Which system provides critical data for safe altitude maintenance during flight?

The pitot-static system is essential for providing critical data related to altitude maintenance during flight. This system works by measuring air pressure from both the pitot tube and static ports on the aircraft. The pitot tube measures dynamic pressure, which helps determine airspeed, while the static ports measure static pressure, which is vital for determining altitude.

The altimeter, an instrument linked to the pitot-static system, uses the current barometric pressure to provide a reading of the aircraft's altitude. As the aircraft ascends or descends, the changes in static pressure replace the existing pressure readings, allowing the altimeter to accurately reflect altitude changes. This system is crucial for flight safety as it ensures that pilots maintain the appropriate altitude to avoid terrain and other aircraft.

While the navigation system provides location and course information, and the autopilot system can help maintain a specific altitude or flight path, it is the pitot-static system that directly provides the altitude data needed for safe flight. The flight data recorder, on the other hand, is primarily used for post-flight analysis rather than for real-time altitude maintenance. Thus, the pitot-static system is the correct answer for this query, as it is specifically designed to ensure accurate altitude measurement during flight.