Definition
The plural form of Flight Management System (FMS) — the onboard computer systems that integrate navigation, performance, and guidance data to manage an aircraft's flight path. Each FMS combines inputs from sensors such as GPS, inertial reference units, and radio navigation aids with a stored database of airports, airways, procedures, and waypoints to compute lateral and vertical flight paths, fuel burn, and time estimates. The plural is used when referring to multiple units (often two installed for redundancy in a single aircraft) or to FMSs across different aircraft.
Plain English
FMSs are the flight computers that plan and manage where an aircraft flies and how it gets there. The 's' just means more than one — either two computers in the same aircraft, or the systems used across many aircraft.
Context Anchor
Seen in aircraft equipment descriptions, instrument procedure notes, route planning, and cockpit navigation discussions.
Why Pilots Care
They lower workload on complex routes, improve fuel efficiency, and maintain precise navigation even when the pilot is busy with other tasks.
Intuition Check
Do not read FMSs as just a display screen. An FMS is the system behind the route planning and guidance; the screen is only one way the pilot works with it.
Example Sentence 1
After receiving the reroute, the crew updated both FMSs and verified the new flight plan matched on each side.
Example Sentence 2
Both aircraft in the formation had FMSs that allowed them to follow the same fuel-efficient track.