80-04-06 AYRES CORPORATION (formerly Rockwell International and Snow Aeronautical Company): Amendment 39-3688. Applies to the following Ayres Models and serial numbers with 2000 or more hours time in service after the effective date of this AD, certificated in all categories: \n\n\nModel S-2D:\nAll S/N's \nModel S-2R:\nS/N's 1416R through 2560R; S/N's 5000R through 5100R \nModel S2R-T11:\nS/N's T11-001 and T11-002 \nModel S2R-T15:\nS/N's T15-001 through T15-005 \nModel S2R-T34:\nS/N's 6000 through 6049; S/N's T34-001 through T34- 019 \nModel S2R-R3S:\nS/N's R3S-001 through R3S-008\n\n\tCompliance required as indicated unless already accomplished. \n\n\tTo prevent the possible structural failure of the horizontal stabilizer due to a crack or cracks in the tubular front spar, accomplish the following within 25 hours time in service after the effective date of this AD and thereafter at intervals not to exceed 500 hours time in service from the last inspection. \n\n\t1.\tInspection Procedures \n\t\ta.\tRemove fuselage side skins to provide access to the inspection hole in the bottom of the horizontal stabilizer. \n\n\t\tb.\tDisconnect the flying wires, left and right sides, from both upper and lower surfaces of the horizontal stabilizer to permit the exercising of the stabilizer. \n\n\t\tc.\tInspect the horizontal stabilizer front spar tube (P/N 40221-19) in the area of both the left and right fuselage attach bushings as shown in Figure 1 using a flashlight and an inspection mirror. IMPORTANT - the stabilizer must be exercised with both an up and down force at the tip during the inspection to ensure detection of a crack. \n\n\t\td.\tIf the spar is cracked, comply with Paragraph 2. If the spar is not cracked, comply with Paragraph 3. \n\n\t2.\tAction Required If Spar Is Cracked \n\t\tIf the spar is cracked in the area of the front spar-to-fuselage attach bushing, accomplish either Paragraph a. or b. listed below: \n\n\t\ta.\tBefore further flight, replace the cracked horizontal stabilizer assembly P/N 40221-61 with a new horizontal stabilizer assembly P/N 40221-70. When P/N 40221-70 is installed, the repetitive inspections required by Paragraph 1 may be discontinued. \n\n\t\tb.\tBefore further flight, replace the cracked horizontal stabilizer assembly P/N 40221-61 with a serviceable assembly of the same part number. Continue the Paragraph 1 inspection at intervals not to exceed 500 hours time in service from the last inspection. \n\n\t\tReinstall the horizontal stabilizer assembly and adjust the flying wires in accordance with the Rigging Procedures in Section VII of the Maintenance Manual. Finally, adjust the tension in each flying wire until the midpoint has a deflection of 0.30 + 0.05 inch with an applied side load of 20 pounds. \n\n\t3.\tAction Required If The Spar Is Not Cracked \n\t\tReattach the flying wires to the horizontal stabilizer and adjust the flying wires in accordance with the Rigging Procedures in Section VII of the Maintenance Manual. Finally, adjust thetension in each wire until the midpoint has a deflection of 0.30 + 0.05 inch with an applied side load of 20 pounds. Continue the Paragraph 1 inspection at intervals not to exceed 500 hours time in service from the last inspection. When horizontal stabilizer assembly P/N 40221-70 is installed, the repetitive inspections may be discontinued. \n\n\tCompliance with the provisions of this AD may be accomplished in an equivalent manner approved by the Chief, Engineering and Manufacturing Branch, FAA, Southern Region. \n\n\tThis amendment is effective February 20, 1980.