Air New Zealand studied household furniture and, in its warehouse lab, experimented with bunk beds, staggered coach seating in kind of a tic-tac-toe pattern that would allow passengers to stretch out more with legs protruding between seats, or even stacking seats atop each other in the coach cabin.

WSJ: Remedy the Squeeze in Airplanes' Coach Cabins

Yin yang seating packs in travelers more densely than herringbone and staggered designs, British Airways contends.

WSJ: The Many Ways to Catch Shut-Eye in the Sky