The world's largest plane, Stratolaunch, has a completed a key taxi test ahead of taking to the skies for the first time. The gigantic plane, which is the vision of late Microsoft co-founder Paul Allen, is believed to be close to its first flight after reaching a record-breaking 90mph during medium-speed taxi testing at the Mojave Air & Space Port. Allen died Monday in Seattle from complications of non-Hodgkin's lymphoma, aged 65. The massive plane has a wingspan longer than a football field and comes equipped with two cockpits, 28 wheels and six engines normally used to power 747 jumbo jets. Eventually it will be used to transport rockets carrying satellites and even a newly revealed manned space plane into the Earth's upper atmosphere, where they will blast off into space.