§25.925 Propeller clearance

Unless smaller clearances are substantiated, propeller clearances with the aeroplane at maximum weight, with the most adverse centre of gravity, and with the propeller in the most adverse pitch position, may not be less than the following: (a) Ground clearance. There must be a clearance of at least 18 cm (7 inches) (for each aeroplane with nose wheel landing gear) or (23 cm 9 inches (for each aeroplane with tail-wheel landing gear) between each propeller and the ground with the landing gear statically deflected and in the level take-off, or taxying attitude, whichever is most critical. In addition, there must be positive clearance between the propeller and the ground when in the level take-off attitude with the critical tyre(s) completely deflated and the corresponding landing gear strut bottomed. (b) Reserved. (c) Structural clearance. There must be – (1) At least 25 mm (1·0 inches) radial clearance between the blade tips and the aeroplane structure, plus any additional radial clearance necessary to prevent harmful vibration; (2) At least 13 mm (0·5 inches) longitudinal clearance between propeller blades or cuffs and stationary parts of the aeroplane; and (3) Positive clearance between other rotating parts of the propeller or spinner and stationary parts of the aeroplane.