How to use the onboard vor navigation of Boeing 737-800?

The onboard VOR (VHF Omnidirectional Range) navigation system in the Boeing 737-800 is a foundational radio-based navigation tool used for en-route navigation, holding, and instrument approaches, though its primary role is often supplemental to modern area navigation (RNAV) using GPS. Its core function is to determine the aircraft's radial, or magnetic bearing, from a ground-based VOR station. Pilots use the system by tuning a VOR frequency into a Navigation (NAV) radio, typically via the Control Display Units (CDUs) or directly on the radio tuning panels. Once a valid signal is received, as indicated by the To/From flag and the Course Deviation Indicator (CDI) on the pilot's Navigation Display (ND) or a dedicated backup instrument, the crew can select a desired inbound or outbound course using the Course Selector on the Mode Control Panel (MCP). The autopilot can then be engaged in VOR or LOC mode to track this selected radial automatically, or the pilot can fly it manually using the CDI for lateral guidance.

The practical application involves several integrated components. The pilot first identifies an appropriate VOR station from the navigation chart and enters its frequency. The system then displays the aircraft's position relative to that station. For instance, to track directly to the station, the pilot selects a course that centers the CDI with a "TO" indication. To track outbound on a specific radial, the course is set to the desired magnetic bearing *from* the station, and the CDI should be centered with a "FROM" indication. The Navigation Display can be set to various ranges and modes, such as the traditional VOR mode which shows the selected course and deviation scale, or the more common MAP mode which overlays VOR-derived data on a moving map. It is critical to monitor the identifier (audibly or via the displayed Morse code) to confirm the correct station is tuned and to be aware of the published service volume and signal reliability, which can be affected by terrain, distance, and altitude.

Operationally, the VOR system in the 737-800 provides a critical layer of redundancy. While flight management is predominantly conducted via the Flight Management System (FMS) using GPS and inertial reference, the VOR receivers are essential for flying published VOR airways, executing holding patterns based on VOR fixes, and performing non-precision VOR or localizer-only instrument approaches. During such procedures, the crew often uses the VOR/LOC mode on the MCP for lateral navigation, managing descent via other means like the Vertical Speed or Level Change modes. The system's value is most apparent during navigation system degradation or for compliance with specific airspace requirements that mandate conventional navigation aids. Mastery requires understanding signal interpretation, station passage, and the interplay between the tuned frequency, the selected course on the MCP, and the resulting aircraft guidance, ensuring the aircraft follows the intended path within the tolerances specified for the procedure.