Final answer:
Near misses with other aircraft must be reported to the NTSB if detected by an Airborne Collision Avoidance System (ACAS). Other options listed are not required unless they are directly involved in a reportable incident or accident.
Step-by-step explanation:
Which of the following must be reported to the NTSB, for aircraft equipped with an Airborne Collision Avoidance System (ACAS)? The correct answer is c) Near misses with other aircraft. According to the National Transportation Safety Board (NTSB) regulations, specifically under 49 CFR Part 830 - Notification and Reporting of Aircraft Accidents or Incidents and Overdue Aircraft, and Definitions, one of the incidents that must be reported is an aircraft collision in flight which is often detected by the ACAS. This system is designed to reduce the risk of mid-air collisions between aircraft by issuing resolution advice to pilots when the system detects a potential collision with another aircraft.
While engine malfunctions, weather conditions, or passenger complaints may be significant events, they are typically not reportable to the NTSB unless they directly contribute to an accident or incident as defined by the NTSB's reporting requirements.