Approach category lesson

[riteortbit]

Just trying to figure out approach categories. Approach category is determined by Vat which is Vso x 1.3, Vso being stalling speed at max wt in the landing config. Question is, is Vso determined by the manufacturer (eg Airbus) at a standard atmosphere. Therefore is a base approach category determined by the manufacturer. Further is that category possibly changed eg from C to D by the airline ops depending on their own self imposed safety margins. Would the PIC on the day decide to fly a higher category (C to D) depending on weather and weight. In practice is all this hypothetical and what the manufacturer determines is what goes? Several questions there, in particular I'm interested in an A320. Thanks for any explanations. (Confused ATCO)

[FlapsOne]

It's not quite so straightforward - what a surprise.

Some notes from PANS OPS and the Airbus manuals

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Vat - Speed at threshold based on 1.3 times stall speed Vso or 1.23 times stall speed Vs1g in the landing configuration at maximum certificated landing mass.

The landing configuration which is to be taken into consideration shall be defined by the operator or by the aeroplane manufacturer.

Because aircraft of the A320 family have a low-speed protection feature (alpha limit) that the flight crew cannot override, the airworthiness authorities have reconsidered the definition of stall speed for these aircraft.

All the operating speeds must be referenced to a speed that can be demonstrated by flight test. This speed is designated VS1g.

Airworthiness authorities have agreed that a factor of 0.94 represents the relationship between VS1g for aircraft of the A320 family and VSmin for conventional aircraft types. As a result the authorities allow aircraft of the A320 family to use the following factors :

V2 = 1.2 × 0.94 VS1g = 1.13 VS1g

VREF = 1.3 × 0.94 VS1g = 1.23 VS1g

These speeds are identical to those that the conventional 94 % rule would have defined for these aircraft. The A319, A320 and A321 have exactly the same maneuver margin that a conventional aircraft would have at its reference speeds.
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So the PIC really cannot (should not??) just change it a it is a declared figure.
Hope that is of some help

[riteortbit]

If I'm reading you right that means an A320 could fly to Cat C minima when the IAS crossing the threshold would suggest that it should be flying Cat D??

[riteortbit]

If I'm reading you right that means an A320 could fly to Cat C minima when the IAS crossing the threshold would suggest that it should be flying Cat D??

[alatriste]

A 320 will always fly to CAT C minima regardless of :
weight, temperature,wind,QNH,elevation or indicated airspeed on short final.
The previous poster was right regarding A 320 stall speed calculation, though a littel bit out of the topic.
CAT is based on REF SPEED (1.3 Vs or 1.3 Vsr/Vs1g) at max certified landing weight. It will depend on aircraft characteristics,for instance a not very heavy aircraft like the CRJ is CAT D cause the ref sped is high due to the lack of slats. As a rule of thumb the heavier aircraft type the higher category.
A 320 CAT C., A 321 CAT D

[FlapsOne]

Vat Cat C 121-140 kts
Vat Cat D 141-165 kts
A319 @ Max LDG Wt has Vref 130 kts = C
A319 @ Max TO Weight has Vref 134 kts = still C
Anyone got a 320 QRH handy for the others??


edited cos I screwed up the numbers!

[alatriste]

A 320 Vref 134 KIAS at MLM (64.5 T) CAT C.

[OzExpat]

It's not just that.
Have a look at the speeds that are declared for the various phases of the approach. In particular, look at the speed for circling. The operator must be able to meet ALL the speeds in ALL the approach phases, including circling, to be able to claim a particular approach performance category.

It matters not whether the operator decides that the particular aeroplane type will never circle. The fact is that all aeroplane types are capable of circling and, unless your company holds some sort of exemption from its regulator, it MUST meet all the criteria. If it doesn't, the company's insurance is on the line, so guess what that means for the flight crew. :eek:

[FlapsOne]

ICAO DOC 8168 Section 3
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1.10.5 The ranges of speeds (IAS) in Tables III-1-1 and III-1-2 take account of the handling speeds when aircraft perform the manoeuvres specified and are to beused in calculating procedures. For conversion of these speeds to TAS, see Attachment F to Part III.

