Whether the question is stupid or not depends upon two things.
One, what is the position being applied for?
Two, what is the purpose of the question?

For example, if the position being applied for is one that requires immagination and creativity, and the purpose of the question is to investigate the persons ability to develop a creative answer to an absurd question, then asking how a pencil gets itself out of a blender is not a stupid question.

However, if the position being applied for is one that consists of repetative labor, such as working on a production line, then the question is stupid.

In the situation we're most likely talking about - a pilot - then there is a part of the job which does require a level of imagination and creativity, after the checklist is exhausted and there's no solution, what do you do. However in this case, it's probably better to ask a question that's along those lines "Mr. X, assuming you've exhausted the checklist and still can't get the gear down, what do you do?"

The origin of the manhole cover question, for example, came from Microsoft, and even though I have no love of Microsoft, I understand the purpose of the question completely, however I think that a candidate should be informed of the purpose of the question, so that they "talk out" their thinking process. There are some jobs, and being a computer programmer is one of them, where the problem today is completely different than the problem yesterday, so companies want to know "how" a person thinks, rather than "what" they think.