With the number of supertalls on the Manhattan skyline doubling within the past year, it is easy to forget about impending proposals not yet out of the ground. But now, the second supertall to result from the Midtown East rezoning is moving forward, with JPMorgan Chase filing a text amendment with City Planning for a 1,400-foot tower on the site of 270 Park Avenue. Designed by Foster + Partners Architects, the plans also come with the first renderings of the 2.4 million square foot supertall, and massing diagrams that offer a look at what’s in store for New York City’s most central business district.