Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
NM-16-24
September 15, 2016
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin is to advise owners and
operators of the potential for skin corrosion under the external oxygen
line fairing located on the top aft section of the fuselage, on Learjet
Inc. Model 25, 25A, 25B, 25C, 25D, 25F, 28, 29, 31, 31A, 35, 35A
(C-21A), 36, 36A, 55, 55B, and 55C 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
We have received reports of skin corrosion found under the external
oxygen line fairing located on the top aft section of the fuselage of
certain Learjet Inc. Model 35 airplanes. The external oxygen line
provides oxygen from the oxygen bottle located in the dorsal fin to the
occupants in the cabin. Airplanes with the oxygen tank mounted in the
dorsal fin will have the external oxygen line on top of the fuselage
covered by a fairing. Airplanes that retain the oxygen line fairing on
top of the fuselage, even though the oxygen bottles have been removed
from the dorsal fin, are also affected. Removal of the fairing, oxygen
line and supporting brackets is necessary to detect the full extent of
fuselage skin corrosion. The same oxygen line fairing design is
installed on the other airplane models identified above.
The FAA recommends that owners/operators of the affected airplanes accomplish the following service information:
Learjet 25 Service Bulletin SB 25-53-4 dated November 23, 2015,
Revision 1, dated April 4, 2016, or Revision 2, April 18, 2016 (or
later approved revisions) “Fuselage – Inspection of Upper Fuselage Skin
under the Aft Oxygen Line Fairing”
Learjet 28/29 Service Bulletin SB 28/29-53-4 dated November 23, 2015,
Revision 1, dated April 4, 2016, or Revision 2, dated April 18, 2016
(or later approved revisions) “Fuselage – Inspection of Upper Fuselage
Skin under the Aft Oxygen Line Fairing”
Learjet 31 Service Bulletin SB 31-53-12 dated November 23, 2015,
Revision 1, dated April 4, 2016, or Revision 2, dated April 18, 2016
(or later approved revisions) “Fuselage – Inspection of Upper Fuselage
Skin under the Aft Oxygen Line Fairing”
Learjet 35/36 Service Bulletin SB 35/36-53-15 dated November 23, 2015,
Revision 1, dated April 4, 2016, or Revision 2, dated April 18, 2016
(or later approved revisions) “Fuselage – Inspection of Upper Fuselage
Skin under the Aft Oxygen Line Fairing”
Learjet 55 Service Bulletin SB 55-53-13 dated November 23, 2015,
Revision 1, dated April 4, 2016, or Revision 2, dated April 18, 2016
(or later approved revisions) “Fuselage – Inspection of Upper Fuselage
Skin under the Aft Oxygen Line Fairing”
We also recommend that owners and operators report the results of each
inspection to Learjet (even if no corrosion is found) using the
Compliance Response Form in the service bulletins. In addition, if any
of the skin thickness values fall below the minimum thickness table in
Chapter 53 of the Learjet Structural Repair Manual, report the
corrosion details to Learjet Customer Support Engineering or Customer
Response Center (CRC) 1-866-538-1247 (Toll Free) / 1-514-855-2999.
Under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et
seq.), the Office of Management Budget (OMB) has approved the
information contained in this SAIB, and assigned OMB Control Number
2120-0731.
For Further Information Contact
Paul Chapman, Aerospace Engineer, Airframe and Services Branch,
ACE-118W, FAA, Wichita Aircraft Certification Office; 1801 Airport
Road, Room 100, Mid-continent Airport, Wichita, Kansas 67209; phone:
316 946-4152; fax: 316 946-4107; email: paul.chapman@faa.gov.
(Optional) For Related Service Information Contact
Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-2942; telephone
316-946-2000; fax 316-946-2220; email ac.ict@aero.bombardier.com;
Internet http://www.bombardier.com.
