INSPECTION OF PROPELLER BLADE AREAS FOR CORROSION-
ALL SENSENICH FIXED PITCH METAL PROPELLERS
COMPLIANCE DATE:
AT ANNUAL OR 100 HR. INSPECTION
DISCUSSION:
Corrosion of aluminum propeller blade surfaces
occurs at varying rates, depending on the condition of the protective finish
and on atmospheric conditions prevalent in the aircraft basing area. It may
appear as a white powder on the blade surface or, in later stages, as tiny
black specks or cavities extending inward from the surface of the metal. The
mechanical effect of corrosion damage is similar to that of sharp-bottom
impact damage, adversely affecting propeller airworthiness. Particular
concern is that older propellers, still finished with anodize and clear wear-
coat finish, do not have the corrosion retarding capability of modern
ALODINE treatment and polyurethane finish. However, flaked or
blistered paint also may indicate existing corrosion.
REQUIRED ACTION:
A) Carefully remove all flaked or blistered paint from
propeller surface, taking care not to scratch the aluminum surface.
Inspect propeller blades for corrosion. Propeller blades that show less
than 6 square inches of total corrosion (an area the size of a folded
dollar bill) must be repaired in accordance with the following
instructions:
1) Sand the area with 220 wet-or-dry abrasive paper until all
evidence of corrosion is removed.
2) Polish the area with 320 grit (or finer) to remove
all scratches.
3) Clean the area thoroughly, apply an approved penetrant, and
inspect with a l0X glass. NOTE: It is extremely important that all
corrosion be completely removed. If cavities reappear during penetrant
inspection, the repair operation must be repeated.
4) Remove penetrant from affected area with M.E.K.
5) Apply ALODINE or equivalent treatment in accordance with
manufacturer's instructions (proper ALODINE treatment will leave a smooth
amber/gold tint on the aluminum surface after the ALODINE solution has been
rinsed off) .
6) Apply a primer over the repaired area. Note that some
primers are intended for pretreated aluminum, while others are not - and may
result in loss of adhesion of the outer coat.
7) Spray area with matching paint to better protect against
corrosion.
B) If blades show greater than 6 square inches of corrosion, the
propeller must be returned to an approved FAA-Propeller Repair Station for
reconditioning.
C) The recommended flight-time between reconditioning of
SENSENICH fixed-pitch metal propellers is 1000 Hours, PROVIDED IT HAS NOT
RECEIVED PRIOR DAMAGE REQUIRING IMMEDIATE ATTENTION. This removes fatigued
surface metal and the accumulation of small nicks and cuts. The SENSENICH
SERVICE MEMO dated April 8, 1970 is superseded by this recommendation.
Refer to the SENSENICH METAL PROPELLER REPAIR MANUAL (SCRM 478) and AC 20-17D for further
information.
To Download Service Bulletin R-15a in Acrobat (.pdf) Format
