Two Democratic senators are probing recent massive flight delays caused by airline information technology issues.

Sens. Richard Blumenthal of Connecticut and Edward Markey of Massachusetts sent an open letter on Tuesday asking 13 airlines if they are taking efforts to improve their systems and ensure that passengers are given more options to get to their destinations if such massive technology failures occur again.

"We are concerned with recent reports indicating that airlines' IT systems may be susceptible to faltering because of the way they are designed and have been maintained," they wrote in the letter. "Now that four air carriers control approximately 85 percent of domestic capacity, all it takes is one airline to experience an outage and thousands of passengers could be stranded, resulting in missed business meetings, graduations, weddings, funerals and other prepaid events."

Among the recipients were the CEOs of Southwest Airlines and Delta Air Lines, both of which recently experienced significant technology failures leading to the cancellation of thousands of flights. They are two of the four biggest U.S. carriers that the lawmakers referred to in the letter, with the others United Airlines and American Airlines.

"In light of these recent technology issues, we encourage you to ensure that your IT systems have the appropriate safeguards and backups in place to withstand power outages, technological glitches, cyberattacks and other hazards that can adversely affect IT systems," they wrote.

The lawmakers asked the airlines to respond to a number of questions including the specific causes for the disruptions, whether the carriers have policies to rebook passengers for no charge on flights with other airlines or different modes of transportation, and if they have other accommodations for inconvenienced customers.

"Airlines are reaping record profits while neglecting major system weaknesses, and passengers are stuck paying the price," Blumenthal said in a statement. "Airlines are still relying on software from the 1960s — outdated and inadequate technology prone to glitches and meltdowns that have paralyzed air travel and disrupted our global economy." He said air carriers "must invest now in 21st-century technology and commit to transparent and fair consumer protections in the event of any future breakdowns."‎