Airline seats are shrinking, and the U.S. Department of Transportation is examining the negative effects. Public domain / Cweyer

Airline seats are shrinking -- and that's bad for both your comfort and your safety, some advocates say. That's why the U.S. Department of Transportation convened its consumer advisory group, known as the Advisory Committee for Aviation Consumer Protection, on Tuesday to hear testimony from expert witnesses on the state of airline seats.

Scheduled witnesses included experts from the Federal Aviation Administration's Civil Aerospace Medical Institute, the Centers for Disease Control and Prevention, and the inventor of the Knee Defender, a gadget that prevents the airline seat in front of you from reclining.

The advisory group can make nonbinding suggestions to government regulators.

Safety was a major concern discussed at the hearing. Last summer air travelers squeezed into the least amount of personal space in the history of flying, the Associated Press reported. Representatives from flight attendant unions at the meeting said that tightly packed seats could make it difficult for passengers to evacuate in the event of a plane crash.

The FAA conducts tests on how quickly passengers can evacuate a plane. Cynthia Corbett, an FAA researcher who spoke at the meeting, said the FAA’s tests are based on planes with 31 inches of seat pitch between airplane rows. But most airlines today offer less pitch than that.

Both seat pitch -- the number of inches from a given point on one airline seat to the same point on the seat in the next row -- and seat width in economy class have decreased on planes operated by the nation’s largest carriers (and airlines worldwide) over the last three decades. Meanwhile, many airlines are installing roomier, more luxurious accommodations in premium classes, often at the expense of travelers in coach.

An analysis by USA Today found that American, Delta and United all have some planes with a seat pitch of just 30 inches, while 31 and 32 inches were the minimums in previous years. (Some budget carriers are even worse: On some Spirit planes, seat pitch is just 28 inches.) And the tightest economy seats on American carriers today measure at about 17 inches -- down from a low of 19 inches in the 1990s.

The shrinking seats are evidenced by how airlines are configuring new planes. The Wall Street Journal reported that 70 percent of Boeing 777s delivered in 2012 were configured with 10-abreast seating in coach, up from 15 percent in 2010. Nine-abreast had been the norm until then.