AD 80-03-08

80-03-08 DeHAVILLAND: Amendment 39-3682. Applies to all DHC-6 model airplanes, certificated in all categories.

To prevent possible asymmetric failure of the flap system due to cracking in the flap control rod tubes, accomplish the following:

1. On aircraft Serial Numbers 1 thru 427, within the next 20 hours in service or 30 days, whichever occurs first, after the effective date of this AD, unless previously accomplished within the last 180 hours in service or 60 days, whichever occurred last, visually inspect the tube ends of the rod assemblies, P/N's C6CW 1029-1, C6CW 1051-1 or C6CW 1024-1, and C6CF 1085-1 or -3, with a dye penetrant method using at least a ten power glass. (See WARNING on page 4 of DeHavilland Service Bulletin 6/388, paragraph 4. and paragraphs 5. and 6. of ACCOMPLISHMENT INSTRUCTIONS.)

2. If cracks are found, the rod assembly must be replaced before further flight with rods of the same part number or equivalent inspected and found serviceable in accordance with paragraph 1; or with new rods with the same part number or equivalent; or with new Post-Mod 6/1487 rods, incorporating EO 66818; or Mod 6/1710 and 6/1714 whose part numbers are listed in DeHavilland Service Bullet in No. 6/388, Table I.

3. If cracks are not found, repeat inspection in paragraph 1. within 200 hours in service or 90 days, whichever occurs first, and install flap control rod sleeves in accordance with Service Bulletin 6/388, ACCOMPLISHMENT INSTRUCTIONS, or approved equivalent. Following the installation of sleeves visually inspect using at least a ten power glass, in accordance with Service Bulletin 6/388, Page 9, Figure 1, at intervals not to exceed 400 hours in service or 90 days, whichever occurs first.

4. On aircraft Serial Numbers 1 thru 427, within 1600 hours in service or two years, whichever occurs first, from the effective date of this AD, unless previously accomplished, replace flap control rods listed in column entitled "Pre-Mod 6/1487" with the appropriate rods from the columns entitled "Retrofit Post-Mod 6/1487 Incorp. Mod 6/1710 and 6/1714" or "Post- Mod 6/1710 and 6/1714, New Product Rods", in Service Bulletin 6/388, Table I. Following the replacement, inspect in accordance with requirements in paragraph 6.

5. On aircraft Serial Numbers 428 thru 656 and aircraft Serial Numbers 1 thru 427 incorporating Post-Mod 6/1487 control rods, inspect rod ends in accordance with method in paragraph 1. and accomplish Mod 6/1710 and 6/1714 in accordance with Service Bulletin 6/388 ACCOMPLISHMENT INSTRUCTIONS, or approved equivalent, no later than 800 hours in service or one year, whichever occurs first, from the last inspection. Following the modifications, inspect in accordance with requirements in paragraph 6.

6. On aircraft Serial Numbers 657 and subsequent, visually inspect control rods using at least a ten power glass, in accordance with Service Bulletin 6/388, Page 9, Figure 1, at intervals not to exceed 800 hours in service or one year, whichever occurs first.

7. Report positive findings, including crack length, from any of the above inspections, to the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region, within 10 days of inspection. (Reporting approved by Office of Management and Budget under OMB No. 04-R0174.)

8. Equivalent parts and procedures must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region.

9. Compliance times may be increased by the Chief, Engineering and Manufacturing Branch, FAA, Eastern Region, upon receipt of substantiating data submitted through an FAA Maintenance Inspector.

NOTE: DeHavilland Service Bulletin 6/388, can be referred to for Inspection and Replacement Instructions pertaining to this subject.

This Directive supersedes Airworthiness Directive 79-10-07.

This amendment is effective February 7, 1980.