View Full Version : If And Iaf

8th Jun 2004, 08:28
guys, what is the difference between IAF and IF? what can't we do after IAF, what can't we do after IF? THANKS!!

8th Jun 2004, 12:43
Short reply: IAF is Initial Approach Fix. It marks the start of the Initial segment of the approach. IF is the Intermediate Fix, which marks the start of the next, or Intermediate segment. For completeness, though not in yr question, the start of the Final segment is marked by the FAF or Final Approach Fix.

PANS-OPS refers. It's not so much a matter of what you can do at each stage, as how the obstacle clearance changes as you get closer to the runway.

9th Jun 2004, 13:40

the application of 'approach ban' varies from country to country and could be related to the beginning of or a point in the approach, or could even be an altitude.

9th Jun 2004, 15:02
You'll see from other threads that various people/ fleets use the FAF for different things. Approach Ban may be one of them (but only if you consider the FAF to be the "OM equivalent" position).

My answer was left open for that reason. There's nothing universally true that must be done at or by that point, I believe.

11th Jun 2004, 15:51
Just to add a little more... the IAF marks the point at which the Pans Ops (or any lower) speed limits come into force. The IF will also tell the pilot that the next fix will be the FAF, where an even lower speed limit will apply, therefore the pilot might need to start slowing down from the maximum speed that is permitted in the Initial Approach segment.

Additionally, the IAF marks the point at which the width of the protection area reduces from the width associated with the enroute phase of flight. Depending on whether or not a STAR is used to join the enroute and approach segments, there may be other changes as well (ie secondary area).

The IF then marks the point at which the width of the lateral protection area progressively reduces even further. And, of course, the FAF marks the start of a further, progressive width reduction occurs. Thus, the pilot MIGHT see obstacles at a rather closer range, without getting toooooo nervous about them!

11th Jun 2004, 16:43
Can someone answer this.

In the UK the Missap procedure is drawn at 185KTS (according to the pans ops differences), does that mean we should be flying the Missap at 185KTS unless the plates say's something different?

12th Jun 2004, 12:11
I know nothing about the UK rules but, if the missed approach is based on a max IAS of 185, then that is your maximum speed - unless a lower speed is shown on a specific chart.

14th Jun 2004, 11:25
LYKA - Drawn where? In the AIP Charts? Or for the actual procedure calculations? Actually, it doesn't really matter, to answer your question. The procedures are calculated assuming the speed ranges appropriate to the aircraft category.
The 185 kts you quote would be the max speed during the intermediate "phase" (see PANSOPS for definition) for a Cat D aircraft.
That means "just what it says on the tin" - you can use any speed up to that maximum and you'll be covered in terms of obstacle clearance. If you need to use a higher speed, you should use the procedure for the next category up.

15th Jun 2004, 09:00
I might have to beg to differ with you, keithl, on that final point. Unless the UK rules differ from Pans Ops in this regard, if the max IAS is shown as 185 knots on the chart, there's no way to avoid it at all. That is the maximum speed that a pilot can use, regardless of category.

The MDA (or DA) might be slightly higher for a higher category, but this will not guarantee obstacle clearance in the missed approach, at any speed above 185 knots. Indeed, if the reason for the speed limit is to restrict turn radius, the use of a higher speed could remove the aircraft from the protection area.

15th Jun 2004, 10:43
OzEx - Always a pleasure to debate with you - I know you don't indulge in the invective that too often infests these forums!

Here's where I'm coming from: The only place I could find 185 Kts quoted was in PANS-OPS Table III-1-2. It's under "Max Speeds for missed approach", Category D, Intermediate.

I did say in my post that it was a maximum speed, so the normal meaning of that would be that you can use lower.

I think where you take issue with me is that if it's a maximum, you can't use higher regardless of aircraft category . Yet the max speed for the same phase, for a Cat E aircraft is given as 230kts. So much for the calculated speeds.

Now, "185 kts on the chart". Chart conventions vary. I know Aerad best, and they use 180kts for turning circles on approach charts (including MAP) and that is regardless of category. I've looked in Jepp. but can't find what speed they use. Perhaps someone here could oblige?

But I believe, as conventions vary, and because the speed info is not clearly displayed, that you can't treat chart diagrams as limiting, only performance calculations.

What do you say?

15th Jun 2004, 13:05

UK AIP GEN 1.7 - Differences from ICAO Standards, Recommended Practices and Procedures

DOC 8168: Procedures for Air Navigation Services - Aircraft Operations Volume II (Construction of Visual and Instrument Flight Procedures) (4th Edition)

Part III Chapter 1
1.9.2 Procedure Speed Restrictions. Unless otherwise stated, procedures are speed restricted to a maximum IAS of 185 kt.
Part III Chapter 7
7.3.2 Turn Paramters - IAS. Unless otherwise specified, all missed approach turns are limited to 185 kt IAS maximum.

