Definition
The white-colored band marked on an airspeed indicator that shows the flap operating range. Its lower limit is the power-off stalling speed in the landing configuration (V_S0), and its upper limit is the maximum speed at which flaps may be safely extended (V_FE).
Plain English
The white stripe on the airspeed indicator tells you the speed range where it is safe to have the flaps down.
Context Anchor
Seen on the airspeed indicator during approach, landing, and any time a pilot is checking whether flap use is allowed at the current speed.
Derivation
“Arc” comes from a word meaning a bow or curve. On a round airspeed indicator, the color marking appears as a curved band, so “white arc” means the white curved speed range on the gauge.
Why Pilots Care
Extending flaps outside this range can cause structural damage or handling issues.
Intuition Check
Do not read the white arc as a general “safe speed” range for all flying. In this context, it specifically marks the speed range connected with flap operation.
Example Sentence 1
On final approach, she checked that her airspeed was within the white arc before lowering full flaps.
Example Sentence 2
Slowing into the white arc allowed safe flap deployment for the landing configuration.