B737 VHF-NAV, IRS, FMC Switch

VHF NAV Transfer Switch

The VHF NAV transfer switch changes the source of the data that the DPCs use for the navigation displays. The switch transfers the following data: DME, ILS/GLS, VOR, and MCP course.

• BOTH ON 1 – the DPCs use Multimode Receiver 1 as the source for the captain’s display and first officer’s display.
• NORMAL – Multimode Receiver 1 supplies data for the captain’s display and Multimode Receiver 2 supplies data for the first officer’s display.
• BOTH ON 2 – the DPCs use Multimode Receiver 2 as the source for the captains display and first officers display.

Note: The Digital Flight Control System cannot use VOR/ILS data that is not shown on the displays. Thus, when the Autopilot (A/P) system is engaged the VHF Navigation Control must match the primary Autopilot system that is ENGAGED for proper ILS/VOR operations; i.e. (CMD A uses VHF NAV 1 for control and CMD B uses VHF NAV 2 for control).

IRS Transfer Switch

• BOTH ON L – switches the flight instruments attitude and heading source to left IRS.
• NORMAL – flight instruments attitude and heading source is from default IRS.
• BOTH ON R – switches the flight instruments attitude and heading source to right IRS.

FMC Source Select Switch

• BOTH ON L –
  • Selects left FMC for all FMC operations.
  • Right map will annunciate “FMC L.”
• NORMAL –
  • Left FMC controls CDUs and provides input to the autothrottle system.
  • Right FMC operates in synchronization with left FMC.
  • Maps display composite information from both FMCs.
• BOTH ON R –
  • Selects right FMC for all FMC operations.
  • Left map will annunciate “FMC R.”
• Note: Moving the source select switch will cause LNAV and VNAV to disengage.