But the four-member commission ruled unanimously that "100- to 150-seat large civil aircraft from Canada do not injure USA industry".
In a surprise decision, the US International Trade Commission (ITC) ruled in favour of Bombardier over American firm Boeing, which claimed its rival received unfair state subsidies from the United Kingdom and Canada.
In an unexpected choice, the U.S. Global Trade Commission has ruled against aviation goliath Boeing in an unpleasant exchange body of evidence it brought against Bombardier over traveler streams its Canadian opponent sold to Delta Air Lines.
Boeing, the American giant that is the world's largest aerospace company, accused Bombardier, a smaller Canadian rival, previous year of accepting illegal government subsidies from Canada and Britain for its C Series programme, allowing it to sell the jets cheaply in the United States. The Canadian government followed a year ago with a C$372.5 million ($300 million) financing package for two Bombardier jet programs, including the C Series.
Typically, domestic industries seeking relief under these statutes (the U.S. Antidumping and Countervailing Duty laws) are successful because the evidentiary thresholds are so low.
"Whether you're sympathetic to Boeing or not, you have to admire the process", he said.
Chicago-based Boeing says it is disappointed by the decision and will review the commission's detailed opinions when they are released in the coming days.
The trade dispute has spilled over to Boeing's customers. The case threatened to raise tensions between Washington and USA allies Canada and Britain, which has a Bombardier plant.
British Prime Minister Theresa May tweeted that she welcomed the ruling.
The ITC vote contrasts with President Donald Trump's decision this week to slap tariffs on solar panels and imported washing machines on the grounds that they're harming US industry. The Trump Administration's Commerce Department had proposed 300-percent duties on Bombardier sales in the USA, primarily to Delta Airlines.
Boeing needed just two of the four ITC commissioners to vote its way to win, while Bombardier needed three.
The case report will be made available March 2 on the ITC website.
The case before the ITC had also risked heightening trade tensions between the United States and the UK.
The ITC's role is to determine whether the aircraft manufacture industry in the U.S. is damaged by imports that the administration believes are being sold too cheaply.
Bombardier shares jumped more than 15% after the ruling.
The dispute took a twist in mid-October when Bombardier agreed to sell the C Series plane to Airbus, a deep-pocketed European aerospace giant that is Boeing's closest competitor.
Yet as Bombardier and Embraer extend the size of their flagship regional airliners, they have closed the gap with Boeing's 737 and Airbus's A320 models.
But the case, centred on a complaint by aerospace rival Boeing, was dismissed.
"It is supposed to be an independent tribunal that looks at the facts and that's what I would argue they've done", he said.
"It's been a hard standard over time", he said.
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