View Full Version : CS-AWO and operational practices

17th Mar 2011, 01:50
Just a Flight Instructor here, so I am not working with this in daily business. But my curiousness regarding CAT II/III ops and certification standards begs me to ask.

Referring to CS-AWO 321-Installed Equipment for DH 50 ft or greater, there are three suggested setups, in a nutshell:

1) Fail-passive automatic approach system without automatic landing, 321(b)(1)
2) Fail-passive automatic landing, automatic go-around, 321(b)(2)
3) Fail-passive automatic landing, manual go-around, 321(b)(3)

Referring to CS-AWO 304-Control of flight path and ground roll

(a) The primary mode of controlling the aeroplane must be automatic until the main wheels touch the ground (except as in CS-AWO 321(b)(1)), and for operation with no decision height, control must be automatic until the nose wheels touch down

So the question is, can you get CAT IIIA approved without autoland function? Thinking about scenario 321(b)(1). How far down the approach (until contact?) do you need to use automatic approach system? I know the EU-OPS requires auto-coupled approach to an height of 80 % of applicable DH for the minimum RVR values to apply.

I understand their may be many different variations out there under different certifying authorities. I seem to recall, some time ago, someone writing the EMB170 approved for handflown to 50 ft DH using HUD. Could be wrong though.... I just don't grasp the big picture..... :)

Appreciate any help in this matter!!

17th Mar 2011, 02:57
i think alaska airlines had a HUD setup on their 727's for a manual flown and landed cat 3a so it can be done.

remember, the way the manufacturers and airlines do it...is the cheapest way they can get it certified.

autolandings can be nice...but if something went wrong...u have to be ready.

17th Mar 2011, 14:22
172 Re “… can you get CAT IIIA approved without autoland function?”
The inference of the regulations is that a manufacturer/operator can apply for Cat 3 approval involving an auto approach and a manual landing, and apparently without the need for HUD.
The difficulty (cost) is in providing the required proof that the landings can be made without excessive workload in the visibility conditions – a lot of simulation.
Also as an alternative, it appears that a FD approach could be used, but again providing proof that ‘every’ pilot will be able achieve the required approach accuracy with the FD is another cost issue. Most manufacturers are reluctant to certificate FD Cat 2 when the aircraft already has an autopilot; there are similar cost/certification issues with HUD; it’s not as cheap as 7sr suggests. Also, a HUD has flare guidance so is this a pure manual landing? ;-)

Although CS-AWO does not deal with visibility minima per se, it is normally in EU-OPS, the AFM could have an overall a system operating limit due to the manual landing case. Thus the RVR for a manual landing would almost certainly be higher than other Cat 3 operations. The operation is still Cat 3 due to the reduced DH – the complexities/differences in ICAO definitions and practical operations.

Re the 80% auto min ht use; this may have been suspended in EU-OPS, but it is a necessary safety margin to enable a manual take over after failure at low altitude.
However, if an operation specifies autopilot disconnect at DH – say 80ft, then the 80% rule below that may be waived as the pilot would be in the loop with or without failure at 80 ft; however a good safety case is required for failures between 80 and 100ft.
I suspect that the particular subsection of CS-AWO is aimed at an operation with a DH just below 100ft.

7sr “... autolandings can be nice...but if something went wrong...u have to be ready.”
What about with HUD …. if the PF ‘goes wrong’, no HUD failure – just poor pilot performance, then who “has to be ready” and what can be done?
The autopilot – autoland failure case normally requires a GA excepting if the required visual cues are clearly seen – enabling a manual landing, but with a HUD how do you determine if the pilot part of the system has failed - impending hard landing?

17th Mar 2011, 15:31

autolandings can be nice...but if something went wrong...u have to be ready.

There is a vast difference between fail-passive and fail-active. If there are no anomalies passing alert height, fail-active is virtually assured to perform the autoland correctly. (assuming CAT III ILS and winds within limits.)

18th Mar 2011, 04:22
Thanks very much for your replies, esp. safetypee. Very informative.

Regarding CAT III ops, here is Table 7 (EU-OPS, OPS 1.430 Appendix 1 Old): http://i307.photobucket.com/albums/nn287/patrikcertain/CAT3.png

The column "Roll-out Control/Guidance system" does it refer to the automatic approach/landing system? To me the name implies it's roll-out guidance AFTER touchdown only, but that doesn't really make sense either.

Regarding CAT II ops, here is Table 6 (EU-OPS, OPS 1.430 Appendix 1 Old):

In Note 1 it specifies that for the RVR values to apply it should be auto-coupled to 80 % of applicable DH. I note though in CS-AWO 221 (Installed Equipment for CAT II), it says you need an automatic approach coupler or a flight director system. As I understand it, you can get CAT II approved without an automatic approach system as long as you've got a FD setup and it's approved. If so does the RVR values in Table 6 values still apply?

18th Mar 2011, 14:35
172 “…but that doesn't really make sense either.”
With my cynical hat on you might expect too much from the regulations, particularly harmonisation between AWO and OPS.
As you probably realise AWO looks after the equipment/safety standards, whereas OPS regulates the operation. In between there are many gaps, and where ‘unusual’ operations are approved you have to specify the context, aircraft, equipment, and/or the approving authority.
Europe may seek harmonisation in theory, but in practice … ….

My understanding of roll out guidance is that it refers to the system elements which are only used on the ground; thus it would be feasible to use a non-automatic ground roll system. One example of this was the use of para-visual displays, e.g. Trident, Tristar, and some 747s?

Re Cat 2 RVR etc. IMHO This area is a black art steeped in the mystery of pre JAR operations where operators/national authorities argued for the lowest acceptable minima irrespective of aircraft type, or to keep what they already had to be used in JAR-OPS. This was fraught with danger as each aircraft has unique attributes (e.g. glare shield cut off angle) or handing characteristics which can affect the practicality of operating in low visibility.
The European AWO regulations evolved from ECAC Doc 17. Each national authority developed their local approval systems. The UK CAA led the way on certification (Trident), and recognising operational issues, developed a reputable computer model of fog, airfield lighting, and aircraft characteristics, which provided a minimum value RVR.
This was rejected by JAA and the ensuing ‘tabular’ mess continues. JAA/EU-OPS AWO working groups have struggled (unsuccessfully) for many years to rationalise the situation, which is not aided by rigid ICAO definitions and the rapid introduction of new / novel guidance systems.
Cat 2 minima used to be what-ever the operator could argue for. More recently this has been bounded by EU-OPS tables, but there still is opportunity for variability amongst regulators in their interpretation of ‘workload’, crew skill, etc, etc, or just in understanding the rules / safety of the operation.

IMHO Cat 2 is the most risky area of AWO, in that the nature of the reduced visibility can change with altitude, fog / snow / dust. Thus having made a decision to land, this might be incorrect at a lower altitude – from experience(s).
Fortunately, the prevalence of reliable autopilots and the high cost of Cat 2 certification, most operations choose the safer auto-approach options; but now operators argue to extent Cat 2 auto systems into Cat 3 conditions – back to #1.

19th Mar 2011, 22:48
Thanks for speaking out loud what I might have expected to some degree... about harmonisation. I guess I'll just have to leave it at that :)