Wont you want to do that silently?
Won't it be strange seeing 100s of people around speaking on their phone at loud noises talking to the search engine? Won't you would want to do things without disturbing others. The noise people make during these voice searches are painful to the people around that place. How are we planning to manage that? Isn't this a bad social etiquette? And this is not only about flight but in general. Won't the voice support create trouble to the people around. You are sitting in your cubicle at office and one voice engine wants you to say out loud something. Gosh, that's bad, really bad.