CAT III Single / One engine
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NoJoke..
I was merely pointing out that having an enquiring mind (without suitable guidance) can lead you into trouble...
Approximately on the thread...
A study of FCOM 3 Abnormals and QRH reveals that for CAT 3 DUAL you need 2 engines, 2 Engine GEN, and Electrical Split. If any one of those is INOP you lose CAT 3 DUAL capability. I don't teach the "why", just the "what to do next" bit, because life's too short...
Good luck with the search..
TP
I was merely pointing out that having an enquiring mind (without suitable guidance) can lead you into trouble...
Approximately on the thread...
A study of FCOM 3 Abnormals and QRH reveals that for CAT 3 DUAL you need 2 engines, 2 Engine GEN, and Electrical Split. If any one of those is INOP you lose CAT 3 DUAL capability. I don't teach the "why", just the "what to do next" bit, because life's too short...
Good luck with the search..
TP
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TP
Thanks for that. I think the same observations were made in previous posts. When I'm instructing I do try to provide 'suitable guidance' and I find that giving the guys bare bones information (especially to the young second officers) gives them nothing to latch onto. However, if I can provide some form of logic to make a peg to hang their hats on, I find the the information sometimes sticks.
I probably have less of my life left than you, but I keep trying ~ It's never a waste of time. "Make it so"
I probably have less of my life left than you, but I keep trying ~ It's never a waste of time. "Make it so"
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matt
Hi Matt, my definition would be two independant electrical circuits (Therefore they are split). This is why I am trying to find out what gives the commonality between the APU gen and the engine gens.
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MCDHU is correct.
The reason for the limitation is the electrical supply split. Cat III dual approaches require two independent electrical sources and thats why QRH 5.04 states an electrical supply split is required for CAT III dual. When configured with single engine and an APU generator, if a fault occurs in one electrical system the other bus ties to the failed side and provides power. Therefore they are not split. When both engines are operational on a CAT III B (dual) approach they remain split even following an electrical failure on one side.
One cautionary note: following an engine failure and an APU running, the System Display (SD) ELEC page appears to show the two sides split. This is just for representational purposes and if a failure occurred on one side the tie would connect the failed side to the remaining generator.
Does that help?
The reason for the limitation is the electrical supply split. Cat III dual approaches require two independent electrical sources and thats why QRH 5.04 states an electrical supply split is required for CAT III dual. When configured with single engine and an APU generator, if a fault occurs in one electrical system the other bus ties to the failed side and provides power. Therefore they are not split. When both engines are operational on a CAT III B (dual) approach they remain split even following an electrical failure on one side.
One cautionary note: following an engine failure and an APU running, the System Display (SD) ELEC page appears to show the two sides split. This is just for representational purposes and if a failure occurred on one side the tie would connect the failed side to the remaining generator.
Does that help?
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kite
er.. I don't think so. The Bus Ties have to be open for CAT 3 DUAL capability. If a GEN fails the Bus Ties close and the a/c downgrades to CAT 3 SNGL. (If the electrical system were to remain split half the ship would be electrically dead).
If the failure happens below Alert Height (100' RA) the FMA's continue to display CAT 3 DUAL and there are no operational consequences.
It's not just representational, it's true! If you have any two GEN available AC BUS 1 and 2 are electrically split, with either one or two Bus Ties open. With only one GEN available both Bus Ties close, linking AC BUS 1 and 2.
TP
When both engines are operational on a CAT III B (dual) approach they remain split even following an electrical failure on one side.
If the failure happens below Alert Height (100' RA) the FMA's continue to display CAT 3 DUAL and there are no operational consequences.
One cautionary note: following an engine failure and an APU running, the System Display (SD) ELEC page appears to show the two sides split. This is just for representational purposes and if a failure occurred on one side the tie would connect the failed side to the remaining generator.
TP
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CAT 3 Single A-320
The reason for this is during the approach mode (only) the busses split into three and there is no closing of the bus ties. So in order to have Cat3 Dual you need two separate power supplies Gen1 and Gen2 powering each side to get Cat3 dual.The a/c maintains this condition until on the ground.
