Which step is not part of operating the infant flotation device?

The step that is not part of operating the infant flotation device is securing the device to the aircraft. The primary focus of operating an infant flotation device involves ensuring the device is properly positioned and ready for use in emergency situations rather than being secured to the aircraft itself. The other steps, such as placing the neck strap over the infant's head, ensuring the guardian knows how to inflate the device, and attaching the crotch strap to the buckle, are directly related to preparing the flotation device for immediate use in case of an emergency. These actions are crucial for ensuring the safety of the infant during a water landing, as they help to guarantee that the flotation device is correctly fitted, functional, and understandable for the guardian.