This is not a speed category specific limitation. I once asked someone in my company's performance dept. and there was an explanation as to why we weren't speed limited to 185kts in operation. I think it was along the lines that each approach procedure was individually checked out for each aircraft type using that type's SOPs and speed / perf characteristics and so the "generic" restriction of 7.3.2 didn't apply. The legal framework for that is probably buried within the AOC. Or else the "unless otherwise stated" bit - anyhow the CAA FOIs seem happy with it (for all UK airlines...).


15th Jun 2004, 14:55
Got it! Thanks NW1, although you'd have saved me a bit of time if you'd said GEN1-7-29 ...

15th Jun 2004, 15:10
You're welcome. Try www.ais.org.uk if you want the whole document in PDF, handy for doing word searches when you need a specific reference....

15th Jun 2004, 21:17

Thanks old boy, this exactly what I was referring to. Any ideas or answers?

15th Jun 2004, 21:46
the CAA FOIs seem happy with it (for all UK airlines...).
This would seem to indicate that the UK procedures are designed using the max IAS for the approach category of aircraft, but the speed restriction is for airspace/ATM requirements (i.e. not obstacle clearance purposes).

15th Jun 2004, 23:21
Further to NW1's post:

'My' UK Airline teaches us not to exceed 185 knots during procedural Missed Approach in UK airspace and the reason given is the AIP differences from ICAO references mentioned.

The issue I have with this is that the differences are only filed with reference to Pans Ops II, and there are no filed differences to Pans Ops I which as far as I understand it is the book that tells us as pilots what to do. And on a practical level it could mean flying around with loads of flap out.

So I'm interested to hear that at least one UK operator doesn't agree with our training department!

Does anyone know the full answer to this? It seems strange to me that the AIP should half-heartedly imply a 185kt restriction, which some do, and some don't enforce, and that our plates make no reference to it and are emblazoned with 'PANS OPS 4' along the edge.

16th Jun 2004, 04:25
Technically speaking the UK is not obliged to file a difference from PANS OPS, as it is an ICAO manual, not a Standard (i.e. Annex). Vol I and Vol II are part of the same manual - the procedures are designed (or not) to the criteria laid down in Vol II.

16th Jun 2004, 09:42
It now seems clear that the UK AIP states that a maximum IAS of 185 knots is imposed on all missed approaches (unless lower is specified on the chart, of course). This tells me that anyone who uses a higher speed in the missed approach will run the risk of infringing airspace that must be avoided - or get too close to an awkward hill. I wouldn't be brave enough to use a higher speed, whether the company allows it or not!

If, as stated, the CAA FOIs are happy with a higher speed, I'd suggest that they probably don't know much about their own AIP, let alone Volume 1 of Pans Ops. I have my doubts that the CAA actually tests each new procedure for all speed categories at normal speeds. That would not seem to be required by the AIP reference but, oh yes, we ARE talking about the UK CAA aren't we... :}

keithl... I hear you and understand where you're coming from. I offer the following for consideration.

Yet the max speed for the same phase, for a Cat E aircraft is given as 230kts. So much for the calculated speeds.
I would venture to suggest that an AIP speed limit of 185 knots means that it affects Cat E as well - unless there's a note on the chart that specifically caters for Cat E. I can't see anything in the quoted AIP reference that alleviates this situation. There are no civil Cat E aircraft left now that Concorde has gone, but I guess that they probably fly Cat 3 ILS approaches everywhere in the UK, so a missed approach might be a bit academic.

Or it might just be that the UK AIP hasn't kept up with the latest procedure design practices. I suspect that, if I was working in the UK, I'd be seeking written clarification from the CAA.

Now, "185 kts on the chart". Chart conventions vary. I know Aerad best, and they use 180kts for turning circles on approach charts (including MAP) and that is regardless of category. I've looked in Jepp. but can't find what speed they use. Perhaps someone here could oblige?
I feel sure that charting conventions are adopted for ease of ensuring that all the charts are the same size and same scale. If they were to attempt to depict the actual speed then, in places where speeds directly reflect Pans Ops, either the chart size may have to be enlarged (ie not easily fit in the book) or the scale of the chart has to be changed to accommodate a huge turn radius. That wouldn't be efficient for a mob like Jeppesen or Aerad, I'm sure.

16th Jun 2004, 10:16
Thanks, OzExpat but I've withdrawn hurt, having started from the wrong place, as tactfully pointed out by NW1.

It does seem a mess, and if the aircraft I am concerned with were capable of 185kts in the Missed Approach I'd certainly be seeking clarification, that's all I'll say.