Viggen, Riding the jumpseat in the US is a bit different than in Europe. At UA to ride in the cockpit you MUST have checked in at the gate with a company ID of an airline that UA has a jumpseat agreement with. If you are non UA pilot I beleive you must be in uniform as well. In either case - the poster was correct who stated that 99.9% of the time if there is a seat in the cabin the jumpseater sits there for takeoff/duration of the flight. Both airlines have released which seats the hijackers were issued boarding cards for.