1.10.6 Permanent change of category (maximum
landing mass).
An operator may impose a permanent, lower, landing mass, and use this mass for determining Vat if approved by the State of the Operator. The category defined for a given aeroplane shall be a permanent value and thus independent of changing day-to-day operations.

1.10.7 Where airspace requirements are critical for a specific category of aircraft, procedures may be based on lower speed category aircraft, provided use of the procedure is restricted to those categories. Alternatively the procedure may be specified as limited to a specific maximum IAS for a particular segment without reference to category.

Also from 8168
Note.- The Vat speeds given in Column 2 of Table 111-1 -1 are converted exactly from those in Table ill-I -2, since they determine the category of aircraft. The speeds given in the remaining columns are converted and rounded to the nearest multiple of five for operational reasons and from the standpoint of operational safety are considered to be equivalent.
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[390cruise]

alatriste

I think you will find that the early A321 with MLM 75,500 Kg are still Cat C,
however the Heavy Weight A321 with MLM above 75,500 Kg are Cat D.

Regards
390

[riteortbit]

Thanks for the replys. I think I've spoted the source of my confusion. Please correct me if I'm wrong here.
The aircraft comes from the manufacturer certified to a specific approach category
the operator may have the aircraft recategorised with the approval of the State
The pilot may fly a different approach category profile on the day but still operate to the minima determined by 1 or 2 above

[Clandestino]

1. it doesn't
2. it can't
3. (s)he can try. Luckilly, most procedures are cat D capable so not much harm can be done. But on the odd day, at the odd airport by using higher cathegory speed with lower category minima/procedure, (s)he will bust his/her obstacle clearance and than the day will be saved by the (E)GPWS. Or it won't.
Your approach category is based on what speed you can safely maintain for your given weight and your given configuration. E.g. empty 747 (min fuel and no payload) has Vat lesser than 120 kt, so it can use cat B minima but loaded it will have to go into cat D. ATRs I've flown were cat B with two exceptions: cat C minima were to be used for circling as our minimum circling speed was set to 140 kt by our SOPs (above 135 for cat B) and at MLW in icing conditions, Vat was 122kt, busting max B speed by 2 kt.
A320 with landing conf 3 or 4 is generally cat C compliant. 321 might go over threshold faster than 140 kt so it will be cat D. And with flaps and slats stuck retracted, it can easily slip into cat E, right along F-104s and MiG-21s.
However, in the world of 3000m or longer ILS equipped runways and no significant obstacles around airport, approach categories are of academic interest only. This might explain some explanations around.

[FlapsOne]

Well ICAO 8168 says the category is based on the maximum landing mass and not what you can 'safely achieve' at the time.

What is your source for that statement?

[Clandestino]

Here's me getting it wrong again. :O

Indeed categories are fixed by Vat at MLM and landing config

So answers:

1. it does
2. it can
3. oh well, you can always use higher cat minima with lower cat speeds but not vice versa.

A320 could fly to Cat C minima when the IAS crossing the threshold would suggest that it should be flying Cat D??

Now that's the one that made me rant insanely and claiming that approach categories are not fixed. If you have to use speeds for higher cat, then you have to use minima for that category too. As for using lower category minima if your MLM is low enough to put your speeds in lower cat range, while I can't think of any reason why it shouldn't be allowed, it's very probable I don't know the whole story. Chances are that it's best to err on the safe side.

Apologies to everyone that might be mislead by my previous post.

[Amateur Turbines]

Hello all, this is an interesting debate. Our company in Canada ran into this one recently. We came to the conclusion that this was not possible ie flying a lower speed in order to meet lower cat and hence lower mins. The reason that we came up with (although not written any where in our CARS) was the missed approach requirements. Our Vxse is 122 and therefore Cat C even if we flew approach to Cat B mins we could not do missed approach in the Cat B speed range. What do you think of my companies conclusion to this?