What does a single tone chime ("ding") usually mean?

A single tone chime, often referred to as a "ding," is typically used to indicate that a call is coming from the lavatory. This sound is designed to alert the flight crew that a passenger is in need of assistance specifically in that area, without causing alarm among other passengers.

In airline operations, communication tools like chimes are standardized to maintain clarity and efficiency in notifications. The single tone for a lavatory call is distinct from alerts meant for emergencies or critical situations, which may use different sounds to ensure immediate response from the crew.

When other options are considered, they are associated with more urgent or different contexts; for example, an emergency announcement would likely trigger a more urgent or attention-grabbing alert. Similarly, a passenger needing assistance might be indicated by a different signal, and flight deck alerts are generally designed to inform the crew of issues requiring immediate operational attention. Thus, the single tone chime serves a specific and important purpose in communication within the cabin framework.