View Full Version : Approach Catergory

Captain Smiley
26th Mar 2004, 01:44
There is some dicussion at my company concerning which Catergory our Dash-8s fit into on a circling approach.

Our company profile is to fly the aircraft clean (gear and flap up) at 140kts until visual with the runway. When and if visual the flap and gear are extended and the speed reduced to 120 kts.

Normally we consider the Dash 8 to be a Cat B aircraft but on the Jeppesen plates there is a note saying 135kts max under circle to land minima Cat B. Does this mean that we are Cat C because of our company profile?

My belief is that the aircraft is still considered Cat B since the 135 kts max applies to the visual manoevering segment of the approach.


26th Mar 2004, 03:09
I think your question is must you use the higher minimum if the higher airspeed is used only before maneuvering.

When you begin an approach and plan to circle, I believe that you use circling minima. If you are at 140 kts, yet fly to the MDA for 120 kts, that seems to be contrary to the Jepp published minima. In fact, this would be contrary to what many operators are doing these days. That is, many have the pilot fly to the highest minima published for the circling approach. The reason for this is because otherwise a circling approach delivers the aircraft to low speed maneuvering at low altitude, in poor visibility at a time of high cockpit workload. At this point your company wants you to configure and change airspeed while maintaining visual with the runway?

26th Mar 2004, 20:20
I'm not sure if I've got the right sort of category here. Are we talking about 'aircraft approach category' which is part of the FAA definition to classify the airport? If not, and it is some instrument flight category, then please disregard the rest of this post.

If it is the FAA airport classification, then the Dash 8-300 is classified by the FAA (reference: AC150/5300-13 Airport Design) as A-III, which is aircraft approach category A.

The basis for their classification is the aircraft approach speed, and the limit for aircraft approach category A is <91 knots. The aircraft approach speed is defined as 1.3 times the stall speed in the landing configuration of aircraft at the max certified landing weight. I'm not sure what the stall speed of the Dash-8 is, but the FAA has the approach speed stated in their database as 90 knots. The Cat B limits are 91-<121 knots and Cat C is 121-<141 knots.

Even if the aircraft approach category was to change from A to B for some reason (while staying aircraft design group III), there would be no change in the airport standards (FAA Table 1-1 in AC150/5300-13). It is only moving from Cat B to Cat C (while staying aircraft design group III) that means a step up in terms of the runway strip (the FAA call this the runway safety area). The runway now has to be less undulating and have flatter gradients. However at 9 out of 10 airports, you’d be hard put to pick the difference. The 10th airport is probably one of those spectacular Dash-8 airports up the side of a mountain or similar.

27th Mar 2004, 13:42
I believe the following information to be reliable in that it originates from ICAO PANS-OPS.
The design of takeoff, approach, and landing procedures is governed by the aircraft classification (A - E). This classification is based primarily on the threshold speed (Vat) which is 1.3 x stall speed (Vs) for the maximum certificated landing mass. Note that some operators have lower landing wt certification for noise / en-route / landing fee reduction. I don’t know of anyone who has done this for approach criteria, but there has been discussion between an operator and authority re landings on short / low strength runways. Thus same version of aircraft as well as different versions may not have the same approach category.

Also note that some aircraft will have a higher category than specified by Vat due to the speeds that have to be flown during a procedure because of the aircraft design (N.B. abnormal configuration operations / icing limits).

Thus for a MLW Vat of 120 kts the aircraft would be Cat B, but all categories also considers the maximum takeoff speed (165), the range of speeds for the initial approach (120/180, but 140 for reversal / racetrack), the range of speeds for final approach (85/130), maximum circling speed (135), and the maximum speeds during ‘intermediate’ and ‘final’ missed approach (130 and 150). All examples ( ) relate to Cat B.

Some approaches are specifically defined for lower speeds, these must be followed. From Captain Smiley’s question and his reference to a speed limit in Jeps I suspect that this is the limiting factor. Therefore whilst the aircraft is Cat B, it would be incorrect to fly the 140 kt SOP speed on any procedure with a lower speed restriction. Note that the procedure is owned by the national authority of the country who licenses the airfield, thus it may be inappropriate to seek a dispensation from your own authority or inspector as they may not have the relevant information

Also beware that for procedures designed by TERPS (US) whilst generally giving the same obstacle clearance, the circling and maneuvering areas may differ significantly; e.g. 767 CFIT at Busan Korea during circling procedure.

