The main responsibilities of a flight attendant are to ensure passenger safety and security. Their other duties may include serving food and beverages and attending to passenger needs. Even without onboard services, flight attendants are still required. Performance is difficult to measure but can be based on passenger complaints and commendations. Crews undergo annual retraining and are considered to have "normal" performance unless otherwise indicated. Reporting structures vary by airline but generally include junior attendants, senior crews, supervisors, and fleet controllers overseeing aircraft groups. Flight attendant activities are divided into preflight briefing and preparation, passenger reception, in-flight duties like safety demonstrations and meal services, and post-landing tasks before reporting.