Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
NE-08-44
September 3, 2008
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin advises you, registered
owners, operators, and certificated repair facilities of all airplanes
equipped with General Electric Company (GE) CF6-80C2 and CF6-80E1
series turbofan engines of the discovery of substandard clevis pins,
which can be found on thrust reverser actuators and central drive units
(CDUs). There was one event where a translating cowl liberated from its
engine upon thrust reverser deployment. These turbofan engines are
installed on Airbus A300-600/R/F, A310-200/-300, and A330-200/-300
airplanes, Boeing 747-300/-400/-400ER, and
767-200/-200ER/-300/-300ER/-400ER airplanes, and MD-11 airplanes. At
this time, the airworthiness concern is not an unsafe condition that
would warrant airworthiness directive (AD) action under Title 14 of the
Code of Federal Regulations (14 CFR) part 39.
Background
In January 2007, there was a single event in which a non-U.S.
operator’s airplane deployed its thrust reversers on a CF6-80C2
turbofan engine during landing. Upon deployment, the inboard
translating cowl of the thrust reverser separated from the engine. This
caused an uncommanded yaw of the aircraft due to asymmetric thrust.
Also, several pieces of debris were left on the runway from the
translating cowl, which posed a hazard to other aircraft operating on
the runway until the debris was removed.
After inspection, it was determined that a clevis pin, which did not
meet the specifications required for the certified part, was installed.
These clevis pins pass through and secure the translating cowl’s upper
and lower actuators as well as the CDU. The source of the unapproved
pin is undetermined at this time.
The material of the clevis pins approved for use on these thrust
reversers is heat treated, stainless steel, while the material of the
unapproved clevis pin was determined to be a low strength carbon steel,
which was not heat treated. Installation of the unapproved clevis pin
led directly to the failure of the thrust reverser. This failure took
place at an unknown number of cycles after installation.
Recommendations
We recommend inspection of thrust reverser actuator and CDU clevis pins
at the earliest opportunity, to ensure they meet approved
specifications.
Significant surface corrosion is one sign that the pins are made of
carbon steel, as opposed to the approved clevis pins, which are made of
stainless steel. However, corrosion might not be present on carbon
steel pins if they have not yet had enough time in service to corrode.
A rebound hardness test is a more conclusive method to determine
whether a pin was made from low strength carbon steel. The stainless
steel clevis pins should measure between 31-38 HRC (Rockwell Hardness
scale C). Standard carbon steel measures a much lower hardness than
this value.
Performing this test can be accomplished either on-wing with the pins
still installed, or with the pins removed during a shop visit.
Further information on performing a hardness test can be found in GE’s
Standard Practices Manual, GEK 108792, Section 70-34, Hardness
Measurement Procedures. GE Standard Practices Manual, Sections 70-34-03
and 70-34-04 specifically describe how to perform a Rockwell Hardness
Test. The hardness test must be performed on a flat surface on the face
of the pin. Any pin whose hardness does not fall in the range of 31-38
HRC must be considered to be made of an unapproved material, and
therefore, unapproved for service.
General Electric distributed All Operators Wire (AOW), 07/CF6/012,
CF6-80C2 Thrust Reverser Transcowl Liberation Related to a Non-OEM
Part, to all GE CF6 operators on April 10, 2007, which provided
additional relevant information. The AOW contains information including
pin locations and photographs of one unapproved pin from the event
engine compared with an approved pin, which is still in good condition.
Note in the photographs in the AOW that in addition to the difference
in corrosion levels of the pins, the shape of the notch cut in the pins
is different. On the approved pin, the corners at the base of the notch
are rounded, while on the unapproved pin, the corners are sharp.
For Further Information Contact
Christopher J. Richards, Aerospace Engineer, Engine Certification
Office, FAA, Engine and Propeller Directorate, 12 New England Executive
Park, Burlington, MA 01803; e-mail: christopher.j.richards@faa.gov;
phone: (781) 238-7133; fax: (781) 238-7199.
For Related Service Information Contact
General Electric Company, 1 Neumann Way, Cincinnati, OH 45216-6301; phone: (513) 552-3272; fax: (513) 552-3329.