Legally, a 3-year-old does not need a car seat (Child Restraint System or CRS) on a commercial aircraft under FAA regulations, as children ages 2 and older are required to have their own seat and may use the standard airplane lap belt. However, the FAA and the National Transportation Safety Board (NTSB) strongly recommend the use of a government-approved CRS or an alternative like the CARES harness for children until they weigh at least 40 pounds. The primary reason is safety during "clear air" turbulence or emergency maneuvers, where a standard lap belt might not properly secure a small child's body. If you choose to bring a car seat, it must have a label stating it is "certified for use in motor vehicles and aircraft." Many parents find that 3-year-olds are more comfortable and better behaved in a familiar car seat, and it also ensures you have a safe seat for them to use in cars once you reach your destination. If a bulky car seat is too much to carry through the airport, the CARES harness is a lightweight, FAA-approved alternative specifically designed for children weighing between 22 and 44 pounds.