59-16-02: Stabilizer Spar

59-16-02 LOCKHEED: Applies to Models 18, PV-1 and B-34 Series Aircraft Except Those Incorporating Spar Reinforcement as Covered in Lockheed Aircraft Service Bulletin 18/SB- 112. Compliance required as indicated. Numerous reports have been received wherein fatigue cracks have been found in the horizontal stabilizer spars in the area of the vertical fin attachments. In order to determine if this condition has developed, the following inspection is required. Within the next 50 hours of flight and at 300-hour intervals thereafter inspect the horizontal stabilizer front and rear spar flanges and webs for cracks in the region of the vertical fin attaching angles. If cracks are found, stop-drill, install spar flange and web doublers and flange filler blocks extending beyond the fin attaching angles. Add doubler plates on the forward face of rear spar in region of rudder hinge bracket attachment holes. Visual inspections of the area with a 10-power glass are adequate. The 300 hour inspection may be discontinued after incorporation of the reinforcements. One approved method of accomplishing the above spar reinforcement is contained in Lockheed Aircraft Service Bulletin 18/SB-112 dated September 18, 1944, pertaining to this same subject. Revised May 27, 1965.