Bit disappointed with the replies to my post. In the first place SetStandard obviously completely misunderstood me. In the case of other responses, yes, I'm old and did work for a bank for a short while (amongst other things) but that doesn't make me totally stupid or unwilling to learn. I explained that I was a fairly ignorant MOP rather than a fully trained pilot and was asking why, during a long period of auto pilot ...IF.... there was nothing to do for a long time, it would be a problem for a pilot to take a short nap given the many audible warnings available (and could be made more available) should there be a problem. We are told how modern airliners have every safety feature available and it would be worrying if we thought that, despite these features, it needs a pilot to monitor every single second of a flight. It would be nice to be given a reasonable answer rather than insults.