• Alaska Airlines and Hawaiian Airlines will still need approval from the Transportation Department to complete the deal
• The Justice Department's period to complete its investigation into the deal expired Tuesday without a lawsuit seeking to block the deal.

Alaska Airlines said its plan to acquire Hawaiian Airlines has cleared the U.S. Justice Department after the period for antitrust regulators to finish an investigation of the deal ended without a lawsuit to block the transaction, eight months after the two carriers announced a $1.9 billion agreement to combine.

The two airlines now have to win approval from the U.S. Transportation Department before the deal closes. It wasn't immediately clear how long that process will take.

The combination would become the biggest U.S. airline merger since Alaska combined with Virgin America in 2016, according to Mergermarket.

"The time period for the U.S. Department of Justice to complete its regulatory investigation of the proposed combination of Alaska Airlines and Hawaiian Airlines under the [Hart-Scott-Rodino Antitrust Improvements] Act has expired," Alaska Airlines said in a statement. "This is a significant milestone in the process to join our airlines."

The development comes after the DOJ won a court ruling in January that blocked JetBlue Airways' acquisition of Spirit Airlines. Last year, the DOJ won another suit that undid a partnership in the Northeast between JetBlue and American Airlines.

Hawaiian had faced a host of challenges in the months leading up to the deal — which the two carriers announced last December — including the Maui wildfires, increased competition from Southwest Airlines, and the slower recovery of travel to and from Asia after the Covid-19 pandemic.

Hawaiian has posted net losses in all but one quarter since the start of 2020, but executives have recently said booking trends are improving. Hawaiian's shares surged more than 11% on Tuesday after Alaska's announcement. The stock has nearly doubled over the past year, while rivals' shares have dropped.

The two airlines said in December when they announced the deal that they would keep each carrier's brand but operate under a single platform, combining into a more than 360-airplane fleet covering over 130 destinations.

The Transportation Department said Tuesday it "is reviewing the application and can only approve a transfer if it is in the public interest."

The Justice Department didn't immediately comment.

Correction: Hawaiian's stock has nearly doubled over the past year, while rivals' shares have dropped. An earlier version misstated the time period.