Looking for an incident

[Gabriel]

There it goes the clear and unambiguous procedure.

However, maybe it is a bit more clear than that, but I know if switching off a generator is the same than shedding the bus.

In the "chapter" titled "If smoke source cannot be determined and still persists", that starts with the small letter instruction you both quoted, it also reads in the step by step checklist:

AC BUS 1 can be shed as follows:
- [...]
- GEN 1 ==> OFF

AC BUS 2 can be shed as follows:
- [...]
- GEN 1 ==> ON
- [...]
- [GEN 2 ==> OFF

And in the page that follows that one it is explained how to do to shed both buses at the same time, and it includes swithing land recovery before starting the approach.

[Evan]

Originally Posted by Gabriel

There it goes the clear and unambiguous procedure.

However, maybe it is a bit more clear than that, but I know if switching off a generator is the same than shedding the bus.

In the "chapter" titled "If smoke source cannot be determined and still persists", that starts with the small letter instruction you both quoted, it also reads in the step by step checklist:

AC BUS 1 can be shed as follows:
- [...]
- GEN 1 ==> OFF

AC BUS 2 can be shed as follows:
- [...]
- GEN 1 ==> ON
- [...]
- [GEN 2 ==> OFF

And in the page that follows that one it is explained how to do to shed both buses at the same time, and it includes swithing land recovery before starting the approach.

Ah yes, I wonder if this is how they read it, your elipsis being the skipped over parts...

AFAIK, the AC busses are taken offline by either pressing the GEN 1 or GEN 2 pushbuttons on the overhead panel to off, or possibly through the ECAM.

The checklist for shedding AC BUS 2 includes this part between your [...] areas:

GEN 1 - ON

So both busses are not shed at the same time.

The part about selecting both GEN 1 and GEN 2 to OFF is the ELEC EMER CONFIG, which is not indicated UNLESS there is DETECTABLE SMOKE IN THE COCKPIT (see the boxed section) There was none in this case.

If they had read the checklist carefully, they would have had this information. But yes, the situation is not ideal for reading and this should be presented more clearly.

[MCM]

So, you notice a few things. First if all, it says to shed the AC BUS on one side—not shed both AC busses—for a reason. Secondly, it says 'if unsuccessful, [shed] the other', which implies that the opposite bus should not be shedded until it is clear that shedding the first bus did not alleviate the problem. Thirdly, it says that when it is clear that the 'the shedded side' is not involved, reconnect it, not 'a shedded side', which, taken literally, means that only one side should be shed at any given time.

1 - The "reason" could also be that you shed one first because if you shed both you would have no way of determining which side was causing the smoke.

2 - "If unsuccessful [shed] the other side"... does not necessarily imply that opposite bus should not be shed until it is clear that shedding the first bus did not alleviate the problem. That requires a "positive" confirmation. It states that if the first is unsuccessful you try the second side. That doesn't imply in any way that you then know positively that it wasn't involved, just that it hasn't totally solved the problem.

3 - The third part DOES require positive confirmation that a side is not involved. This is different to the second.

I agree with your interpretation of the checklist as the intent - but I don't see it quite as clearly as you. There shouldn't be a case of "imply" in any checklist.

I'm sure you see that there are actually a few different interpretations of this checklist that are perfectly valid, and easy to think about sitting at home. Personally this checklist is at fault for me. Talk about confusing and unclear.

[Evan]

Originally Posted by MCM

I agree with your interpretation of the checklist as the intent - but I don't see it quite as clearly as you. There shouldn't be a case of "imply" in any checklist.

I'm sure you see that there are actually a few different interpretations of this checklist that are perfectly valid, and easy to think about sitting at home. Personally this checklist is at fault for me. Talk about confusing and unclear.

MCM, I don't think you are reading my posts very clearly. I DO NOT think the checklist are clear enough and I agree that they should be clearer and less confusing. But I also see that they do instruct the pilots not to shut down both busses unless they are intending to go to ELEC EMER CONFIG, but the pilots (lacking a trained familiarity with the electrical architecture) will only understand this if they read through the entire checklist carefully, and that is probably not going to happen under this kind of stress.

It's also clear the the pilots skipped parts of the checklists, so technically I see that as pilot error, but since the checklists are poorly designed I don't necessarily blame the pilots. I do, however, think they should have been more mentally prepared and familiar with the proper procedures for shutting down busses and what the consequences would be. That's a more general issue, and the problem there probably lies in inadequate training.