Most flight attendants work full time, but they usually have variable schedules. Flight attendants often work nights, weekends, and holidays because airlines operate every day and have overnight flights. In most cases, a contract between the airline and the flight attendant union determines the total daily and monthly workable hours. A typical on-duty shift is usually about 12 to 14 hours per day. However, duty time can be increased for international flights. The Federal Aviation Administration (FAA) requires that flight attendants receive 9 consecutive hours of rest following any duty period before starting their next duty period.