CHICAGO — American Airlines on Monday wasn’t claiming “mission accomplished” just yet in its perilous integration of passenger reservation systems with merger partner US Airways over the weekend, but a lack of significant glitches and flight delays has the transition looking like a success.

“We’re pleased with the customer feedback and our operational performance since Saturday, but we’re not letting our guard down especially as we head into the beginning of the week that is busy with business travelers,” said American spokeswoman Leslie Scott. “One of the biggest lessons learned from others was that the days following are equally as important as cutover day itself, so no one is declaring mission accomplished yet.”

According to American’s numbers, nearly 90 percent of weekend flights arrived on time, a high percentage even for a normal fall day.

The US Airways brand flew into the sunset Saturday as American Airlines, now the world’s largest carrier, integrated passenger reservation systems, often called the computer backbone or brain of an airline.

The combined airline has moved to one website, one mobile app and a single set of travel policies and frequent-flier benefits. Fort Worth, Texas-based American and US Airways merged in late 2013.

In other airline mergers, combining systems has caused problems. Notably in 2012, Chicago-based United Airlines combined reservation systems, moving to Continental’s. It resulted in months of rampant delays and cancellations that led to customer defections and damaged profits.

American Airlines officials said last week that they have spared no expense to decrease the chances the airline would have trouble Saturday but couldn’t guarantee complete success.

Several years of other behind-the-scenes integration work is left to complete, involving flight attendants, pilots and maintenance teams. It will take a couple of years to repaint US Airways aircraft.