47-26-02 CESSNA: (Was Mandatory Note 10 of AD-768-4.) Applies to 120 and 140 Aircraft Serial Numbers 8000 to 13777, Inclusive.
Pending compliance with this note the following placard shall be installed immediately on the instrument panel: "ALL ACROBATICS PROHIBITED. REDUCE CRUISING AIRSPEED IN ROUGH AIR."
Compliance with modifications listed below required prior to August 1, 1947. After August 1, placard is not valid, and airplanes are not to be flown until modifications are accomplished.
Inspect the wing leading edge for indications of buckling in the skin which may result from failure of the spot welds attaching the skin to the nose ribs. If there is any buckling of the skin at the ribs, other than at the extreme nose radius, the fabric should be cut open on the bottom surface just forward of the front spar for thorough inspection of the affected nose ribs. Any buckled nose ribs should be repaired or replaced. Upon completion of the above the following reinforcements should be accomplished:
1. Leading Edge -
(a) On covered wings install four Cherry CR 163-4-4 rivets in the upper surface leading edge at each nose rib from No. 2 to No. 10 inclusive. No. 30 holes should be drilled through the fabric skin and rib flange at chordwise locations determined by use of a template supplied by Cessna. (If template is not available holes can be located by finding 3/32- inch jig hole (or flush rivet in early airplanes) in leading edge skin at tip of each nose rib and drilling holes 1 1/2 inches, 2 3/4 inches, 4 inches, and 5 1/4 inches aft from the jig hole as measured along the curved surface of the leading edge, and exactly in line with the jig hole and the rivet through the skin and nose rib flange just forward of the front spar.) Use only light pressure on drill to avoid bending rib flange where spot welds have failed. Be sure that hole is drilled through both the skin and the nose rib flange.
(b) On wings being recovered the Cherry rivets should be carefully drilled out before removing the fabric. Before the new fabric is applied AN 456-AD4 rivets should be installed.
2. Upper Surface Fabric Attachment -
(a) On covered wings install four Cherry CR 163-4-4 rivets in each rib one rivet midway between each of the fabric attachment clips (5 inches clip spacing) from No. 1 to No. 5, as numbered aft from the front spar. No. 30 holes should be drilled for the rivets through the fabric at the middle of the reinforcing tape and through the rib flange. A 7/16-inch x 0.015- inch pyralin washer should be used under each rivet head and should be stuck to the fabric with dope. On wings having PK screws installed in accordance with Cessna Service Letter Nos. 35 and 37, replacement of the screws with Cherry rivets is optional.
(b) On recovering wings, the rivets should be carefully drilled out before removing the fabric to prevent damage to the ribs. When the new fabric covering is applied, standard Cessna fabric attachment clips may be substituted for the Cherry rivets of PK screws. In this event a clip should be installed midway between each of the present clips from the front spar to the rear spar and from the rear spar to the trailing edge. Holes for the additional clips should be made with a No. 40 drill and a template supplied by Cessna.
(Cessna Service Letter No. 42 dated May 20, 1947, also covers this subject and supersedes Cessna Service Letters Nos. 37 and 28.)