50-12-01 HAMILTON STANDARD: Applies to All Aircraft Equipped With Continental Engines, Models W-670-6A (R-670-3, -5), W-670-6N (R-670-4), W-670-16 (R-670-8, -11, - 11A) and Hamilton Standard Ground Adjustable Propellers Having Blades, Model 11C1 (Navy 4350, 4350F, 4350F1).
Compliance required not later than April 15, 1950.
To minimize the possibility of propeller blade shank fatigue failures as a result of noncompliance with a mandatory engine operation restriction, the following precautionary measures should be taken:
(1) Check the marking on the engine tachometer and correctly mark it, if necessary, with a red arc which covers the entire r.p.m. range above the higher side of the 1,900 r.p.m. graduation.
(2) Install placard in aircraft to read: "Avoid all engine operation above 1,900 r.p.m. except during takeoff".
(3) Check position of the propeller and correctly index, if necessary, in the zero degree position (blades in line with crankthrow).