CAT III Single / One engine
 

When on one engine we get CAT III Single on the FMA. I am sure I have read that for CAT III Dual we need two engine generators but I can't find the reference. Is the the requirement for two engine generators to ensure the electrical split, and if so, what is the difference between two engine generators and lets say one engine gen plus the APU gen? Sorry should have mentioned the A320 family!

Cat III
 

Yes I think I've that bit about eng gens. Will post when I find it.

M.T.

The electrical requirement for Cat 3 Dual is 2 independant electrical systems which the 2 eng gens give you, but with an eng gen and the apu gen, there is apparently a common relay somewhere in the system and thus that electrical configuration only qualifies for cat 3 single.

mcdhu

I'm flying CAT III single engine with ERJ145 (HGS) and have 2 generators per engine.
I never been told about this requirement before !
this piece of info could maybe help you a bit !
mupepe

On the CRJ -700/900 you can go CAT3 with HGS and one engine inop.
APU generator has the same capability as the engine driven one,so you are safe here.

Regards,
CptRegionalJet:ok:

Flying ERJ or CRJ CAT III by hand on the HGS has nothing to do whatsoever, one or two engines on, with the indication Cat III single/dual on an A320 !!!

The Airbus indication has to do with the Autopilot being fail/operational or fail/passive, as there is no autopilot doing CAT III for you on the ERJ CRJ the two don't compare...

Nic

CRJ
 

The APU gen is the same as the Eng gens on the bus 90 KVA but I think it the problem that mchdu points out that brings us down to CAT III single. All the wiggley amps go into the same box and spoil the show. Still can find a reference.

Pretty sure the Cat 3 Single limitation when eng out is more related to HYD redundancy.

Ie You need all 3 HYD systems to be be Cat 3 dual.

Thats why on 343/5 if you loose eng 1 or 4 you can be CAT 3 dual,(as you still have 3 sys) but eng 2 or 3 you only be Cat 3 single.

:)

We don't use AI FCOMs rather customized company Manuals, so I don't know where it's hidden in the original FCOM.

But we have the following table in OM-B -> Normal Procedures -> Supplementary Procedures -> LVO -> Airborne Equipment required for CAT II/III Approach

and there it says 'Engine Generator - Number required for CAT III Dual: 2'

Rgds MAX

Max - the table you refer to is in the Airbus QRH 5.04, but no explanation apart from the title of that line which is 'Elecrical Supply Split'. I'll keep looking!

cheers,
mcdhu

Redundancy
 

The original question, for A-320, states that the Autoland status is Cat3 Single for a single engine approach, then questions whether that has to do with one of the electrical sources being the APU generator instead of the generator of the broken engine.
No, the status is Cat3 Single because you have only 1 engine operating!

Cat3 Dual means the system is fail operational: no single failure (from that start situation) will preclude the system from completing the landing automatically.
Note: if that single failure occurs below Alert Height. If the failure happens above Alert height, you will see a reversion of Autoland status to Cat3 Single.

If you start the approach with already one engine out, then how can you expect the system to cope with a failure of the remaining engine? Thus when flying single engine, the system is not fail operational, but fail passive.
The misleading concept may be the point that in this Autoland status discussion, the failure of the second engine would be a “single failure”, because you have to look at the situation with which you started the approach, namely with one engine already out – from that initial situation, a “dual engine failure situation” is only one step away, so only “a single failure”.

Now, for a 2 engines operating situation, but with 1 engine driven generator u/s and replaced by the APU generator – indeed, there you will also see Cat3 Single, according to FCOM. The reason for that, not sure,like MCDHU stated earlier, there may be some common relay in the system.

NoJoke
Do you really need to know the reason? Can you not just accept that the Autoland status of the a/c is as displayed and make operational decisions accordingly?
i.e keep it simple
TP

APU GEN has no CSD
 

My best guess is that the APU GEN has no constant speed drive like the two engine generators.

My company asked Airbus some time ago if they recommend to start the APU before commencing a low visibility approach (it has been a common practise by commanders who flew the MD before)
The answer was more or less: "as you like but there is no need for it and doing so doesn't improve your chances against a downgrading because the APU GEN has no constant speed drive."

W.

TP
 

I suppose you could say that about anything. I apologise for having an enquiring mind. I see from your profile you are an SFI on the bus, good luck with your students. :cool:

Cat III Dual Req'd Equipment
 

In the QRH 5.04 a note at the bottom of the page states; 'Electrical Power Supply Split: this ensures that each FMGC is powered by an independent electrical source (AC and DC).'

But no mention of ENGINE or APU.

The information we had once from our tech. guys is that the APU generator shares the same circuitry to AC Bus 1 as the engine generator, therefore is not considered a completely seperate source of AC power, unlike the A330which is totally independant.

APU's always run at the same speed (100%) unlike the engines which run at variable speeds therefore there is no need for a csd on an apu generator.

Enquiring minds read on...

Many years ago some enquiring minds pulled a CB on a fully serviceable DC-10 to see if that piece of kit was involved in controlling N1 ... it was involved.. one of the engines oversped, and a fan blade detached, punctured the fuselage and killed a passenger who was quietly enjoying the view from his window seat.

Like I said, keep it simple.
TP

I'm aware of this - but still this is my best guess why you don't get CAT III DUAL if SE+APU GEN running.
The electrical supply of the relevant AC busses is assured as well, but something has to be different!

TP
 

What? :rolleyes: Back to the thread ..... :oh: