CAT Approaches

[R200EGNM]

Hiya,

I was wondering if someone can tell me how you work out what CAT an approach is?

For example at SS the minima for CAT A,B,C and D all have the RVR 700 meters so whats the difference between them?

Thanks for your help

[FlapsOne]

You'll find those letters refer to the category of aircraft not the approach.

Your approach speed at MAUM will determine the aircraft category.

[OzExpat]

Find the information in ICAO Doc 8168 (Pans Ops) Volume 1 or 2. The relevant stuff should also be repeated in your country's AIP.

[Scallywag]

R200EGNM, the aircraft category is based on the nominal threshold speed, and defined as 1.3 X stall speed in landing configuration at max landing mass. (1.23 X VS 1g for JAR 25 aircraft)

A <91 Kt
B 91-120 Kt
C 121-140 Kt
D 141-165 Kt
E 166-210 Kt

Cheers, Scally

oops, edit for typo.

[john_tullamarine]

The principal concern is that speed determines a reasonable minimum turn radius which determines how close-in a pilot can reasonably manoeuvre his/her bird in poor weather.... this, in turn determines the area around the airport which has to be considered for circling etc obstacle problems ....

The slower manoeuvring Cat A lightie can keep in much closer than can the higher speed Cat D/E heavy metal ... and the Cat A protected areas are appropriately closer in to the airport.

Perhaps OzExpat, who knows about such things, might be a nice chap and elaborate on the general "of pilot interest" details ... ?

[spekesoftly]

Reminds me of a scenario that happened many years ago. Airport 'A' was receiving lots of diversions due to a 'little local difficulty' at nearby Airport 'B'. The Wx. at 'A' was low cloud, reasonable vis. below, and a strong tailwind on the only ILS equipped runway. The radar at 'A' was u/s, so aircraft were making procedural ILS approaches and then a visual manoeuvre to land opposite direction, and into wind. Watching many of the larger jet aircraft wizzing past at low level, and then banking tightly onto final was interesting, and probably qualifies for an entry on the 'What was the best airshow' thread!!

One foreign military C130 had turned so violently, that the aircraft was subsequently grounded until engineers had checked the airframe for overstress! :rolleyes:

[R200EGNM]

Thanks a lot for your help :D

[OzExpat]

Yes john_t, I should've been watching this thread more closely. The story is a tad more complex than Scallywag would have you believe, which is why my first post aimed our friend R200EGNM at the complete reference.

The ICAO Aircraft Performance Category system is designed so that each aircraft type fits neatly into only one category. It is true that the first assessment is based on the speeds quoted by Scallywag, but one must then look at all the other associated performance data for that category. There are, for example, any number of aircraft types that would, on initial assessment, fit in Category "B". However, they end up in Category "C" because of something simple like indicated airspeed for circling.

So, even though all other parameters might fit for Cat. "B", if there is just one parameter that can't be met, the type must be classified in the next higher category. PNG would be one of very few countries still operating F-28 aircraft types; this is the type I was specifically referring to above - a very flexible aeroplane but it's normal circling configuration requires a circling speed higher than that for Cat. "B".

Note, too, that ICAO does not allow reduction of category. This is why one must look carefully at all the required performance parameters that apply to each category. As far as I'm aware, most single-engined aircraft will readily fit into Cat. "A" and most of the light piston twins fit in Cat. "B". The performance problems only start to affect things with the higher performing, slippery types.

And, yes, as john_t correctly points out, it's turns that make the biggest difference in the size of the protection area for any segment of any instrument procedure. A reduced airspeed will produce a somewhat reduced radius of turn, but use of a steeper bank angle has a greater effect, even without reducing speed. This might seem like an academic point but, obviously, if you can safely manoeuvre your aeroplane at a speed lower than that specified for your aircraft category, or at a steeper bank angle - or a combination of these - your aircraft will be contained well within the protection area provided for your category of operation.

That makes you safer than a pilot who simply uses the minimum performance parameters specified in Pans Ops. Yes, in theory, both you and that other pilot will still be safely contained. But the aircraft that can safely maneouvre more closely within the parameters has more room for error.

For example, if the minimum performance in a segment requires an average bank angle of 20 degrees (and all bank angle requirements are averages) its really better to shoot for 25 degrees of bank as your own consistent average. If you don't quite achieve it, or can't maintain it for long enough, you will probably still be within the 20-degree average. And, after all, its a bit hard to determine, in flight, if you've actually met an average bank angle requirement.

And, lets face it, the closer you are to the weeds, the more important this becomes, whether you're in IMC or circling in poor vis.

[Scallywag]

Oz, I wasn't inferring that it isn't a complex subject, merely giving a simple answer, as I think, from the tenor of the question, that is what R200 wanted. Plus I've only got ops manual, not ICAO to hand ;) Thanks for your interesting amplification.