Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
NM-07-31
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: ken.sujishi@faa.gov