Bombardier has already made "significant" progress towards opening an Alabama CSeries final assembly site that will closely resemble the company's Mirabel assembly facility.
"Bombardier… is moving ahead posthaste, obtaining regulatory approvals, conducting site visits and planning, consistent with antitrust law, for the operation of the US [final assembly site]," says a 17 January document filed with the US International Trade Commission (ITC).
The company has made "significant further progress toward construction of the US" site since 27 December, adds the document, signed by an attorney with Covington & Burling, a law firm representing Bombardier.
The filing comes in response to a request for more information about Bombardier's Alabama plan from the ITC, which is in the final stages of its CSeries trade dispute investigation.
Boeing also submitted a document to the ITC providing more information about its recent merger discussions with Brazilian manufacturer Embraer. The ITC had likewise requested more information from Boeing.
The publicly available versions of both documents were heavily redacted and contained few details.
"Planning of the US [assembly line] is now at an advanced stage, with nearly every aspect of the US [line] having been planned in detail," says Bombardier's filing.
Bombardier has identified tooling and other equipment required for the new site, and has prepared a human resources plan for staffing the US operation, which will eventually create 400-500 on-site jobs, the filing says.
CSeries vice-president Rob Dewar told the ITC in December that the planned site in Mobile, Alabama will be an "exact replica" of the company's production process in Mirabel, it adds.
Boeing's filing contains even fewer details.
It insists that, unlike the CSeries, Embraer's regional jets do not compete with Boeing 737s.
"CSeries directly competes today, and will directly compete tomorrow, with the 737-700 and the 737 Max 7 in the 100- to 150-seat [large commercial aircraft] market, while Embraer's regional jets simply do not and will not," Boeing's filing says.
Boeing also attached media clippings showing it has collaborated with Embraer on some projects in the past.
The ITC is set to rule on 25 January on whether Bombardier's 2016 sale of CS100s to Delta Air Lines harmed Boeing. If the commission does find harm, imported CS100s will be subject to import duties already set by the US Department of Commerce at 292%.
The Commerce Department will not impose the duties if the ITC finds no harm.