Either the measurements add up or they don't. Jetblue gives you the dimensions. When you measure the bag, the length is from the top, where the handle is, to the bottom of the wheels, if there are wheels. That measurement is the same if it's lying on its side or standing up. There is no way the measurement is going to change. So....let's look at a rectangle...[__]....from side to side (or left to right) is the length, from top to bottom is the width, and the depth is the side.
When you put the bag into the overhead, it is supposed to fit, wheels in, with the handle towards the outside of the bin. That way you can reach up, take your bag down and get off the plane. It is not supposed to fit in sideways. And although a friend tells me that the wheels can be towards the outside, the FAs will tell you 'wheels in'. Now, if the overhead is narrower than some, you should try to put your bag in the overhead sideways, unless a FA tells you to put it someplace else, on the other side of the plane for instance.
But, again...measurements don't change. You measure it the same way...sideways, standing up, lying flat. The length is going to be the same, the width is going to be the same, the depth is going to be the same. It does NOT change depending on position.
I understand bringing a carry on. Everyone should do that for essentials. Are you saying that you do not have another bag that you can use as a carry on? Or, are you bringing so much that you need the bag in addition to your one checked bag? Or, are you just trying to avoid going to baggage claim? JetBlue is rather generous with the fact that they still allow each passenger to check one bag for free. Please take advantage of this and limit the size of the bag you bring on as a carry on. As PP stated, it is either within the specs or it is not. Don't play games like "if you tilt it this way" it fits. The wheels are part of the overall dimensions of the bag.
