Airworthiness Directive · Amendment 39-16904 · Flight controls
The Boeing Company Airplanes
This AD applies to all Model 737 airplanes; certificated in any category.
We are adopting a new airworthiness directive (AD) for all Model 737 airplanes. This AD was prompted by a report of extensive corrosion of a ballscrew used in the drive mechanism of the horizontal stabilizer trim actuator (HSTA). This AD requires repetitive inspections, lubrications, and repetitive overhauls of the ball nut and ballscrew and attachment (Gimbal) fittings for the trim actuator of the horizontal stabilizer; various modification(s); and corrective actions if necessary; as applicable. We are issuing this AD to prevent an undetected failure of the primary load path for the ballscrew in the drive mechanism of the HSTA and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane.
You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.
At the applicable compliance time and repeat intervals listed in Tables 1 and 2 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; or Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010; as applicable (depending on airplane configuration): Do the inspections, lubrications, overhauls, modification(s), and applicable corrective actions, by accomplishing all the applicable actions specified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; or Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010; as applicable; except as provided by paragraphs (g)(1) and (g)(2) of this AD.
Note 1: Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010; and Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; refer to the following component maintenance manuals (CMMs) as additional sources of guidance for accomplishing the applicable specified actions: Boeing CMM 27-45-11, dated November 1, 2011; Boeing CMM 27-45-12, dated November 1, 2011; Skytronics CMM 27-40-03, Revision 1, dated September 1, 2006; Umbra Cuscinetti CMM 27-41-01, Revision 5, dated September 27, 2005; and Linear Motion CMM 27-41-01, Revision 8, dated May 21, 2008; as applicable.
Note 2: Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010, refers to Umbra Cuscinetti Service Bulletin 07322-27-01, dated December 21, 2004; Linear Motion Service Bulletin 7901708, Revision A, and Revision B, both dated July 26, 2005; Boeing 737 Service Bulletin 27-1046, Revision 1, dated April 5, 1974; and SKYTRONICS Service Bulletin 93004, dated September 1, 2005; as additional sources of guidance for accomplishing the applicable specified actions.
Note 3: Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010, refers to Umbra Cuscinetti Service Bulletin 07322-27-01, dated December 21, 2004, as an additional source of guidance for accomplishing the applicable specified actions.
(1) Where paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; or Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010; as applicable; specifies an initial compliance time for accomplishing the initial inspection, lubrication, overhaul, or modification, this AD requires doing the applicable initial action(s) at the later of the times specified in paragraphs (g)(1)(i) and (g)(1)(ii) of this AD.
(i) At the applicable compliance time specified in paragraph 1.E, “Compliance,” of Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; or Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010; as applicable.
(ii) Within the applicable compliance time specified in paragraph (g)(1)(ii)(A), (g)(1)(ii)(B), or (g)(1)(ii)(C) of this AD.
(A) For the initial detailed inspection and lubrication: Within 6 months after the effective date of this AD.
(B) For the initial overhaul: Within 12 months after the effective date of this AD.
(C) For the modification(s): Within 24 months after the effective date of this AD.
(2) Where Table 2 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010, specifies a compliance time of “* * * within 25,000 Flight Hours since the latest horizontal stabilizer trim actuator (HSTA) Overhaul from the date of Revision 1 of this Service Bulletin * * *,” this AD requires compliance within 25,000 flight hours since the last overhaul of the trim actuator of the horizontal stabilizer.
Actions accomplished before the effective date of this AD in accordance with Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007; or Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007; as applicable; are considered acceptable for compliance with the corresponding actions specified in this AD.
As of the effective date of this AD, no person may install a ballscrew assembly in the drive mechanism of the HSTA on any airplane, unless it has been inspected and modified, as applicable, in accordance with paragraph (g) of this AD.
