Atlanta - Delta Air Lines is defending the partnership between Airbus and Bombardier in the C Series by urging Washington to reject certain allegations raised by Boeing in the dispute with the aircraft manufacturer in Quebec.

In a document filed this week with the Commerce Department, the American airline operator responds to recent criticism from the Boeing regarding the project to assemble the Bombardier's C family aircraft in the United States.

Airbus and Bombardier believe that an assembly line will allow the C Series to escape the punitive measures by Washington if some parts manufactured in the United States.

Boeing has already questioned the appropriateness of building a new C Series assembly line at Airbus facilities in Mobile, Alabama, claiming that the idea would not have arisen without the imposition of preliminary punitive measures.

"Boeing took the opportunity to attack Delta, opposing the creation of new jobs in the manufacturing sector and new investment," said the Atlanta based airline.

Airbus and Bombardier believe that an assembly line will allow the C Series to escape the punitive measures by Washington if some parts manufactured in the United States.

Delta, which placed a firm order for 75 CS100 aircraft in 2016 with options for an additional 50 aircraft, appears to be opening the door to the possibility of postponing the first scheduled deliveries in the spring of 2018 to have its aircraft assembled in the Airbus facilities in the US.

"The Commerce Department only needs to analyze Boeing's supply chain to see that there is an economic justification for an assembly line in the United States," Delta writes.

The carrier points out that for its family of 787 aircraft, Boeing does business with many foreign suppliers, some of which are in China and Japan, for the manufacture of certain components.

In its spring complaint, Boeing accused Bombardier of receiving significant financial support to offer "ridiculous" prices to the US carrier in order to win a large order.

Delta has always claimed that the American manufacturer had never been at the bargaining table for this contract.

The American aircraft manufacturer is, therefore, questioning the injection of 1 billion US dollars by the Quebec government.

In recent weeks, Bombardier, Delta, Quebec City, Ottawa, the European Commission and the Caisse de dépôt et placement du Québec (CDPQ) have all criticized Commerce's approach to its investigation.

The Commerce Department is expected to make its final decision in about a month and the US International Trade Commission (ITC) will have to determine early in 2018 whether Bombardier's practices have actually hurt Boeing.

During the week, Boeing also submitted other arguments to the Commerce Department, noting that no private investor was present for the C Series in 2015 when the program was undergoing significant turbulence.

The American aircraft manufacturer is, therefore, questioning the injection of 1 billion US dollars by the Quebec government for a 49.5% stake in this program, suggesting that this sum constitutes a subsidy.

Marked by delays and cost overruns, the C Series program, which weighed heavily on Bombardier's finances, was a big risk, says Boeing. According to the company, the respondents simply were not able to provide Washington with examples of private investors.

With the latest agreement between Airbus and Bombardier, the European manufacturer will hold 50.1% of the partnership in C Series without paying a single penny. Bombardier's share will fall to 31%, while that of the Québec government is expected to fall to around 19%.