Boeing

and Airbus are on the verge of neutralizing all the threats to their duopoly, with one exception. In the long run, a Chinese competitor could be the size needed to compete in the $ 190 billion commercial aviation market.

Boeing is in talks to buy an 80% stake in the commercial aircraft division of the Brazilian manufacturer Embraer for $ 4.2 billion. Conditions were approved last month, although the agreement still needs to be approved by the Brazilian government. New President Jair Bolsonaro sent contradictory messages Friday, telling reporters that the merger was good, while worrying about the loss of control.

Boeing's interest in Embraer is a response to the Airbus project purchase of the CSeries from 108 to 133 places– renamed A220 – from the Canadian manufacturer Bombardier. If that happens, the last deal would eliminate the last small player in the industry.

Barely five years ago, Boeing and Airbus had a fragile dominance. Bombardier and Embraer dominated the regional jet market with fewer than 100 seats, and the launch of the CSeries threatened the Boeing 737 and Airbus A319 100- to 150-seat models. It was the first real duopoly competition since the merger of Boeing and McDonnell Douglas in 1997.

At the time, investors overestimated the chances of disrupters in a market where economies of scale are paramount. Now, they may be underestimating the threat posed by the Chinese aviation industry, which is lagging behind in technology but has a scale.

Thanks to aggressive discounts, Boeing and Airbus have resulted in significant losses for Bombardier. In 2008, the Canadian company was expecting a demand for aircraft of 100 to 150 seats to cross the bar of 6,300 orders by 2027, but the CSeries only received 402 orders up to now. The Embraer E-Jet E2 series has been carefully guarded, but the margins have also distorted under pressure.

Boeing and Airbus should get more credit from investors for eliminating their competitors at a reasonable price. Taking advantage of their weight and their service abilities is the key to their domination. Just after Airbus took over the CSeries, a major airline of its kind

JetBlue

say it would buy 60 of them, and confirmed last week that he had placed a firm order. And Embraer engineers in Brazil increase Boeing's chances of designing a new, profitable aircraft.

Despite their growth difficulties, Bombardier and Embraer could have become serious challengers if they had been allowed to expand with more time and more government assistance. It should also be a telling story.

The C919, designed by Chinese Comac to compete with the A320 and 737, began flying last year. The threat seems misleading because the duopoly has better products.

However, prior to 1987, Boeing also viewed Airbus as a subsidized lower competitor. The A320 then hit the market: the state-driven growth had turned Airbus into an equal.

China's pockets are big too. According to US think tank Rand Corp, public spending on the C919 exceeds $ 7 billion. This is more than the cost of developing CSeries and a value comparable to that of the Airbus A320 once adjusted for inflation. Unlike Bombardier, Comac has a huge domestic market (the C919 already receives about 1,000 orders from Chinese airlines) and could easily expand in Asia, Russia and Africa.

Boeing and Airbus have taken the right steps. But the Chinese competition may be knocking on its doors earlier than expected.

Write to Jon Sindreu to jon.sindreu@wsj.com