will attend an established 6-8 week basic procedure design course.

After the basic procedure design course is completed the OJT will continue for at least another year and all work is monitored by a senior procedure designer.

Should the instrument procedures be checked if there is an incident?

Yes definitely, unless it is very clear that an IFR procedure is not involved (i.e. gear up). A large majority of aviation personnel think that aircraft fly exactly on a route. If the incident occurs to either side of the track then it is often put down to pilot error. This is sometimes not the case as there are tolerances laid down by ICAO that ensure a 95% containment value in normal operations. For example the lateral tolerance of a VOR/DME track, in terminal airspace, is 11.3 km at a DME distance of 15nm. The supporting procedure design document should detail these areas and show that the obstacle/terrain were correctly accounted for.

How can changing IFR procedures in the air affect an airport?

A factor that has entered the equation recently is the privatisation of many airports and the emergence of low cost airlines. The viability of an airport depends not just on ground facilities (terminal buildings, baggage) but also airborne aspects. Arrival/departure delays, excess miles flown and high minimums resulting in diversions can greatly affect the attractiveness of an airport. Airport operators should look at the airborne side of operations as closely as they look at the ground based operations. Unfortunately this is very rarely the case.

Can emissions be reduced with a redesign of an existing procedure?

Most certainly yes.

Take the example of a single newly designed departure procedure at a busy hub airport that takes into account the advantages of RNAV and reduces track miles flown by just 2nm. Also let us combine this with a complete work over of a procedure at a medium sized destination airport, for example Tirana airport where 45nm was saved on one arrival. Combine this with the fact that the approach has been optimised to be flown as a Continuous Descent Approach (CDA). A saving of 360 lbs of fuel on a single approach was achieved in CDA trials done by UPS in the USA. Using a low altitude fuel burn of 2.5 gallon / nm we can do the calculations:

Departure
2nm Saving on 1 set of quadrant departures
20nm 10 flights a day on those SIDs
7300nm Saved in 1 year
18,250 gal fuel saved
Arrival
45nm Track miles saved on the approach
112.5 gal fuel saved from less track miles
54 gal fuel saved from a CDA approach
166.5 gal Total saved on 1 approach
499.5 gal 3 flights a week
25,974 gal Yearly fuel saving

44,224 gal Total fuel saving

The previous calculations are based on the assumption that it is IMC every day which we know is not the case. However for safety reasons many major airlines require their pilots to follow a published instrument procedure even in visual conditions.

These basic calculations show that a minor procedure design change at a busy airport on a departure and a comprehensive change to one approach at a medium sized airport could save an airline 296,300 lbs of fuel and subsequent emissions. What could the savings in fuel and emissions be if all IFR procedures at the major airport and at another medium sized destination airport were optimised?

Ian Whitworth MRAeS
Managing Director
ASAP s.r.o. (Aeronautical Services And Procedures)
Voice/Fax + 421 33 640 8470
Web page http://www.asap.sk