Air — Civil air transport — Airliner straying off assigned international route — Airliner attacked by military aircraft — Action for damages — Liability of operators of civil aircraft to passengers — Warsaw Convention, 1929, Articles 20 and 25 — Whether operators at fault — Failure to provide adequate navigation equipment for aircraft — Risk of accidental flight over “sensitive” airspace of Soviet Union — Whether reaction of Soviet authorities foreseeable — The law of France