Plane manufacturer Airbus has applied to patent mezzanine aeroplane seating that would stack passengers on top of one another.
According to the document – filed by the aeronautics giant's Hamburg headquarters and published by the European Patent Office – the seating would comprise "at least one first seat arranged at a first lower level, and at least one second seat arranged at a second elevated level".
The extra mezzanine level of seating could be installed down the central section of the plane, to take advantage of what the Airbus patent refers to as "a substantially unused upper lobe of the aircraft fuselage".
Diagrams show the upper level being accessed by stairs or ladders attached to the side of the seating.
Both levels of seats would be capable of being reclined, and the patent document includes drawings that demonstrate various possibilities for fitting fully horizontal seats into the available space without compromising on lower level passengers' headroom.
Other illustrations show alternative arrangements of seating, including one where the upper level of passengers could face the opposite way to the passengers beneath.
Although the design has been proposed for an aeroplane, the patent also suggests that it could apply to other modes of transport such as buses and trains.
Airbus told British newspaper The Telegraph that the patent is just one of several hundred filed each year, and there was no guarantee it would be adopted into existing aircraft designs.
It's not the first patent for unusual seating filed by the plane manufacturer: diagrams of chairs that would substitute seat cushions for bicycle-style saddles emerged in 2014.
A more luxurious proposal from Airbus involved a conceptual aeroplane with a transparent cabin and virtual golf course, which would offer passengers shape-shifting seats, aromatherapy and antioxidant-enriched air.
To coincide with the London 2012 Paralympics, transport design studio Priestmangoode created a conceptual airline seat with a detachable wheelchair that clipped back into a fixed seat frame when required as a normal aisle seat.