SAIB ACE-96-15 —

No. ACE-96-15 December 20, 1996

Published by: FAA, AFS-610, P.O. Box 26460, Oklahoma City, OK 73125 This is issued for informational purposes only and any recommendation for corrective action is not mandatory.

INTRODUCTION: The purpose of this Special Airworthiness Information Bulletin is to advise registered owners of certain de Havilland airplanes of the need to inspect horizontal and vertical stabilizer attachment fittings. This Bulletin is being sent to registered owners of de Havilland models DHC-6-1, -100, -200, and -300 Twin Otter airplanes.

BACKGROUND: The Federal Aviation Administration (FAA) has received service difficulty reports concerning corrosion and cracking of the fuselage horizontal stabilizer rear attachment adapter on airplanes which have been operated in severe environments. Corrosion was found during routine inspection, but the extent of the corrosion was not readily visible. The manufacturer has created a service bulletin to introduce additional inspection procedures to detect corrosion and cracking due to long-term environmental exposure. The FAA policy on aging commuter class airplanes is to eliminate or, in certain instances, to reduce the number of repetitive inspections when improved parts or modifications are available. In this instance, additional inspections have been determined to be most effective in correcting the discrepant condition.

RECOMMENDATION: The FAA is recommending, but not requiring, that: (A) Owners/operators of de Havilland models DHC-6-1, -100, -200, and -300 Twin Otter airplanes perform additional structural inspections in accordance with de Havilland service bulletin no. 6/454, Inspection Part A, to detect corrosion or cracking, and (B) If any corrosion is found as a result of the above Part A inspection, perform additional inspections in accordance with Inspection Part B of bulletin 6/454 within 200 flight hours. (C) If any cracking is found as a result of the above Part A inspection, perform additional inspections in accordance with Inspection Part B of bulletin 6/454 before further flight.

NOTE: Inspection Part A will require approximately 4 workhours to accomplish, and Inspection Part B will require approximately 40 workhours to complete.

FOR FURTHER INFORMATION CONTACT: Federal Aviation Administration, New York Aircraft Certification Office, 10 Fifth St., Third Floor, Valley Stream, NY 11581, Attention: Jon Hjelm, telephone (516) 256-7523, facsimile (516) 568-2716.