Airworthiness Directive · Amendment 39-11736 · Boeing Model 747-400 Series Airplanes
Boeing Model 747-400 Series Airplanes
Superseded. A later AD replaced this one: AD 2001-18-04. Comply with the one in force.
Model 747-400 series airplanes, line numbers 1 through 1205 inclusive, certificated in any category, and equipped with dual crown skin heat exchangers.
Note 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (c) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.
This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747- 400 series airplanes. This action requires repetitive inspections to detect damage or deflection of the crew rest heat exchanger, and follow-on actions, if necessary. This amendment is prompted by reports of cracking and buckling of the front edge of the crew rest heat exchanger on several airplanes. The actions specified in this AD are intended to detect and correct damage or deflection of the crew rest heat exchanger, which could result in jamming of the rudder or elevator control cables, and consequent reduced controllability of the airplane.
To detect and correct damage or deflection of the crew rest heat exchanger, which could result in jamming of the rudder or elevator control cables, and consequent reduced controllability of the airplane, accomplish the following:
(a) Within 1,200 flight hours or 90 days after the effective date of this AD, whichever occurs first, perform a general visual inspection of the crew rest heat exchanger to detect deflection or damage, in accordance with Boeing Alert Service Bulletin 747-21A2412, dated January 20, 2000. Repeat the inspection thereafter at intervals not to exceed 2,500 flight hours.
Note 2: For the purposes of this AD, a general visual inspection is defined as: “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 under normally available lighting conditions such as daylight, hangar lighting, flashlight, or drop-light, 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.”
(b) If any damage or deflection is detected during any inspection required by paragraph (a) of this AD, prior to further flight, replace the discrepant heat exchanger with a new heat exchanger, and measure the thickness of the material of the discrepant heat exchanger, in accordance with Boeing Alert Service Bulletin 747-21A2412, dated January 20, 2000. If the material is greater than or equal to 0.028 inches thick but less than or equal to 0.038 inches thick (≥ 0.028 but ≤ 0.038 inches thick), send the damaged heat exchanger and inspection results to the Manager of Service Bulletin Engineering, Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124.
Note 3: There is a typographical error in the Accomplishment Instructions on page 10 of the alert service bulletin. Item G. under the heading “Inspection and Replacement of the Heat Exchanger (All Airplanes)” reads, “If the material thickness is between 0.028—0.034 inches[,] send the damaged heat exchanger and your inspection results to Boeing.” The number “0.034” should read “0.038.”
