Definition
A dual concentric control knob on a Garmin G1000 (or similar) Primary Flight Display and Multi-Function Display used to access and manipulate the Flight Management System pages. The outer (large) knob typically moves between page groups or fields, the inner (small) knob moves within a group or changes a value, and pressing the knob usually activates the cursor for data entry or selection.
Plain English
A two-in-one knob on the glass cockpit display that lets you open flight management pages, move a cursor around, and select or enter information. You turn the outer ring to jump between sections, turn the inner ring to scroll within a section, and push it in to start typing or to confirm a choice.
Context Anchor
Seen on glass-cockpit displays when using screen menus, including the nearest-airports page on the primary flight display.
Derivation
FMS stands for Flight Management System — the onboard computer that handles navigation, flight planning, and performance data. The knob is named for the system it primarily controls.
Why Pilots Care
It lets the pilot quickly manage flight plans and navigation data without looking away from the displays or using many separate buttons.
Intuition Check
Do not assume the FMS knob directly flies the airplane. In this context, it is mainly a display and data-entry control.
Example Sentence 1
To find the nearest airport on the PFD, the pilot pressed the FMS knob to activate the cursor, then turned the small inner knob to scroll through the list.
Example Sentence 2
She used the FMS knob to scroll through the list of available approaches and confirm the choice.