Like to know how much FOD those big turbofans can absorb..
Very likely not an issue. C-17 has much bigger turbofans and does not have FOD problems operating from unpaved/austere airfields. And C-17 has shown that a turbofan in a properly designed nacelle with properly designed thrust reversers is in many ways SUPERIOR to a turbo prop in many ways. What remains unclear is if the C-390 uses C-17 style nacelles and thrust reversers.