Airworthiness Directive · Amendment 39-15003 · Boeing Model 747 Airplanes
Boeing Model 747 Airplanes
Superseded. A later AD replaced this one: AD 2021-07-09. Comply with the one in force.
This AD applies to Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 747SP series airplanes; certificated in any category; line numbers 1 through 1316 inclusive.
The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 747 airplanes. This AD requires repetitive tests to detect hot air leaking from the trim air diffuser ducts or sidewall riser duct assemblies (collectively referred to in this AD as "TADDs"), related investigative actions, and corrective actions if necessary. This AD also provides an optional terminating action for the repetitive tests. This AD results from reports of sealant deteriorating on the outside of the center wing fuel tank and analysis that sealant may deteriorate inside the tank due to excess heat from leaking TADDs. We are issuing this AD to prevent leakage of fuel or fuel vapors into areas where ignition sources may be present, which could result in a fire or explosion.
You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.
Do the actions in Table 1 of this AD at the times specified in Table 1 of this AD, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 747-21A2418, Revision 4, dated November 17, 2005. When the compliance times for a hot air leak test and a general visual inspection coincide, the hot air leak test is not required at that time, but is required within 1,200 flight hours (i.e., one repeat interval) after the general visual inspection.
| Do this action— | Initially at the later of— | Then repeat within this interval until paragraph (j) is done— |
|---|---|---|
| (1) Repetitive test to detect hot air leaking from TADDs. | Prior to the accumulation of 21,200 total flight hours, or within 1,200 flight hours after the effective date of this AD | 1,200 flight hours. |
| (2) General visual inspection for damage or discrepancies of the TADDs | Prior to the accumulation of 32,000 total flight hours, or within 12,000 flight hours after the effective date of this AD, except as provided by paragraph (g) of this AD | 12,000 flight hours. |
Note 1: For the purposes of this AD, a general visual inspection is: “A visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure, or irregularity. This level of inspection is made from within touching distance unless otherwise specified. A mirror may be necessary to ensure visual access to all surfaces in the inspection area. This level of inspection is made under normally available lighting conditions such as daylight, hangar lighting, flashlight, or droplight and may require removal or opening of access panels or doors. Stands, ladders, or platforms may be required to gain proximity to the area being checked.”
Note 2: Boeing Service Bulletin 747-21A2418, Revision 4, refers to Chapters 21-61-20 and 21-61-21 of the Boeing 747 Airplane Maintenance Manual as an additional source for service information for the test and inspections of the TADDs.
(g) If any hot air leak is found during any test required by paragraph (f) of this AD: Before further flight, do the general visual inspection for damage or discrepancies of the TADDs, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 747-21A2418, Revision 4, dated November 17, 2005.
If any damage or discrepancy is found during any general visual inspection for damage required by paragraph (f) or (g) of this AD: Do the actions in paragraphs (h)(1), (h)(2), (h)(3), and (h)(4) of this AD, as applicable. Do all of these actions in accordance with the Accomplishment Instructions of Boeing Service Bulletin 747-21A2418, Revision 4, dated November 17, 2005.
(1) Before further flight: Perform a general visual inspection for damage of the primary and secondary fuel barriers of the center wing tank; structure adjacent to the discrepant TADD; and cables, cable pulleys, and raised cable seals in the over-wing area. If no damage is found on the side of the airplane where the damaged or discrepant TADD is found, inspecting the other side of the airplane is not required.
(2) Before further flight: Repair all damage or discrepancies found.
(3) Before further flight: Replace any damaged TADD with a new TADD having the same part number or a new or serviceable, improved TADD having a part number listed in the “New TADD Part Number” or “New Sidewall Riser Duct Assy Part Number” column, as applicable, of the tables in Section 2.C.2. of the service bulletin.
(4) Repeat the test and inspection required by paragraph (f) of this AD at the times specified in Table 1 of this AD, except as provided by paragraphs (i) and (j) of this AD.
(i) For any original-material TADD that is replaced with a new TADD having the same part number as the TADD being replaced: Within 21,200 flight hours after the TADD is replaced, do the test to detect hot air leaking from the replaced TADD, and within 32,000 flight hours after the TADD is replaced, do the general visual inspection for damage, as specified in paragraph (f) of this AD. Thereafter, repeat the test and inspection at the repetitive intervals specified in Table 1 of this AD, except when the times for a hot air leak test and a general visual inspection coincide, the leak test is not required.
Replacing existing TADDs with new or serviceable, improved TADDs terminates repetitive test and inspection requirements as specified in paragraphs (j)(1), (j)(2), and (j)(3) of this AD. New or serviceable, improved TADDs are those having a part number listed in the “New TADD Part Number” or “New Sidewall Riser Duct Assy Part Number” column, as applicable, of the tables in Section 2.C.2. of Boeing Service Bulletin 747-21A2418, Revision 3, dated December 21, 2004; or Revision 4, dated November 17, 2005.
(1) The repetitive general visual inspections required by paragraph (f)(2) of this AD are terminated for each TADD that is replaced with a new or serviceable, improved TADD.
(2) Replacing all TADDs on one side of the airplane with new or serviceable, improved TADDs terminates all repetitive tests required by paragraph (f)(1) of this AD and all repetitive inspections required by paragraph (f)(2) of this AD only for the side of the airplane on which the improved TADDs are installed.
(3) Replacing all TADDs on both sides of the airplane with new or serviceable, improved TADDs terminates all repetitive tests required by paragraph (f)(1) of this AD and all repetitive inspections required by paragraph (f)(2) of this AD.
Actions done before the effective date of this AD in accordance with Boeing Alert Service Bulletin 747-21A2418, dated November 14, 2002; Revision 1, dated October 16, 2003; Revision 2, dated March 4, 2004; or Boeing Service Bulletin 747-21A2418, Revision 3, dated December 21, 2004; are acceptable for compliance with the corresponding actions required by this AD.
