There is growing speculation that Bombardier is close to finalizing a deal to sell more than 100 C Series planes to Delta Airlines.
The wings for the plane are made at the Canadian firm’s Belfast factory.
The Wall Street Journal, citing “people familiar with the negotiations”, reports that Delta is due to make a final decision by the end of April.
The newspaper says the deal under discussion is for 75 firm orders and options for 50 more.
The Bloomberg financial news agency has also reported that Delta and Bombardier are “nearing an agreement.”
A Bombardier spokesperson said the company did not comment on speculation “nor on the the potential discussions we may or may not be having with specific customers”.
“Bombardier Commercial Aircraft will announce material agreements if or when any are finalized,” they added.
Delta is the second biggest US airline by passenger traffic and is seeking to replace a fleet of McDonnell Douglas planes.
The order would be a major boost for the C Series programme which has suffered delays and huge cost over runs.
It has received a $1bn (£700m) bail-out from the state government in Quebec where Bombardier is based.
A deal of the reported size would make Delta by far the largest C Series customer.
Currently, the largest firm order is for 40 planes with Republic Airways, a US carrier which is involved in bankruptcy proceedings.