With the APU Gen whcih is alraedy running on a constant speed unit the power cannot be split to either bus separately as with for example a Boeing product.
Hope this is helpfull.
With the APU Gen whcih is alraedy running on a constant speed unit the power cannot be split to either bus separately as with for example a Boeing product.
Hope this is helpfull.
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TyroPicard, thanks for your input, but I disagree. The SD is very representational. The Single Engine + APU config, as you rightly point out, power each side, but the bus ties are still actively able and ready to transfer in case of GEN failure. This is the context of QRH 5.04 and is not considered split, even though on the SD page it looks like they're split.
There is a complex reconfiguration of electrical supply during a CAT III DUAL approach. JETZ Tech explains the nub of it. The autopilots and other essential systems for the approach must be completely independent and isolated to provide redundency. The bus ties powering these systems must be kept open. If there is a failure of one generator the autopilot and other essential systems for the approach on the failed side would be dead. The reason the failed half is not completely electrically dead is because of the unique bus configuration in CAT III Dual.
I know it could be argued why do we need to know this, but I fail to see why we as pilots shouldn't be told this. We know if it says CAT 3 SINGLE on the FMA not to do a CAT 3 DUAL, and we don't start pulling CBs willy nilly because we're told not to. My theory is that a shallow FCOM is less to do with some devilishly ingenious French philosophie but more to do with the hassle of translation. Like No Joke and many others here I'm not so good at sticking my head in the sand.
There is a complex reconfiguration of electrical supply during a CAT III DUAL approach. JETZ Tech explains the nub of it. The autopilots and other essential systems for the approach must be completely independent and isolated to provide redundency. The bus ties powering these systems must be kept open. If there is a failure of one generator the autopilot and other essential systems for the approach on the failed side would be dead. The reason the failed half is not completely electrically dead is because of the unique bus configuration in CAT III Dual.
I know it could be argued why do we need to know this, but I fail to see why we as pilots shouldn't be told this. We know if it says CAT 3 SINGLE on the FMA not to do a CAT 3 DUAL, and we don't start pulling CBs willy nilly because we're told not to. My theory is that a shallow FCOM is less to do with some devilishly ingenious French philosophie but more to do with the hassle of translation. Like No Joke and many others here I'm not so good at sticking my head in the sand.
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Guys; as I said before if you look at FCOM 1.24.10 page 2, the supply from the APU joins "downstream" of the gen line contactor for Gen 1 and as such is not an independent source of electrical power as a fault could exist between there and AC Bus 1, hence Cat 3 Single.
The A330 however, goes straight into AC1 without sharing any gen 1 circuit - and independent source of electrical power and therefore Cat 3 Dual when running with an engine generator!
The A330 however, goes straight into AC1 without sharing any gen 1 circuit - and independent source of electrical power and therefore Cat 3 Dual when running with an engine generator!
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Situations leading to CAT 3 SINGLE
So, the only time you get CAT 3 SINGLE, is when you're single-engine or have lost one of the two engine GENs.
Don't you also lose CAT 3 DUAL capability when you lose N/W STRG, with the nose gear doors open?
I am not a bus pilot, but I think I read something about this.
Don't you also lose CAT 3 DUAL capability when you lose N/W STRG, with the nose gear doors open?
I am not a bus pilot, but I think I read something about this.
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Not necessarliy - there are many failures which will downgrade you to Cat 3 single, not just an engine failure - I couldn't even begin to list them all on here!
Some are monitored by the FMGS -some are crew monitored.
Yes - you are Cat 3 single with a n/w steering failure because automatic rollout is not permitted.
Some are monitored by the FMGS -some are crew monitored.
Yes - you are Cat 3 single with a n/w steering failure because automatic rollout is not permitted.
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Ipaq, you are right.
CAT III dual means, that your systems are fail/operational, that is in case of a failure, you can continue after getting the click,click,click, and CAT III single means, you get the warning and have to abort. The system is fail/safe. The reasons for it are legion, Elec, Hydr, steerability, autopilot, IRS, just check the table...
