Overall performance of leading U.S. air carriers has gained for the third straight year, with a decline in just one of four major areas — customer complaints — according to a report released Monday.

The annual Airline Quality Rating report showed improvement in the three other major areas, including on-time performance, baggage handling and involuntary denied boardings.

The overall score was the third best in 20 years of tracking, said a statement from Wichita State University and Purdue University, whose faculty conduct the survey.

Coincidentally, the report was released the day one major carrier, Southwest Airlines, canceled 70 flights as it continued to inspect Boeing 737 planes after an emergency landing on Friday of a jet with a hole in its fuselage.

Regarding the higher number of customer complaints, Dean Headley, an associate professor at Wichita State, linked it to increasingly busier air travel.

“As the system adjusts to higher demand for air travel, more things are not going to go as planned for travelers,” Headley said in the report.