AD 83-21-02 R1

83-21-02 R1 BOEING: Amendment 39-4745 as amended by Amendment 39-5215. Applies to those Model 747 series airplanes certificated in all categories listed in Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision. To prevent failure of the trailing edge flap tracks, accomplish the following:

A. Inspect the external surface of the trailing edge flap tracks visually for cracks or corrosion penetration within the threshold landings set forth in Table I after the effective date of this AD, and thereafter at the repetitive intervals not to exceed those shown in Table I, below, in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision. These external visual inspections are to continue until the modifications of paragraph D are accomplished.

TABLE I

EFFECTIVITY AIRPLANE LINE NO. THRESHOLD FOR INITIAL INSPECTIONS

REPETITIVE INSPECTION INTERVALS

During the initial 250 landings after effective date of the AD. During the 251 thru 500 landings after the effective date of the AD. 001-400 (Group I) 50 Landings 50 Landings 30 Landings 401-584 (Group II) 100 Landings 100 Landings 100 Landings

B. If any cracks are found in any flap track, replace the cracked track before further flight. This replacement criterion applies to all future inspections required by this AD.

C. If any corrosion pits, which have completely penetrated the track web, are visible on the outside of any track web, perform a repeat visual external inspection for cracks in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision, at intervals not exceeding 30 landings. Replace the track within 200 landings after discovery of the corrosion pits, or before further flight if a crack is found. These replacement criteria apply to all future inspections required by this AD.

D. If there are not visible track webcracks and no corrosion pits through either web, modify by drilling the 5/8-inch diameter drain holes in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA approved revision, within 500 landings or six months after the effective date of this AD, whichever occurs first. Flush the track cavity per instructions in the Service Bulletin.

NOTE: Airplane Flap Tracks previously modified by a single 3/8-inch diameter drain hole must still be modified in accordance with the requirements of this paragraph.

E. Concurrent with the modifications of paragraph D., above, perform an internal borescope inspection of the flaptrack in accordance with procedures defined in Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA-approved revision, to determine if corrosion exists. If corrosion or pitting is found, determine its extent by accomplishing the track web X-ray inspection specified in the service bulletin.

1. Perform repeat externalinspections for cracks or corrosion penetration through track webs at the intervals shown in the following Table II:

TABLE II

Maximum Flap Setting Used for landings Internal Corrosion Classification (b) Maximum External Inspection Intervals (Landings) Visual Inspection Magnetic Particle or Penetrant Inspection

25 degrees(a) Heavy 200 250

Moderate 400 450

Light 800 850 30 degrees Heavy 50 65

Moderate 100 115

Light 250 265

(a) Quadrant and alternate extension system must be modified to block off selection of flaps 30 degrees.

(b) Classification terms are defined in Paragraph G. of the Accomplishment Instructions of the referenced service bulletin.

F. Repeat the X-ray inspection specified in paragraph E., above, in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1, or later FAA-approved revision, on tracks indicating medium or light internal web corrosion at intervals not exceeding one year or until heavy web corrosion is indicated, whichever occurs first. This twelve month inspection interval may be extended to fifteen months, provided a monthly repeat visual inspection is initiated at the twelfth month and continued until the X-ray inspection is accomplished. When the classification of the internal corrosion changes then the inspection interval changes as indicated in paragraph E.1., above. If the previous two X-ray inspections show that corrosion progression has been arrested, the X-ray reinspection interval may be increased from 12 to 24 months until subsequent X-ray inspections indicate noticeable corrosion progression. At that time, the interval for X-ray inspection shall revert to 12 months.

G. Apply organic corrosion inhibitor (BMS 3-23 or equivalent) to the aft cavity of each flap track after the borescope inspection of paragraph E. and at intervals not exceeding 6 months in accordance with Boeing Alert Service Bulletin 747-57A2225, Revision 1,or later FAA approved revision.

H. For purposes of complying with this AD, subject to acceptance by the assigned FAA Principal Maintenance Inspector, the number of landings may be determined by dividing each airplane's hours time in service by the operator's fleet average from takeoff to landing for the airplane type.

I. Upon request of the operator, a FAA Principal Maintenance Inspector, subject to prior approval by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region, may adjust the inspection interval, if the request contains substantiating data to justify the increase for that operator.

J. Special flight permits may be issued in accordance with Section 21.197 and 21.199 of the Federal Aviation Regulations to operate airplanes to a base for the accomplishment of the inspections and/or modifications required by the AD.

K. Alternate means of compliance or other actions which provide an equivalent level of safety may be used when approved by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region.

All persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to the Boeing Commercial Airplane Company, P.O. Box 3707, Seattle, Washington 98124-2207. These documents may be examined at the FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or the Seattle Aircraft Certification Office, 9010 East Marginal Way South, Seattle, Washington.

Amendment 39-4745 became effective October 27, 1983. This Amendment 39-5215 becomes effective February 24, 1986.