Delta Air Lines canceled significantly fewer flights Wednesday, and the airline’s chief executive said cancellations and delays stemming from a global technology breakdown should end by Thursday.

The airline issued a message from Ed Bastian to customers while the CEO was in Paris to attend the Summer Olympics.

In the message, Bastian apologized to travelers who had their plans upended. Delta has canceled more than 6,500 flights — far more than any other airline — since key systems were crippled by the technology outage.

“While our initial efforts to stabilize the operations were difficult and frustratingly slow and complex, we have made good progress this week and the worst impacts of the CrowdStrike-caused outage are clearly behind us,” Bastian said.

CrowdStrike is the cybersecurity company whose faulty software update sent to computers running on Microsoft Windows led to grounded flights and disrupted banks, hospitals and retailers starting early Friday.

The U.S. Department of Transportation is investigating why Delta failed to recover as quickly as other airlines. Transportation Secretary Pete Buttigieg said that the department would also examine Delta’s customer service, including “unacceptable” lines for assistance and reports that unaccompanied minors were stranded at airports.

Buttigieg said the department had received more than 3,000 complaints about Delta since the outage started.

By midday Wednesday, Delta had canceled about 50 flights, not counting those on its Delta Connection regional affiliates, according to tracking service FlightAware. That was down from more than 500 cancellations, or 14% of its schedule, on Tuesday.

As recently as Sunday, three out of every four Delta flights were either canceled or delayed.

Bastian said Delta anticipates Thursday will be “a normal day, with the airline fully recovered and operating at a traditional level of reliability.”

The CEO said Delta is committed to taking care of customers whose flights are affected, “with meals, hotel accommodations and ground transportation offered through vouchers and reimbursements.” Those passengers also will receive airline miles and travel vouchers “as a further gesture of apology,” he said.

Bastian was in Paris for the Olympics, which open Friday. Delta is the airline sponsor of the U.S. Olympic team, and the airline said he was meeting with business partners while in Paris.

“Ed delayed this long-planned business trip until he was confident the airline was firmly on the path to recovery,” a Delta spokesperson said in a statement. “As of Wednesday morning, Delta’s operations were returning to normal. Ed remains fully engaged with senior operations leaders.”

Bastian flew to Paris on a regularly scheduled Delta flight, the Atlanta-based airline said.

U.S. Sen. Maria Cantwell, D-Washington, who chairs the Senate commerce committee, wrote a letter to Bastian on Tuesday telling him her committee would conduct oversight into the underlying reasons for the outage. She said the committee would seek answers from the airline industry about “ensuring redundancy to prevent future widespread outages as the global and national impacts on air travel and the flying public are far too important.”