China’s flagship civilian aircraft maker is planning to upgrade the cabin capacity of its C919 narrowbody airliner to improve passenger experience and boost the plane’s chances of challenging the Boeing-Airbus duopoly, a source with knowledge of the plans said. Bigger overhead luggage compartments and drip-proof air conditioning outlets are among the design upgrades being sketched out by the Commercial Aircraft Corporation of China (Comac). “Comac has realised it must make passengers as...