"History has shown the manufacturer with the biggest twin-engine jetliner wins"

This is the conclusion by Richard Aboulafia -vice president at aerospace consultancy Teal Group- when talking about the bigger and bigger aircraft that are currently under development by both Boeing and Airbus.

Photo by @LH526 at airliners.net

In the historically boom-and-bust global airline industry, it is mostly boom times again. After a withering global economic crisis, tourists and businesspeople are again traveling. Rising airline profits are fueling demand not just for more jets, but for larger models that only Airbus and Boeing can build—and which are more profitable for the plane makers.

Photo by @LH526 at airliners.net

"The average size of aircraft has been moving up. Every year it gets slightly larger," said John Leahy, chief salesman for Airbus's commercial-plane unit. In profitable times like these, carriers are drawn to larger jets to carry more passengers without having to add flights.

Though bigger planes cost more to buy, airlines can spread costs across more passengers by adding seats, often without requiring much extra staff.

Photo by Sascha K @knig_s

Both manufacturers have begun to adapt their production plans and even their jets to reflect the shifting market.

Over the next 20 years, Boeing estimates the average twin-aisle, or widebody, jetliner will grow by about 20 seats.

In Airbus A350 XWB family, interest has fizzled in the smaller A350-800.

http://nurhakhan.com/2014/07/25/a350/

The bigger jets bring design challenges. Airbus is adding extra landing-gear wheels and upgraded the engine design for the bigger A350 model, which is expected to be delivered in 2017. Boeing, meanwhile, will fit folding wingtips to its planned bigger 777X to allow the jet to use the same gates as smaller planes.

https://www.flickr.com/photos/thomasbecker/14556720298/

Is the extra effort worth it?  Up to a point. While bigger is generally better, airlines tend to favor twin-engine jets over more costly and even bigger four-engine models.

Airlines worry they can't profitability fill planes that seat more than 450 passengers. If travel demand weakens, airlines tend to hedge with smaller jets to maintain frequencies at lower capacity.

Photo by Olli B. @oller_o

While carriers in much of the world are enjoying the good times again, there are early warning signs too many big jets have come into the market. Deutsche Lufthansa and Air France-KLM in recent weeks issued profit warnings as capacity on intercontinental routes has outpaced demand.

"It goes in swings and roundabouts," AerCap's Mr. Kelly said.

Based on the article “Plane Makers' Sweet Spot: Bigger, but Not Too Big” published in The Wall Street Journal.