Not so simple or obvious in a free market, or a free society that doesn't depend on big daddy government for protection from everything. Private airlines will be incentivized to keep their planes safe. How many customers, jets, and employees do they want to lose to terrorists? How many CAN they lose before they are out of business? The winners will be those airlines that can keep their planes safe and do it politely and cheaply. I trust the free market can do that; we already know governments cannot.