CAT IIIA/B in B737 NG

[KrazyKraut]

Hi there,

anyone out there who operates the B737 to CATIIIB?

I am interested to find out:


What are the equipment requirements for dispatching, specific to CATIIIB

What are the equipment requirements once airborne to commence a CATIIIB approach?

In terms of required equipment, how does CATIIIA differ from CATIIIB?


Thanks for any responses!

[ABBOT]

737 NG can operate to CAT 111A using dual autopilots to achieve auto land. The 737 has no autopilot rudder channel, hence no centreline guidance after landing. HGS equipped aircraft can achieve CAT 111B by use of the HGS to maintain the centreline after landing.

[Denti]

Quite wrong of course. The 737NG can be ordered with a rudder actuator, the rudder channel is part of the Rockwell Collins auto flight system. With the actuator fail operational auto land and automatic rollout is possible to no decision height and 75m rvr, in fail passive mode a reduced rvr can be used as automatic rollout is still available, we use 125m 75m 75 in LAND2 or CAT III OEI. There is no requirement for a HUD in this case, a HUD is simply another possibility.

[alf5071h]

The information required should be within the regulations and guidance materials below;
http://www.skybrary.aero/bookshelf/books/2092.pdf
http://www.skybrary.aero/bookshelf/books/2119.pdf

You will also need to refer to CS AWO.
http://easa.europa.eu/system/files/dfu/decision_ED_2003_06_RM.pdf

[Denti]

1) It is basically the same as for CAT IIIa, main difference is that three IRS are needed, of which one can be the ISFD. Of course the aircraft has to be CAT IIIb capable to begin with.
2) Same as for CAT IIIa, again with the difference that three attitude sources are needed instead of two and that both engines are running (single engine downgrades the system to CAT IIIa). It is checked by pressing the C/R button on the MFD panel (allows switching to secondary engine instruments or hydraulic/flight control pages on the lower DU, has a third button on fail operational planes) which generates a RECALL message on the upper DU or a corresponding autoland system downgrade message (NO LAND3, NO AUTOLAND).
3) As mentioned, the rudder servo is needed and the Rockwell Collins MCP/Autoflight system and of course a working ISFD, which is, if installed a mandatory equipment item anyway.

I do not know how it works in the HGS world as we only operate the CAT IIIb autoland capable planes.

[KrazyKraut]

Thanks for the meaningful answers, guys (especially Denti).

Denti, other than what you have written, are there any other operational differences between CAT IIIA and CAT IIIB?

For instance, is auto-rollout mandatory?

[Denti]

As far as I know it is mandatory if no HUD/HGS is installed. The autopilot and with that the automatic rollout can be disconnected if the required visual segment can be kept on the ground. However it is an integral part of the auto land system and can not be deselected apart from the rest of the auto land system. Leads to the interesting display of two different armed lateral modes during approach, LNAV and ROLLOUT.

On a fail operational 737NG auto rollout will be always become active if both autopilots are engaged and below roughly 1500' AGL. We can do auto lands in CAT I conditions if we like, and in that case auto rollout will still be active. Kinda dangerous without protected areas as you cannot over pressure the autopilot on the rudder pedals if you get a localizer deflection on the ground.

Here a picture that is somewhat unusual as all auto land modes are active, but there is still a NO AUTOLAND warning active, had it on one of my last flights on the NG.

https://lh3.googleusercontent.com/-AuYPVtWzObw/VBXWfdLoWTI/AAAAAAAABYE/aOsUlAz__BY/s640/image.jpg

[KrazyKraut]

Denti, thanks again for your help.

That is an interesting picture indeed. In our B737 FCOM (Ch. 4, "fail-operational autoland status annunciations", it clearly states "Flare and Rollout will not arm with NO AUTOLAND annunciated".

Do you have any explanation for this?

[Denti]

I have to correct myself there, it was indeed a picture taken during my last month on the NG, however in a surprise simulator visit and it is simply a simulator failure. Quite an old simulator that had to be modified to simulate our fleet configuration (CAT IIIb and all the other new stuff) which alone took around 2 years and still has some glitches.

[KrazyKraut]

Thanks Denti. That makes me feel a bit better... ;-)