The International Trade Commission, which is a USA government agency, voted 4-0 to reject Boeing's plea for a 300 percent duty on sales of the Bombardier jets. The panel's ruling blocks a Commerce Department decision last month to impose duties of nearly 300 percent.
"Today's decision is a victory for innovation, competition and the rule of law", Montreal-based Bombardier said in an emailed statement.
"While we disagree with the ITC's conclusion today, we will review the Commission's more detailed opinions in full as they are released in the coming days", it said.
Boeing said its business would suffer because of the C Series planes even though the ones designated for US clients would come from a new line to be built in Mobile, Alabama.
"Boeing remains confident in the facts of our case and will continue to document any harm to Boeing and our extensive US supply chain that results from illegal subsidies and dumped pricing".
How tough he talks on trade may swing markets, which became more nervous about a potential trade war after the USA imposed tariffs on imports of solar panels and washing machines, hitting Chinese and South Korean companies. The major aircraft deal set off the trade dispute with the rival USA plane maker.
After supporters poor-mouthed its chances, aircraft maker Bombardier celebrated a victory over Boeing in an worldwide trade dispute with ramifications in Alabama.
The government filing also said it would be inappropriate for the commission to make any decision about parts imported from Canada because the Department of Commerce, which controls the scope of the investigation, didn't reach a conclusion on parts.
But in a surprise ruling, the US International Trade Commission (ITC) rejected a complaint brought by Boeing.
The decision, hover, is unlikely to be the last chapter in the Bombardier-Boeing dispute.
"The decision by the International Trade Commission confirms what the United Kingdom and Canadian Governments working hand-in-hand has maintained from the outset, that this case is unjustified".
The news sent the Canadian company's stock shooting up.
The financials group, which accounts for more than one-third of the TSX's weight, slipped 0.1 percent.
Bombardier, which employs more than 4,000 people in Belfast and contributes an estimated £400m to the Northern Ireland economy, said the C-Series jets were "critical" to its operations there. Boeing contends that Bombardier's C Series competes with its own 737 Max 7, something Bombardier disputes. "We're happy to see that the ITC came to the right decision". Last year, with the plane's access to the US market in doubt, Bombardier agreed to hand control of the program to Airbus SE in exchange for the European planemaker's marketing muscle and manufacturing expertise.
In a statement, the company added: "The C-Series development and production represent thousands of jobs in the US, Canada and the UK". What's not certain is whether this is good news, or bad news, for the Port City.
The decision Friday is a significant blow to Chicago-based Boeing and gives an unexpected boost to Airbus, Boeing's rival in the commercial airline market.
Ray Conner, vice chairman of Boeing, told the commission in May that major USA airlines like Delta are among the biggest and most respected airlines in the world, which could spur other carriers to buy Bombardier planes.