According to a report published on telegraph.co.uk, aircraft manufacturer Airbus has designed a mezzanine level for planes which would stack passengers above others. However, it is questionable, that the invention will ever make it past the design stage. To read the article which also contains sketches of the mezzanine level seating, see http://www.telegraph.co.uk/travel/travelnews/11914067/Airbus-designs-mezzanine-to-seat-plane-passengers-on-top-of-each-other.html
