Definition
The normal forward-thrust operating range of a turboprop engine, in which the propeller blade angle is controlled by the pilot's power lever and the propeller governor maintains a constant selected RPM by varying blade pitch. Alpha mode covers all flight operations from takeoff through landing, but does not include ground operations such as reverse thrust or beta range taxi control.
Plain English
The normal flight setting on a turboprop engine. The pilot moves the power lever to ask for more or less thrust, and the propeller automatically adjusts its blade angle to hold a steady RPM.
Context Anchor
Seen in turboprop aircraft systems, especially when learning power lever ranges, propeller control, flight idle, and ground handling limits.
Derivation
From the Greek letter alpha, the first letter of the Greek alphabet, used in engineering to label the first or primary mode of something. Alpha mode is the primary, in-flight operating mode of a turboprop; beta mode is the secondary, ground-handling mode.
Why Pilots Care
Knowing whether the engine is in alpha or beta mode tells the pilot how the propeller will respond to power lever movement. In alpha mode, the lever controls power; in beta mode, the lever controls blade angle directly. Mixing them up on the ground or in flight can cause loss of control or engine damage.
Intuition Check
Alpha does not mean angle of attack here. Here it means the normal flight operating range of a turboprop propeller system.
Example Sentence 1
Once airborne and the power levers were advanced past the flight idle gate, the engines were in alpha mode for the remainder of the climb and cruise.
Example Sentence 2
During the preflight, the checklist confirmed the system was still in Alpha Mode after the last maintenance check.