In-flight entertainment (IFE) is a hit-or-miss feature for airlines. There are constraints on what features planes, particularly older ones, can support, and many airlines don't want to invest much in IFE, which means that passengers can have very inconsistent experiences with IFE from airline to airline.

But now some airlines are bypassing the cost and space limitations of legacy IFE systems and going with a much more consumer-oriented option. Singapore Airlines subsidiary Scoot is one of a handful of airlines that have recently started renting iPads to economy passengers for US$17.65 per flight, pre-loaded with 50 GB of movies, TV episodes, games, and music. (They're free to business-class customers.)

Giving every passenger an iPad may seem rather excessive, even with the nominal rental fee, but do the math in terms of an airline's most precious factor -- weight -- and it starts to makes sense. Scoot operates 402-passenger Boeing 777s. Typically IFEs weigh about 13 pounds, which includes equipment in the seat back and underneath the seat. Swapping iPads for these on-board systems would save 4,647 pounds or 2.3 tons, per flight, assuming a full plane.

That's a lot of weight -- and a lot of fuel -- saved. Plus, the airline gets the benefit of happier customers who get a chance to while away the miles in the air doing something they want to do, with far more choices.

Back in the terminal, smartphones are already stepping up to ease the trip. Many airlines have implemented mobile boarding passes, which are emails or custom web pages sent to flyers' phones that display the boarding information and confirmation codes for that passenger, usually shown as a QR Code.