United Airlines said it expects to lose money over the 737 Max 9 grounding, the first indication of the financial impact of the door plug blowout saga

• United Airlines is the world's biggest operator of the Boeing 737 Max 9.
• A Monday filing said it expects to lose up to 85 cents per share in Q1.

United Airlines said it expects to lose money as a result of the Boeing 737 Max 9 grounding, in a Monday filing.

It forecast an adjusted loss of between 35 and 85 cents per share for the first quarter of this year.

And it estimated its cost per available seat mile, excluding fuel costs, will rise three percentage points due to the grounding — reducing the airline's efficiency.

United is the world's biggest operator of the 737 Max 9, with 79. Worldwide, there are 171 such jets with a door plug like the one that came off during Alaska Airlines Flight 1282.

Monday's filing is the first fiscal indication of the problems caused by the blowout.

According to Bloomberg, United CEO Scott Kirby has been complaining to colleagues about Boeing — skeptical that the manufacturer can recover.

United is holding its earnings call on Tuesday morning, when it will likely face more questions about the impact of the grounding.

Alaska Airlines, which operates 65 Boeing 737 Max 9 jets, will report its Q4 earnings before the market opens on Thursday.

United's results also delivered some positive news for shareholders as it exceeded Wall Street's expectations.

According to Markets Insider data, United stock was up around 4% in after-hours trading.

The airline also saw its busiest-ever travel period during the last two weeks of the year — flying 8.2 million customers, or a daily average of 483,000. United said Q4 saw its best on-time arrival performance in its history too.