A widening split in the global aviation industry over a proposed carbon tax may trigger a trade war, the chief executive of plane manufacturer Airbus said Monday. \"I have to say I\'m really worried also as a manufacturer about the consequences,\" Airbus Chief Executive Thomas Enders told a conference on the eve of the Singapore Airshow. \"I have seen the position in China, in Russia, in the US, in India, and what started as a scheme to present a solution for the environment has become a source of potential trade conflict,\" he added.