equal to one nautical mile per hour. Mean Sea Level (MSL) The average height of the surface of the sea for all stages of tide; used as a reference for altitude (also see AGL). Nautical mile (NM) A unit of distance used in aviation and maritime navigation, equal to approximately one minute of arc of latitude on a great circle. It is defined to be 1852 metres exactly, or approximately 1.15 statute mile. Route Forecast (ROFOR) A format for reporting weather information. Zero-Fuel Weight (ZFW) The weight of the aircraft with crew, cargo, and passengers, but without fuel. See also Aeronautical Telecommunication Network (ATN) Aircraft Communications Addressing and Reporting System (ACARS) Flight planning Flight service station (FSS) Future Air Navigation System (FANS) International Civil Aviation Organization References External links International Flight Planning Resource by Region Aviation glossary Flight Crew Guide - ICAO Model Flight Plan Form Flight Crew Guide - FAA Flight Plan Form Flight Crew Guide - ATS Flight Plan Flight Crew Guide - Operational Flight Plan Aircraft operations