Final answer:
The pitot-static system must be calibrated within the last 24 calendar months for an aircraft to be eligible for IFR flight, as required by Federal Aviation Regulations.
Step-by-step explanation:
The pitot-static system is a crucial component in aviation, specifically used for Instrument Flight Rules (IFR) flying. This system provides the pilot with important flight information such as airspeed, altitude and vertical speed, which is indispensable for navigation when flying without outside visual references. According to Federal Aviation Regulations (FARs), the pitot-static system must be checked and calibrated for accuracy within the preceding 24 calendar months before the aircraft can be used for IFR flight.