Edit: threshold (Vat) replaced touchdown

27th Mar 2004, 15:33
This is testing the ol' memory a bit. I flew the Dash 8 briefly in Oz. It's a Cat B aircraft. If we wanted to fly it faster for whatever reason in the approach/circle to land then we'd have to use the Cat C requirements so we remained in the protected area.
Have a squizz at the charts to see what the circling minima is and stay within that for Cat C. That should keep you safe and away from the ground/terrain.

30th Mar 2004, 07:54
When the Pans Ops speed classification system was introduced, both here and in Oz, there was a fair degree of confusion on this point. The basic situation here is that, if you can't meet ALL the requirements of the nominal category, you must use a higher category that allows you to meet all the speeds. Circling was certainly the major issue for many aircraft that are nominally in Cat. B, so they all had to use Cat. C.

And, before anyone asks, no you can't use a lower category on the basis of speeds for actual configurations. I understand that ICAO is about to change the basis of the speed categories in the near future, but it isn't likely to change the speed requirements in any of the segments.

31st Mar 2004, 13:16
For a circling approach the DHC8 can be flown using CAT A speeds (we use circling speed of max 109 knots for precision circling, and the minimums are determined "-100 minimums" because they are aircraft specific). It really doesn't matter which aircraft you fly; it's the speeds you use that matter. On a CAT B approach you must stay below the maximum of 135KIAS when reaching minimums. Note that the Categories with reference to 1.3 Vs are different from the categories concerning the approach itself. If an apporoach is labelled 'CAT B only'; any aircraft can fly it, provided they'll remain at or below 135KIAS (or, say, 130KIAS for the MAPt).

Bomber Harris
1st Apr 2004, 02:44
crossunder. what you say makes a lot of sense. but i would tend to lean towards what 'alf' posted. when this is analysed at the 'subsequent board of enquirey' the legal definitions will be what counts. i would take adhereing to those as the first and formost rule. i.e. if the 1.3 rule makes an a/c cat b but it can be safely operated at cat a speeds....then it is still cat b because thats what the definition says. however, what redsnail says rings some loud bells for me too. i think it says somewhere that if a condition exist which will not allow you to keep to speeds...in my example...cat b then the approach must be done to cat c minima.

apologies if i have misinterpreted what you were saying and answered the wrong question!!....complicated issue

1st Apr 2004, 08:15
If an apporoach is labelled 'CAT B only'; any aircraft can fly it, provided they'll remain at or below 135KIAS (or, say, 130KIAS for the MAPt).
Definitely not true and potentially quite a dangerous idea to try to circulate. It demonstrates a complete ignorance of Pans Ops Volume 1, if nothing else. It doesn't matter what speeds any particular aircraft can achieve, if below any of the speeds for the nominal category.

I know that the Dash-8, for example, is a very flexible aeroplane. No doubt about that.

But lets take the example of a very flexible type of aircraft that is nominally in Cat C. It doesn't matter if it can maintain 130 KIAS or below, from the FAF to the MAPt. It also doesn't matter if it can maintain 130 KIAS or below for circling. This is because the determining factor for this aeroplane is the basic 1.3 Vs at max certificated weight.

The same sort of consideration applies to all other aircraft in all nominal categories. Thus, getting back to the Dash-8, it is a Cat B aeroplane, regardless of what aspects of Cat A it can achieve.

1st Apr 2004, 08:46
In accordance with the All Weather Operations (JAR-OPS Subpart E)

Your aircraft is Category B, come hell or high water! The Category B classification is based upon the Vat (ie: across threshold and NOT at touchdown as suggested above) being 1.3 times the stalling speed (Vso) or 1.23 times Vs1g at MCLM in the landing configuration. You cannot change that.

With regards to which minimums are applicable: your company needs to operate according to the manufacturers certification speeds and should make use of the procedures and techniques certified by the manufacturer for circling (and other) approaches in order to remain within the bounds of Category B operations. Flying a higher speed however, makes the higher circling minima applicable.


