Definition
The normal flight operating range of a turbopropeller engine, in which the propeller blade angle is controlled by a governor to maintain a selected engine RPM as power is varied. Alpha mode covers all operations from takeoff through landing rollout down to the point where the pilot selects the beta range.
Plain English
Alpha mode is the regular flying setting on a turboprop. The propeller blades automatically twist to the right angle to keep the engine spinning at the RPM the pilot has chosen, no matter how much power is being used.
Context Anchor
Seen in turboprop operations when comparing normal flight power settings with beta range and reverse thrust, especially during landing rollout and ground handling discussions.
Derivation
From the Greek letter alpha, the first letter of the Greek alphabet, used here to label the primary or normal operating range. Beta, the second letter, labels the secondary range used on the ground for taxi and reverse. The naming follows a simple sequence: alpha first, then beta.
Why Pilots Care
Pilots must recognize when the propeller is in alpha mode so they do not attempt reverse or beta selection while airborne or above safe ground speeds.
Intuition Check
Alpha mode does not mean angle of attack here. Here, alpha means the normal forward-thrust propeller operating mode, not the airplane’s nose angle or wing angle.
Example Sentence 1
During cruise, the propeller was in alpha mode, with the governor adjusting blade angle to hold 1,900 RPM as the pilot reduced power.
Example Sentence 2
After landing, the pilot waits for the propeller to reach the low-pitch stop in alpha mode before moving the power lever into the beta range.