Definition
The flat or nearly flat surface of a propeller blade that faces rearward, away from the direction of flight, when the propeller is installed on the aircraft. It is the side a person standing behind the aircraft sees when looking at the propeller.
Plain English
The rear-facing side of a propeller blade — the side you see when you look at the propeller from behind the airplane.
Context Anchor
Used during propeller inspection, repair, and blade-description discussions in aircraft maintenance.
Derivation
Back comes from an old English word meaning the rear or outside surface of something. In propeller wording, it is used as a named surface of the blade, so the helpful point is not direction but which side of the blade is being described.
Why Pilots Care
During preflight and maintenance inspections, nicks, cracks, and erosion are reported by location — back versus face. Knowing which side is which ensures damage is described accurately and the correct repair limits are applied.
Intuition Check
Do not assume back means the side facing the tail. Here, back means the curved surface of the propeller blade.
Example Sentence 1
The technician found a small nick on the back of the number two blade and measured it against the manufacturer's repair limits.
Example Sentence 2
Damage on the back of the blade can disrupt airflow and reduce thrust.