Nic
CAT III dual means, that your systems are fail/operational, that is in case of a failure, you can continue after getting the click,click,click, and CAT III single means, you get the warning and have to abort. The system is fail/safe. The reasons for it are legion, Elec, Hydr, steerability, autopilot, IRS, just check the table...
Nic
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According to Airbus, for A320.
The power supply split function that monitors the electrical segregation of the FMGC's does not consider the APU generator as an independent electrical source. As a consequence, when an engine generator is lost the capability is downgraded to CAT 3 Single.
The electrical power supply split function monitors......
-The two BUS TIE contactors
-The DC TIE contactor (between DC BUS 2 and DC BAT BUS)
When one of the above contactors is closed, the FMGC considers that the power supply split is lost (independently of the APU generator)
The A330 does not have this restriction and can be CAT 3 Dual capable even with one engine generator failure as APU is considered an independent electrical source.
Don't know why this isn't in the A320 fcom's.
Scally
The power supply split function that monitors the electrical segregation of the FMGC's does not consider the APU generator as an independent electrical source. As a consequence, when an engine generator is lost the capability is downgraded to CAT 3 Single.
The electrical power supply split function monitors......
-The two BUS TIE contactors
-The DC TIE contactor (between DC BUS 2 and DC BAT BUS)
When one of the above contactors is closed, the FMGC considers that the power supply split is lost (independently of the APU generator)
The A330 does not have this restriction and can be CAT 3 Dual capable even with one engine generator failure as APU is considered an independent electrical source.
Don't know why this isn't in the A320 fcom's.
Scally
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Confusion reigns..
kite
JETZtech's nub..
There seems to be a fair bit of confusion here. The electrical system does not behave differently just because CAT 3 DUAL is displayed on your FMA. In normal operation the AC BUS ties are both open; so is the DC TIE between DC BAT BUS and DC BUS 2. None of this changes on the approach, there is no "complex reconfiguration", no "unique bus configuration". The normal configuration ensures an electrical split (AC and DC) between FMGC 1 and 2.
In the event of a GEN failure the AC BUS ties close and the remaining GEN powers the whole system. You hear a triple click and see CAT 3 SNGL annunciated, because the FMGC's are no longer electrically split. You will also get an ECAM warning above 800 ft.
It is that simple, and the important reaction is operational rather than technical. Why delve deeply when you don't even understand the basics?
As to why the APU GEN is not considered an independent electrical source .. I haven't a clue! Airbus have decided, and because their decision works in a safe direction I am not going to question it. Not sticking head in sand, just practical aviation.
Hope that helps - but if not, print out your posts and mine and take them along to your friendly neighbourhood TRE and ask his/her opinion.
TP
There is a complex reconfiguration of electrical supply during a CAT III DUAL approach. JETZ Tech explains the nub of it. The autopilots and other essential systems for the approach must be completely independent and isolated to provide redundency. The bus ties powering these systems must be kept open. If there is a failure of one generator the autopilot and other essential systems for the approach on the failed side would be dead. The reason the failed half is not completely electrically dead is because of the unique bus configuration in CAT III Dual.
The reason for this is during the approach mode (only) the busses split into three and there is no closing of the bus ties. So in order to have Cat3 Dual you need two separate power supplies Gen1 and Gen2 powering each side to get Cat3 dual.The a/c maintains this condition until on the ground.
In the event of a GEN failure the AC BUS ties close and the remaining GEN powers the whole system. You hear a triple click and see CAT 3 SNGL annunciated, because the FMGC's are no longer electrically split. You will also get an ECAM warning above 800 ft.
It is that simple, and the important reaction is operational rather than technical. Why delve deeply when you don't even understand the basics?
As to why the APU GEN is not considered an independent electrical source .. I haven't a clue! Airbus have decided, and because their decision works in a safe direction I am not going to question it. Not sticking head in sand, just practical aviation.
Hope that helps - but if not, print out your posts and mine and take them along to your friendly neighbourhood TRE and ask his/her opinion.
TP
