Definition
A range of operation on a turboprop or constant-speed propeller in which the pilot directly controls propeller blade angle rather than engine power. In beta mode, the power lever is moved aft of the flight idle position to manually flatten the blades toward zero thrust, or further into negative (reverse) blade angles, to slow the aircraft during taxi or after landing.
Plain English
A ground-only setting where the pilot moves the propeller blades directly with the power lever to produce little, no, or reverse thrust — used for slow taxi and to help slow down after landing.
Context Anchor
Seen in turboprop aircraft procedures, propeller system descriptions, ground handling, and maintenance discussions of propeller control.
Derivation
In propeller engineering, the Greek letter beta (β) is the symbol used for propeller blade angle. 'Beta mode' literally means 'blade-angle mode' — the regime where the pilot is commanding blade angle directly instead of commanding engine power and letting the governor set the angle.
Why Pilots Care
Using beta mode in flight is prohibited and dangerous — flattening or reversing the blades in the air can cause sudden loss of lift over the wing, loss of control, and structural damage. The power lever has a physical gate at flight idle to prevent accidental entry into beta while airborne.
Grounding Statement
In Beta mode, the propeller is no longer just pulling the airplane forward; it can also be set nearly flat or reversed to help control movement on the ground.
Intuition Check
Do not read “Beta” as meaning experimental or less important. Here it names a specific propeller control mode used mainly on the ground.
Example Sentence 1
After touchdown, the pilot lifted the power levers over the gate and into beta to shorten the landing rollout.
Example Sentence 2
In beta mode the propeller blades can produce negative thrust to help the aircraft turn tightly while taxiing on the ramp.