A weak dollar and fear of terrorism caused the first annual drop in North Atlantic air traffic since high oil prices led to an economic squeeze in the 1970s, the airlines reported. Air traffic between Europe and North America dropped 5.9% to 19.7 million passengers last year from 21 million in 1985, according to the International Air Transport Assn. The figures are for the 48 scheduled airlines carrying passengers on the route. IATA said there were encouraging signs for the industry in 1987. Passenger totals on the route rose 4% in November and 6.7% in December, 1986, over the same two months in 1985.