AD 94-21-05 R1 ACTIVE

This amendment clarifies an existing airworthiness directive (AD), applicable to certain Boeing Model 737-300, -400, and -500 series airplanes, that currently requires modification, adjustments, and tests of the thrust reverser system; and repair, if necessary. This amendment clarifies a requirement specified in the AD concerning the performance of the operational test of the system. This amendment is prompted by an inquiry from an operator of the affected airplanes concerning that aspect of the existing AD. \n\n\tThe incorporation by reference of certain publications listed in the regulations was approved by the Director of the Federal Register as of November 25, 1994 (59 FR 53573, October 25, 1994).

Final rule; correction

94-21-05 R1 BOEING: Amendment 39-9314. Docket 93-NM-122-AD. Revises AD 94-21-05, Amendment 39-9047. \n\n\tApplicability: Model 737-300, -400, and -500 series airplanes equipped with CFM International CFM56-3 series engines, certificated in any category. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent deployment of a thrust reverser in flight and subsequent reduced \nontrollability of the airplane, accomplish the following: \n\n\t(a)\tFor airplanes on which the sync-lock installation (specified in paragraph (b) of this AD), sync-lock wiring modification (specified in paragraph (c) of this AD), or Production Revision Record (PRR) 35105 has not been accomplished: Within 60 days after the effective date of this AD, and thereafter at intervals not to exceed 4,000 hours time-in-service, perform adjustments and tests of the thrust reverser system that are specified in Section 78-31-00 of the Boeing 737 Maintenance Manual to verify proper operationof the thrust reverser system, in accordance with that section of the maintenance manual. If any discrepancy is found, prior to further flight, accomplish either paragraph (a)(1) or (a)(2) of this AD. \n\n\t\t(1)\tRepair any discrepancy found, in accordance with procedures described in the Boeing 737 Maintenance Manual. Or \n\n\t\t(2)\tDeactivate the associated thrust reverser in accordance with the existing provisions and limitations specified in the Master Minimum Equipment List (MMEL). \n\n\t(b)\tFor airplanes on which the sync-lock feature was not installed during production or as a modification in accordance with Boeing Service Bulletin 737-78-1053, dated December 17, 1992: Within 5 years after the effective date of this AD, install an additional thrust reverser system locking feature (sync-lock installation) in accordance with Boeing Service Bulletin 737-78- 1053, Revision 1, dated July 1, 1993; Revision 2, dated February 17, 1994; or Revision 3, dated June 30, 1994. Installation ofthe additional locking feature constitutes terminating action for the tests required by paragraph (a) of this AD. \n\n\t(c)\tFor airplanes listed in Boeing Service Bulletin 737-78-1058, dated July 1, 1993: Within 5 years after the effective date of this AD, modify the sync-lock wiring in accordance with Boeing Service Bulletin 737-78-1058, dated July 1, 1993; Revision 1, dated February 17, 1994; or Revision 2, dated July 7, 1994. Modification of the sync-lock wiring constitutes terminating action for the tests required by paragraph (a) of this AD. \n\n\t(d)\tAt the times specified in paragraph (e) of this AD, accomplish the "Thrust Reverser Sync-Lock Integrity Test" specified below to verify that the sync-locks are not failing in the unlocked state. If any discrepancy is found, prior to further flight, accomplish paragraph (d)(1) or (d)(2) of this AD. \n\n\t\t(1)\tRepair any discrepancy found, in accordance with procedures specified in the Boeing 737 Maintenance Manual. Or \n\n\t\t(2)\tDeactivate the associated thrust reverser in accordance with the existing provisions and limitations specified in the MMEL; and verify that the failed sync-lock is deactivated and in the locked position. \n\n\t\t"THRUST REVERSER SYNC-LOCK INTEGRITY TEST \n1.\tGeneral \n\n\tA.\tUse this procedure to test the integrity of the thrust reverser sync-locks. \n\t\tThe procedure must be performed on each engine. \n\n2.\tThrust Reverser Sync-Lock Test\n \n\tA.\tPrepare for the Thrust Reverser Sync-Lock test. \n\t\t(1)\tDo the steps that follow to supply power to the thrust reverser \n\t\t\tsystem: \n\t\t\t(a)\tMake sure the thrust levers are in the idle position. \n\t\t\t(b)\tMake sure the thrust reversers are retracted and locked. \n\t\t\t(c)\tMake sure these circuit breakers on the P6 circuit breaker \n\t\t\t\tpanel are closed: \n\t\t\t\t1)\tENGINE 1 THRUST REVERSER CONT SYS \n\t\t\t\t2)\tENGINE 2 THRUST REVERSER CONT SYS \n\t\t\t\t3)\tENGINE 2 THRUST REVERSER CONT \n\t\t\t\t\tSYS-ALT \n\t\t\t\t4)\tENGINE 1 THRUST REVERSER IND SYS \n\t\t\t\t5)\tENGINE 2 THRUST REVERSER IND SYS \n\t\t\t\t6)\tENGINE 1 SYNC-LOCK \n\t\t\t\t7)\tENGINE 2 SYNC-LOCK \n\t\t\t\t8)\tENGINE 2 SYNC-LOCK-ALTN \n\t\t\t\t9)\tLANDING GEAR AIR/GND RELAY \n\t\t\t\t\tAND LIGHTS \n\t\t\t\t10)\tRADIO ALTM-2 \n\t\t\t(d)\tMake sure this circuit breaker on the P18 circuit breaker \n\t\t\t\tpanel is closed: \n\t\t\t\t1)\tRADIO ALTM-1 \n\t\t\t(e)\tSupply electrical power. \n\t\t\t(f)\tRemove pressure from the A (for the left engine) or B (for \n\t\t\t\tthe right engine) hydraulic system. \n\n\tB.\tDo the thrust reverser sync-lock test. \n\t\t(1)\tMove and hold the manual unlock lever on the upper actuator on \n\t\t\tboth thrust reverser sleeves to the unlock position. \n\t\t(2)\tMake sure the thrust reverser sleeves did not move aft. \n\t\t(3)\tMove the left (right) reverse thrust lever up and rearward to the \n\t\t\treverse thrust position. \n\t\t(4)\tMake sure both thrust reverser sleeves move aft (approximately \n\t\t\t0.15 to 0.25 inch). \n\t\t(5)\tRelease the manual unlock lever on the upper actuators. \n\n\tWARNING: MAKE SURE ALL PERSONS AND EQUIPMENT ARECLEAR OF THE AREA AROUND THE THRUST REVERSER. WHEN \n\tYOU APPLY HYDRAULIC PRESSURE, THE THRUST REVERSER \n\tWILL EXTEND AND CAN CAUSE INJURIES TO PERSONS OR \n\tDAMAGE TO EQUIPMENT. \n\n\t\t(6)\tPressurize the A (B) hydraulic system. \n\t\t(7)\tMake sure the thrust reverser extends. \n\t\t(8)\tMove the left (right) reverse thrust lever to the forward and down \n\t\t\tposition to retract the thrust reverser. \n\n\tC.\tPut the airplane back to its usual condition. \n\t\t(1)\tRemove hydraulic pressure. \n\t\t(2)\tRemove electrical power. \n\n\tD.\tRepeat the thrust reverser sync-lock test on the other engine." \n\n\t(e)\tAccomplish the test required by paragraph (d) of this AD at the times specified in paragraph (e)(1) or (e)(2) of this AD, as applicable. \n\n\t\t(1)\tFor airplanes that are subject to the requirements of paragraphs (b) and (c) of this AD: Within 4,000 hours time-in-service after accomplishing the modification required by paragraph (b) or (c) of this AD, as applicable, or within 4,000 hours time-in-service after the effective date of this AD, whichever occurs later; and thereafter at intervals not to exceed 4,000 hours time-in-service. \n\n\t\t(2)\tFor all other airplanes: Within 4,000 total hours time-in-service, or within 4,000 hours time-in-service after the effective date of this AD, whichever occurs later; and thereafter at intervals not to exceed 4,000 hours time-in-service. \n\n\t(f)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. \n\n\tNOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\n\t(g)\tSpecial flight permits may beissued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n\t(h)\tThe installation and wiring modification shall be done in accordance with Boeing Service Bulletin 737-78-1053, Revision 1, dated July 1, 1993; Boeing Service Bulletin 737-78- 1053, Revision 2, dated February 17, 1994; Boeing Service Bulletin 737-78-1053, Revision 3, dated June 30, 1994; Boeing Service Bulletin 737-78-1058, dated July 1, 1993; Boeing Service Bulletin 737-78-1058, Revision 1, dated February 17, 1994; or Boeing Service Bulletin 737-78- 1058, Revision 2, dated July 7, 1994. The incorporation by reference of this document was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51 as of November 25, 1994 (59 FR 53573, October 25, 1994). Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707,Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. \n\n\t(i)\tThis amendment is effective on November 25, 1994.

