U.S. equities slumped at midday Monday as investors appeared to be taking advantage of 2024's big stock gains ahead of the last day of the year. The Dow Jones Industrial Average, S&P 500, and Nasdaq all lost about 1%.

Boeing (BA) was one of the worst-performing stocks in the Dow after South Korean officials ordered inspections of the plane maker's 737-800 aircraft following this weekend's deadly crash of a Jeju Air flight.

Shares of MicroStrategy (MSTR) tumbled when the biggest corporate holder of bitcoin announced it had sold more than 592,000 shares, and used the $209 million raised to buy more of the cryptocurrency.

Archer Aviation (ACHR) shares sank after the electric vertical takeoff and landing (eVTOL) aircraft maker backed by United Airlines (UAL) said it was doubling the number of common stock available and changed board membership requirements.

Energy companies, including EQT (EQT) and Coterra Energy (CTRA), dominated the list of top gainers in the S&P 500 as natural gas prices skyrocketed on expectations of big demand because of colder weather ahead for the U.S. and Europe.

Nvidia (NVDA) was the only Dow stock in positive territory. Shares advanced when the artificial intelligence (AI) chipmaker completed its acquisition of Israel-based AI infrastructure firm Run:ai.

Shares of another AI-related company, Palladyne AI (PDYN), took off after the manufacturer of software for robots reported a drone using its technology successfully tracked a moving target for the first time.

Oil futures were up. Gold prices were little changed. The yield on the 10-year Treasury note was down. The U.S. dollar rose versus the euro and pound, but lost ground to the yen. Major cryptocurrencies traded lower.