As a record number of people took to the skies in the U.S. last year, the airline industry found customer satisfaction edged lower.

The annual Air Travelers in America Survey by an industry trade group found 81 percent of those questioned were satisfied with their overall travel experience. That is down from 85 percent in 2016.

The drop in satisfaction may not be a surprise since airplanes are more crowded than ever as a healthy economy and relatively low airfares have convinced many to take more flights.

In fact, last year there was an increase in annual trips by every age group and household income, with the exception of those who earned more than US$150,000, according to Airlines for America.

The survey found the biggest jump in trips came from households earning US$75,000--US$99,999. Last year, people in that category took an average of 5.1 trips, up from 3.4 trips in 2016.

"The strides airlines are making to improve the flight experience--from varying fares that can fit any budget, in-flight entertainment options, gourmet food offerings and advancements in technology, both on the ground and in the air-- are resonating with customers and leading to more Americans traveling more often by air," said John Heimlich, vice president and chief economist at Airlines for America.

The survey of 5,046 travelers comes after a year when the industry was hit by several high-profile incidents where passengers clashed with flight crews. The most notable happened in April 2017 when a United Airlines passenger was bumped from a flight and dragged off the plane. The incident was captured on video.

United Airlines ultimately reached a settlement with the passenger and apologized for the incident. The video and controversy led to United and other airlines dramatically altering their policies for bumping passengers off of oversold flights.