An aerospace analyst concludes that Boeing Co. last year sold its planes at below cost, with average prices ranging from 14% to 27% below list prices. Paul Nisbet, an analyst for JSA Research, tried to quantify Boeing's practice of discounting in its price war with Europe's Airbus Industrie. Using figures disclosed by Seattle-based Boeing, Nisbet said customers paid $31.5 billion for the 559 planes Boeing delivered in 1998. He then calculated average actual prices paid per aircraft model and compared them with list prices. Boeing officials declined comment on Nisbet's report. Boeing, the world's largest maker of commercial jets, made $1.12 billion in profit last year on $56 billion in sales. But Nisbet said Boeing "was $590 million in the hole" on aircraft sales alone. Boeing shares closed up 94 cents at $34.88 on the New York Stock Exchange.