United Airlines is set to buy 150 Boeing 737s to replace its older planes that are not fuel efficient. The order was placed Thursday that includes 100 Boeing 737 Max 9. It is a new version of the airplane that has new engines and other improvements to cut its fuel consumption. The planes will be delivered to United Airlines in 2018. United Airlines is also purchasing 50 Boeing 737-900ER. The planes will arrive late next year. United Airlines’ order doesn’t mean that the company is getting bigger....