Instrument procedures

PANS-OPS vs TERPS: how instrument procedures differ

Every instrument approach you have flown was designed by someone working to a published set of criteria. There are two in common use: PANS-OPS, published by ICAO, and TERPS, published by the FAA. This page explains how they relate and, more usefully, how to find out which one you are flying.

By Matthew Dowell, airline training captain and examiner. Written in a personal capacity. This page draws on my book Flying Protected. It is an overview, not regulatory text: the criteria are revised, so check the current documents and the chart in front of you.

The two documents

Volume II of PANS-OPS and TERPS do the same job: they set the areas and obstacle clearance used to build a procedure. Both are public. Neither was written with the line pilot in mind. One line in the foreword of PANS-OPS is worth remembering: procedures designed to it assume normal operations, and providing for the abnormal and the emergency is the operator's responsibility.

Criteria travel; countries do not

TERPS is not "the American one". It is a body of design criteria, and a state may adopt whichever criteria it prefers, or adopt one set and modify it. Some states outside the United States design to TERPS or to criteria derived from it. Do not sort this by geography or continent: the useful way to think about it is that every aerodrome was designed to something, and you can find out which.

If you fly long haul, this is not abstract. It is ordinary to brief a departure built to one set of criteria and, ten hours later, an approach built to the other, with the same crew and the same aeroplane. Nothing announces the change. The charts look much the same, and the only thing that has moved is an assumption buried in the design.

Why they differ at all

Not from carelessness. Both sets are internally consistent and both produce safe procedures. They were written in different places at different times, solving slightly different problems, and they made different trades. Where the two diverge, TERPS has historically been the tighter of the two laterally, with smaller areas and less room around you. That is why the standing advice, when you cannot establish which applies, is to plan for the smaller one.

How to find out which applies

1. The state's AIP. A state declares its differences from the ICAO provisions in the general section, at GEN 1.7 and at ENR 1.5.1. It takes about ten minutes, and for most pilots the list of regular destinations is short.
2. Your operator's briefing documentation. It may well have done this for you already.
3. Chart annotations. Providers differ in what they mark and where, so learn what yours annotates. Treat silence as no answer.

Silence in the AIP is not agreement. If it says nothing, do not stop there.

When you cannot tell

Occasionally you will not be able to establish it: an unfamiliar destination, a late diversion, no time. The default is to plan for the more restrictive of the two. It sits inside the other, so planning to it protects you either way. This changes what you brief and where you set your triggers. It does not mean flying more tightly, more steeply or closer to anything, and getting that the wrong way round trades a threat you cannot see for one that is far more likely to hurt you.

From OCA to your minima

It is tempting to think the number the designer produces is the number on your plate. It is not. The designer's output, the obstacle clearance altitude or height (OCA/H), is a statement about terrain and nothing more. Between it and the minimum you fly sit system minima for the type of approach, your operator's approved calculation, any state or aerodrome additions, and equipment and crew status. You always take the highest. At a flat aerodrome the surveyed terrain may not be what limits you at all.

How this fits the ATPL syllabus

If you are studying for the EASA or UK CAA ATPL, the instrument procedures material draws on PANS-OPS ideas, mainly in Operational Procedures. See the ATPL Operational Procedures guide.

What is inside Flying Protected

Flying Protected explains how instrument procedures are built and what they assume about the pilot, in 29 chapters. It explains the concepts fully and skips the calculations: everything you need to reason about a procedure, and nothing you would need to build one. It works alongside your operations manual and never argues with it.

Part I: Foundations

• 1. Who writes the rules
• 2. What an instrument procedure is
• 3. Categories and speeds
• 4. Protected areas and obstacle clearance
• 5. Fixes, tolerance and turns
• 6. From OCA to your minima
• 7. Where the visibility comes from
• 8. When the visibility goes

Part II: Arriving

• 9. Arrival and sector altitudes
• 10. Holding
• 11. Reversal procedures
• 12. The intermediate and final segments
• 13. Continuous descent
• 14. Altimetry
• 15. What RNP actually means
• 16. The PBN approach and its minima
• 17. Flying an RNP procedure
• 18. Circling
• 19. The visual segment
• 20. The missed approach
• 21. Parallel runway operations

Part III: Departing and en route

• 22. Departure gradients
• 23. Departure surfaces
• 24. Engine-out
• 25. Noise abatement and your climb
• 26. En route minimum altitudes

Part IV: Using it

• 27. Reading the plate for clues
• 28. Briefing it
• 29. Quick reference

Frequently asked questions

What is the difference between PANS-OPS and TERPS?

Both are sets of design criteria for instrument procedures. PANS-OPS is published by ICAO as Doc 8168 and TERPS is the United States standard published by the FAA as Order 8260.3. They do the same job and reach the same destination by different routes, and occasionally at a different answer.

Which countries use TERPS?

TERPS is a body of design criteria, not a country. The United States designs to it, and some other states design to TERPS or to criteria derived from it. Which one applies is a property of the state, and the state's AIP is the answer, so check it rather than assuming by geography.

Where do I find out which criteria apply?

A state declares its differences from the ICAO provisions in its AIP, in the general section at GEN 1.7 and at ENR 1.5.1. Your operator's route or airfield briefing may already say, and your chart provider may annotate it. If the AIP is silent, silence is not agreement.

What if I cannot tell which one applies?

Plan for the more restrictive of the two. It sits inside the other, so flying to it protects you either way. That is a planning decision about what you brief and where you set your triggers, not a reason to fly more tightly, more steeply or closer to anything.

Do I need to know both for the ATPL exam?

The EASA and UK CAA ATPL syllabus draws on PANS-OPS ideas in the instrument procedures material, mainly in Operational Procedures. TERPS is not the focus, but knowing both helps if you will fly to or from the United States.