Yankee or Zulu flight rules. Y flight rules means that the first part of the flight is IFR, thereafter the flight is conducted in VFR. Z flight rules means that the first part of the flight is VFR, thereafter the flight is conducted in IFR.

In the world of aviation and flight planning, Y and Z are specific codes used to indicate a change in flight rules during a journey. Y Flight Rules mean the flight begins under IFR (Instrument Flight Rules) and later switches to VFR (Visual Flight Rules). This is common when a pilot departs a major airport in bad weather but expects clear skies at a smaller, uncontrolled destination. Conversely, Z Flight Rules mean the flight starts under VFR and later switches to IFR. This is often used for "VFR Departures" from rural airfields where the pilot intends to pick up an IFR clearance once they reach a certain altitude or a controlled airspace boundary. In 2026, these codes are essential for air traffic controllers to manage transitions safely, and pilots must specify the exact "Changeover Point" in their digital flight plan to ensure seamless handoffs between various sectors.