there was a question on another page, I think from DX Wombat, about taking off duty crew, etc. So, here a short view for those readers who aren't in the business or don't know about these things.
Off-duty crew and/or family members fly, either free or with reduced rates, as so-called "stand-by" passengers. They wait at the gate and hope that, when all regular passengers are aboard, there will be some extra seats available (sometimes due to pax not showing up, for whatever reasons). These waiting people will then, usually according to seniority or status, be alloted these free seats. If the flight is completely full, then extra jump- or crew-seats may, at the discretion of the captain, be alloted these folk. These seats are all equipped with proper seat belts so it's really no problem. Of course, the "head-count" and weight must also fit. I flew as a stand-by years ago and there were many empty seats, even though there were still stand-bys waiting that weren't allowed on. The reason: so much cargo that the weight limit had to be considered!!
I'm amazed that such a senior captain would have done this... as mentioned enough already, it was against all regulations to allow this and the risk wasn't worth it. Another point about safety: in case of an accident, no one would have expected someone in there.
The outcome of all this should be quite interesting... and more difficult in the future for stand-bys to be taken along. So again, this incident may have far reaching consequences for all.
Westy