The flight management computer (FMC) is operated through the control display unit (CDU). Read the current page and its labels before entering data: the same key can perform different functions on different pages.
Current cockpit interface
Read the display with read_group, using {"group": "fmc-cdu"}. This returns the title, line labels, displayed values, scratchpad and execute light. Use cockpit_fmc_cdu for key presses and text entry. For example:
Read the resulting page before proceeding; the installed SMART INIT REF option can change the destination. Enter text with action: "cdu-type" and a text field. Select the physical left or right line key with actions such as lsk-1l or lsk-1r. The complete FMC control catalog lists the available keys and readings.
Captain CDU
Use cockpit_fmc_cdu to enter text and press CDU keys. Read fmc-cdu with read_group to inspect the current page and scratchpad. The control catalog lists the supported keys and displayed fields.
Line-select keys refer to physical positions. Their function depends on the current page; lsk-1l does not always select the same field. Check the page labels before pressing it. Read the scratchpad before typing and verify the destination field after selecting a line key.
Enter and verify data
- Obtain control of the CDU for the intended entry. Read the page title, relevant labels and values, and scratchpad.
- Confirm the intended page and field. Obtain the required value and format from the applicable procedure or mission data.
- Enter the value. Verify the scratchpad before selecting the associated line-select key.
- Read the destination field and any resulting message. Confirm the value was accepted in the intended field.
- If a modification is pending, review its scope before EXEC. Verify the accepted active result after execution.
If the page changes or CDU ownership changes, reacquire the page and field context before continuing. Do not clear a message without interpreting it. A displayed EXEC light is not authority to accept an unidentified modification.
Check the page before interpreting its fields
Interpret displayed position values only after reading the page title and field labels. If the page changes, read it again before using those values. A position shown on a CDU page is not an independent position sensor.
Preflight data
The source CDU preflight has three checks: Initial data — Set; Navigation data — Set; Performance data — Set. Use the applicable detailed page procedure to complete and verify each group. A successful text-entry or EXEC action alone does not satisfy the group.
Arrival and approach
Before top of descent, make the required arrival-route modification and verify arrival RNP. During descent preparation, enter the applicable VREF on APPROACH REF and set or verify navigation radios. During approach, update RNP as needed. Retain the source conditions for each item.
Select one approach family: ILS, IAN or VNAV. Do not execute all landing families in document order. A displayed route is not an ATC clearance or confirmation that the scenery agrees with navigation data. Use the assigned clearance and navigation references.
Verify the selected landing reference
- Read the current CDU page. Use INIT REF and the displayed page links to reach APPROACH REF; verify the title instead of assuming that one key always opens it.
- Read the displayed landing weight, units, flap choices and associated reference speeds. Compare the weight and intended flap setting with the current flight’s performance inputs.
- Enter or select the applicable flap/VREF pair using the field labels on that page. Follow the data-entry checks above: scratchpad contents are pending input, not an accepted landing selection.
- Read the accepted flap and VREF fields again. Keep the reference speed separate from any required approach-speed correction. Verify the final speed target on the mode control panel (MCP) after setting it.
The landing-performance inputs also include wind, runway condition, braking and required landing length. This chapter explains entry and verification; it does not supply the missing speed-correction rules or a complete landing-distance calculation. Those inputs must be resolved before the documentation can support a complete landing-performance decision. Last modified on October 30, 2026
