Rigid hydraulic case drain lines

FAA Aircraft Certification Service SPECIAL AIRWORTHINESS INFORMATION BULLETIN http://www.faa.gov/aircraft/safety/alerts/SAIB

SAIB: NM-07-31 Date: April 24, 2007 This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin (SAIB) alerts owners, and operators of McDonnell Douglas Corporation Model MD-11 and MD-11F aircraft with CF6-80C2 engines that have rigid hydraulic case drain lines installed. The case drain line can inadvertently be bent during hydraulic pump removal, lose its alignment during pump installation and impose a pre-load condition that can result in subsequent hydraulic fluid leakage in flight. ROHR Inc., a subsidiary of Goodrich Company, has issued a service bulletin to provide instructions to remove and replace the upper and lower rigid case drain lines with flexible hose case drain lines. The service bulletin can be obtained by calling Goodrich Communications Center at 1-619-691-2006.

Background

Operators have experienced unexpected failures of aircraft hydraulic systems. These failures can be attributed to incorrect maintenance procedures that cause a pre-load condition on hydraulic case drain lines and subsequent hydraulic fluid leakage in flight. The MD-11 airplane is designed with three independent hydraulic systems such that all critical hydraulically powered systems can still be operated with any two of the three hydraulic systems failed. This type of an event would be considered a Hazard Class IV event and does not present an airplane level safety threat.

Recommendations

We recommend accomplishment of ROHR Inc. Service Bulletin MD11/80C2-NAC-29-30, entitled Hydraulic-Replacement of hydraulic case drain lines with flexible hose/tube case drain lines (Revision 1, dated July 24, 2002), concerning in service experience with prior (production) configurations.

For Further Information, Contact

Ken Sujishi, Aerospace Engineer, Los Angeles Aircraft Certification Office, ANM-150L, 3960 Paramount Blvd, Lakewood CA 90712; phone: (562) 627-5353; fax: (562) 627-5210 email: [email protected]