The VC-25As are to be replaced as the cost of maintaining the aging systems on their 30-year-old airframes and less efficient GE-CF6 engines has begun to surpass the cost of acquiring a new aircraft.[56] On 28 January 2015, the Air Force announced that the Boeing 747-8 would be the next presidential aircraft.[57][58] On 6 December 2016, President-elect Donald Trump tweeted his opposition to the Air Force One replacement because of its high cost, "more than $4 billion".