These days, quite understandably, as an international pax one is required to check in well in advance of the scheduled flight time. For Israel, check-in has always been about 3hrs prior to flight time. Even now, for flights to USA it is "only" 2hrs. Might it not make sense for flights to USA to require a minimum 3hr check-in so that not only can pax and their bags go through the check-in process but also the pax manifest can be approved by TSA prior to aircraft departure. The cost/expense/inconvenience of "after departure" turnbacks must be prohibitive - I am assuming airlines have to eat those costs....