1st Apr 2004, 09:34
A question - and sorry for re-starting a tired thread; I've just come across it.

The rules in this country (NZ) allow an aircraft to fly to a higher category, provided ATC knows about it. But how would one go about telling them?

"Request ILS 23L, and aaah we'll be Cat C today."

AFAIK one simply operates to the category one feels like operating to (higher not lower), and obeys speeds & minima for the new category regardless of aircraft type - and who cares?

1st Apr 2004, 13:39
The rules in that country do nothing of the sort! Cat B is Cat B and Cat C is Cat C etc. and you are not able to re-classify the aircraft just because you feel like it! Read the rules again!

Of course there is nothing stopping you flying whatever speeds you like, as long as you apply the correct minima. And why would you need to tell ATC about that?

2nd Apr 2004, 12:58
Most countries that I'm aware of require you to tell ATC. It is relevant to their assessment of the cloud base in clearing you for the approach. Pans Ops isn't the only yardstick in operations! :)

The post by 126.9 is interesting from the point of view of the design of the procedure. If what was posted is correct, there is no flexibility for a higher category, based on the maximum speeds within a specific category.

For example, I once had a bit of a dilemna with the F28 because, in theory, it could achieve Cat B in everything except circling. That made it Cat C. That's the category that's used by this type to this very day but, if I understand the post by 126.9 correctly, there is one ICAO-contracting State that does not abide by this. I just hope that the AIP (or Regulations) reflects that. :}

3rd Apr 2004, 09:30
Thanks for the replies.

126.9 - hmm, fairly severe misunderstanding there.
No-one's talking about reclassifying an aircraft, but I did say "flying to a higher category", meaning "flying whatever speeds you like, as long as you apply the correct minima". Hope you recognise the similarity between those two quotes, mine & yours!

Unfortunately, still confused. Your comment re ATC makes sense OzExpat - have you ever actually told ATC you're operating to a higher category speed / minima?


3rd Apr 2004, 20:19
Not having flown the ‘flexible’ option described above, I assume that the notification to ATC also allows for the appropriate ‘straight in’ maneuvering allowance – higher MDA and greater visibility to counteract the higher speed. However this may not apply to circling.

Previously I referred to a CFIT accident in Busan Korea, a resume is here:- Busan 3.pdf (http://uk.geocities.com/[email protected]/alf5071h.htm).

Although the error in this accident was the assumption that PANS-OPS circling areas applied (4.2nm rad from t/h. Cat C) whereas the airfield was actually charted to TERPS (1.7 nm rad from t/h. Cat C), the issue of flight outside a safe area may also arise with increased airspeed.

A turn at 20 AOB 180 kts (Cat C) gives a radius of approx 1.4 nm; thus with TERPS this only gives a small safety factor for error, wind, etc; lower bank angles reduce this margin. Flying at Cat D speed – 205 kts the rad of turn is 1.8 nm at 20 AOB, which exceeds the TERPS area. These changes apply to PANS-OPS in a similar way, but the safety area is larger. Thus the aircraft category speed limit must be respected and there is also a minimum AOB to consider.

Many of the issues in this thread are presented in an excellent booklet ‘From Takeoff to Landing’ by Olle Akerlind who worked for SAS performance dept; there was a limited reprint by Honeywell last year, but it is not on the web.

4th Apr 2004, 05:43
Oktas8... no, I've never done that and I suspect that nobody else has done it either - at least, not in the course of normal operations. I suspect that the main reason for this provision is consideration of an abnormal operation. An example of this might be where a particular aircraft cannot use all the flap normally required for landing - thus, a higher approach speed is likely to be necessary.

With advance notice of this, ATC can assess weather conditions against the higher MDA and advise the pilot accordingly. If the weather isn't good enough for that higher MDA, the pilot has a bit more time to plan for an alternate approach, or alternate aerodrome.

alf5071h... I was going to download that Busan report, but got a message saying I need to download some sort of graphic rendering utility. Couldn't be bothered with that on this low speed, high cost dialup access. Anyway, I have an idea that the FAA is starting to rethink the size of TERPS circling areas, so we may see a significant enlargement at some stage, so that they'll be more in line with Pans Ops areas.