On October 6, 1994, the FAA issued AD 94-21-05, amendment 39-9047 (59 FR 53573, October 25, 1994), applicable to certain Boeing Model 737-300, -400, and -500 series airplanes, to require modification, adjustments, and tests of the thrust reverser system; and repair, if necessary. The actions required by that AD are intended to prevent deployment of a thrust reverser in flight and subsequent reduced controllability of the airplane. \n\n\tSince the issuance of that AD, the FAA has received an inquiry from an operator of the affected airplanes concerning the requirement of paragraph (d)(2) of the AD. That paragraph requires deactivation of a thrust reverser if a discrepancy is found during accomplishment of the thrust reverser sync-lock integrity test. The last sentence of paragraph (d)(2) specifies that, following deactivation of the associated thrust reverser, "the sync-locks installed on the deactivated thrust reverser must remain operational." The operator questions how the sync-lock can remain "operational" when the thrust reverser has been deactivated for failing the required integrity test. \n\n\tThe FAA finds that clarification of the term "operational" is necessary. The FAA's intent in specifying that the sync-lock remain operational was actually to require that it be verified to be in the locked position. In order to avoid unnecessary flight delays and cancellations, the FAA included the provision contained in paragraph (d)(2) of AD 94-21-05 to provide relief to allow dispatch of the airplane with deactivated sync-locks, in accordance with provisions and limitations contained in the Master Minimum Equipment List (MMEL). This relief involves locking out a thrust reverser and verifying that the failed sync-lock is deactivated and in the locked position. In light of this, action is taken herein to revise AD 94-21-05 to clarify paragraph (d)(2) of the AD accordingly. There are no other changes to the rule. \n\n\tThe final ruleis being reprinted in its entirety for the convenience of affected operators. The effective date remains November 25, 1994. \n\n\tSince this action only clarifies a requirement of a final rule, it has no adverse economic impact and imposes no additional burden on any person. Therefore, notice and public procedures hereon are unnecessary.\n\n List of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. Adoption of the Amendment \n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:\n\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\tThe authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 39.13 - (Amended) \n\n\t2.\tSection 39.13 is amended by removing amendment 39-9047 (59 FR 53573, October 25,1994), and by adding a new airworthiness directive (AD), amendment 39-9314, to read as follows:

The service information referenced in this AD may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Stephen Bray, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2681; fax (206) 227-1181.