Less than 24 hours after United Airlines was forced to order a ground stop on all mainline domestic flights for a little more than an hour, Senators Edward J. Markey (D-Mass.) and Richard Blumenthal (D-Conn.)—members of the Commerce, Science, and Transportation Committee—want answers.

The Senators on Monday sent a letter to United Airlines CEO Oscar Munoz inquiring about the state of the airline’s Information Technology (IT) system in light of Sunday’s computer failure and flight disruptions.

United suffered yet another computer-related problem that forced a brief ground stop for all domestic mainline flights, the airline said in a brief statement, calling it an “IT issue.” The ground stop lasted less than two hours, and flights resumed around 9:15 p.m. EST.

In the letter, the Senators requested information on the nature of the IT failure and what safeguards and backups were in place to prevent such an issue from occurring.  The Senators also asked about how United Airlines accommodated impacted passengers, including reimbursement and compensation offerings.

“In a world where consumers can find, purchase, and check in for flights from their smartphones, IT failures should not be grounding entire airline fleets,” wrote Senators Markey and Blumenthal. “Now that three of the four largest air carriers have recently experienced significant disruptions due to IT failures, it is time for airlines to update their IT systems for the jet age.”

READ MORE: Here Is The Full Text Of The Senators’ Letter To United 

This is the second time in three months that United has been forced to ground its fleet after a computer glitch, though, to be fair, other airlines have suffered through technological issues that have resulted in major delays and cancellations—Southwest and Delta in August, and British Airways in September.