Approach minima question

[Flamin_Squirrel]

Hi guys.

I hope the following isnt a stupid question :O

I (think) understand the idea behind CAT I, II & III ILS landing minima, I was just wondering how the CAT A, B, C & D fit in in the following approach plate.

http://www.nats-uk.ead-it.com/aip/current/ad/EGSS/EG_AD_2_EGSS_8-4_en.pdf

[K.Whyjelly]

I (think) understand the idea behind CAT I, II & III ILS landing minima, I was just wondering how the CAT A, B, C & D fit in in the following approach plate.

Landing minima are established for six categories of aircraft; ABCDE and helicopter. An aircraft fits into one category or another based on its maneuvering speed. Maneuvering speed is defined as 1.3 times the stall speed at maximum gross weight in the landing configuration. The table below identifies the Category vs. Maneuvering Speed.
Approach Category Speed (Knots) A- 0–90 B- 91–120 C- 121–140 D- 141–165 E- Abv 165

[Flamin_Squirrel]

Sorry I should have been clearer, I know where the CAT A, B, C, D etc came from, I was wondering how that fitted in with the CAT I, II, III ILS minima.

Example, if you're on approach in a CAT D aircraft is your minima 200ft radio or 450ft baro?

[K.Whyjelly]

Obstacle clearance altitude OCH is the height on an IAP with the minimum
permitted clearance above obstacles on the final approach. It does not take
account the limitations associated with the navaid (system minimum). Thus
the DH or MDH is the higher of the OCH or the system minimum. The OCA is
obviously the altitude corresponding to the OCH. Flying a cat 1 approach then your MDA(H) is based on your baro reading with a minimum of 200ft and 550m RVR. If you are flying a Cat2 approach then all minima is referenced to the radio altimeter not lower than 100ft. Cat 3a allows you down to 50ft RA and Cat3b down to 0ft (no DH) except in France and Switzerland where a mini DH exists for Cat3b approaches of 25ft

[Sepp]

First - an apology if this post contains omissions or errors - it's a complex subject to tackle after a long day! But I'll do me best...

Quick answer - neither! The plate you have posted shows only the OCH(A) - this is important information from the point of view of regulatory compliance, but is not used directly to describe "minima". The conventional DH for this app would be 200 ft baro (or DA 548 ft) for all a/c cats - and it just so happens that the RVR required (which may vary according to aircraft cat*) is 550m for all cats. Don't forget, too, that the minima will depend also on the lighting facilities that are available on the day, whether one's operating single/multi crew and, in many companies, who is doing the flying (experience, etc.) ... fun, innit?

*the Cat I, II etc. describes the capabilities and requirements of the system - ground aid, a/c equipment, crew qualification etc.. Cat A, B, C etc. attempts to describe the characteristics of the a/c - not only final approach speed, but also circling, intermediate approach and missed approach speeds are relevant. For apps with no FAF, there are also rate of descent limitations. Aircraft dimensions have a bearing on the appropriate OCH (at least for precision apps), and DH is derived from OCH plus a margin, the characteristics of which are described in ICAO Annex 6, I believe.

As you will have prolly realised, the relationship between all the various elements is complex, but there are nice diagrams in Jepps if you have access to a copy (vol I / ATC / ICAO procs / ICAO arr and app procedures / para 1.9.6.2, diag. I-4-1-2, 3 and 4 ) showing the relationship of OCH, thr elev, DH etc., for precision approaches, non-prec apps and visual manoeuvering, respectively.

Hope this helps - I'm off for a glass of vino. Cheers!

Sepp


edit/ sorry, K.Whyjelly - you beat me to it! :)