Nonetheless, there’s circumstantial evidence to support suspicions that quality and price may not be the only factors affecting the choice of Boeing’s Japanese partners. Japan’s market for commercial aircraft is dominated by Boeing to a degree unrivaled by any other country. Over the last decade, Boeing supplied over 80 percent of the aircraft ordered by Japanese customers. The nation’s flagship airline, Japan Airlines, has never ordered a plane from Airbus, Boeing’s rival. The Japanese carrier All Nippon Airways flew the 787’s maiden commercial flight and has placed an initial order for 50 aircraft. Boeing said that over the last 50 years, Japanese carriers had ordered 900 Boeing aircraft, making Japan one of its top markets by dollar volume.

Airbus has struggled to gain traction in the Japanese market. Evidently taking a page from the Boeing playbook, it said it invested an estimated $4.6 billion with Japanese suppliers for its jumbo A380. But $4.6 billion is a drop in the bucket compared with Boeing’s spending over the decades. Airbus has since booked four orders for the A380 from the low-cost Japanese carrier Skymark Airlines. Airbus has long accused the Japanese government of engaging in improper subsidies to Boeing; an Airbus executive called the 787 the most heavily subsidized civil aircraft in history.

China hasn’t signed the Agreement on Trade in Civil Aircraft, and aviation analysts have been watching closely to see if it will follow Japan’s lead or embrace a free trade approach. Airbus has invested more heavily than Boeing in China, where Airbus built its first assembly line outside of Europe. But so far, its market share in the rapidly growing Chinese market has remained about the same as Boeing’s. China is also trying to develop its own domestic aircraft industry to compete with Boeing and Airbus.

Boeing patronage has certainly brought benefits to Japan. Its three giant “heavy” industries — Mitsubishi, Kawasaki and Fuji — have been significant partners with Boeing since the development of the 767. According to Boeing, they supply major components of the 767 and 777 airframes and were closely involved in the 777’s design. The company said its Japanese partners designed and developed 35 percent of the 787 airframe structure, including the main wing box, which is the first time Boeing has ever entrusted such a critical design component to another company. Under their agreements with Boeing, they produce components almost exclusively for Boeing. Mitsubishi is now manufacturing its own regional jet thanks in part to what it learned from working with Boeing.

Boeing said that more than 65 Japanese companies were suppliers for both commercial and military products. Boeing said it directly or indirectly employed 22,000 people in Japan, or 42 percent of the country’s aerospace work force. Boeing also has close ties to Japan’s Defense Ministry, and the company said the two had “a long history of working together to meet Japan’s defense needs.”