What is the appropriate step to take when reporting a safety incident on board?

Documenting the details of a safety incident and reporting them to the captain is the appropriate step because it ensures that the information is accurately recorded and communicated to the highest authority on board. The captain is responsible for the safety and security of all passengers and crew, and timely reporting allows for immediate assessment and action, if necessary. This chain of command is critical in addressing safety issues effectively and maintaining a secure environment during the flight.

In contrast, whispering details to another passenger can lead to miscommunication and does not bring the incident to the attention of those who can take action. Filing a complaint after the flight delays necessary response and resolution during the time the issue is relevant. Posting on social media is inappropriate and can escalate a situation rather than resolving it, plus it may compromise privacy and security protocols.