Definition
On a rotating propeller, the blade that is moving upward through its arc of rotation as it passes one side of the propeller disc. On a typical single-engine airplane with a clockwise-rotating propeller (viewed from the cockpit), the ascending blade is on the left side of the disc; on the right side, the blade is descending. Because of the airplane's pitch attitude in flight, the descending blade meets the relative wind at a higher angle of attack and produces more thrust than the ascending blade, creating an asymmetric thrust line offset from the centerline.
Plain English
It is the propeller blade that is sweeping upward as the propeller spins. On the opposite side of the propeller, the other blade is sweeping downward at the same moment. The two sides bite the air a little differently, which matters for how the airplane handles.
Context Anchor
Seen in multi-engine training when discussing minimum control speed, critical engine, and how propeller thrust can pull the airplane left or right after one engine fails.
Derivation
Ascending comes from a Latin word meaning “to climb up.” Propeller comes from words meaning “to drive forward.” Blade refers to the flat, airfoil-shaped part of the propeller. Together, the phrase points to the propeller blade that is moving upward in its rotation.
Why Pilots Care
The thrust difference between ascending and descending blades on the operating engine increases yaw toward the failed engine, directly raising VMC and affecting which engine is critical.
Intuition Check
Do not read ascending as “the airplane is climbing.” Here, ascending only means the blade is moving upward around the propeller’s circle as it spins.
Example Sentence 1
Because the airplane is flown at a positive pitch attitude, the descending blade produces more thrust than the ascending blade, which is the cause of P-factor.
Example Sentence 2
During single-engine climb the pilot trims to counteract the yaw created by the greater thrust of the descending blade versus the ascending blade.