An accumulation of ice in the fuel system, which formed from the water normally present in jet fuel during commonly encountered flight conditions, which accreted and released, restricting the fuel flow at the right engine fuel-oil heat exchanger inlet face. Contributing to the incident were certification requirements (with which the aircraft and engine fuel systems were in compliance), which did not account for the possibility of ice accumulating and subsequently releasing in the aircraft and engine fuel feed system upstream of the fuel-oil heat exchanger.