77-17-11 BOEING: Amendment 39-3025 as amended by amendment 39-3392. Applies to all B-17F & G airplanes certified in all categories.
Compliance required within the next 25 hours' time-in-service or within 6 months after the effective date of this AD, whichever comes first, unless already accomplished within the last 25 hours time in service or 6 months, and thereafter at intervals not to exceed 50 hours time in service or 12 months, whichever comes first, (from the last inspection).
To detect cracking in the rear spar lower cap center section, P/N 75-3425-2 or 85-3425-2, accomplish the following:
1. Remove the 3 most inboard bolts from the 14 bolt pattern attaching the rear spar center section lower chord P/N 75-3425-2 or 85-3425-2 to the terminal plates, left and right hand sides. These bolts are approximately 40 to 42 inches from the airplane centerline. Using eddy current inspection procedures or boroscope methods in conjunction with dye penetrants, inspect the rear spar lower chord center section for cracks around the bolt holes in both the forward and aft walls of the tube.
2. If cracks are found, replace the spar cap with a serviceable part of the same part number, or repair in accordance with Army T.O. No. 01-20E or other methods approved by the Chief, Engineering and Manufacturing Branch, FAA Northwest Region.
3. After repairs per (2) have been accomplished, reinspect in accordance with (1) at intervals not to exceed 150 hours time-in-service or every 12 months, whichever comes first.
4. The bolt holes described in paragraph (1) above may be reamed .063 inch oversize for a close tolerance oversize bolt, provided no cracks are detected when the chords are inspected in accordance with paragraph (1) above using the eddy current inspection methods. Any holes reworked with the oversize bolts must be reinspected in accordance with (1) above within 1500 flight hours after such rework. Upon accumulation of 1500 flight hours on the reworked holes, the repeat inspection interval reverts to the interval specified in (3) above.
5. Any new replacement beam chords must be inspected within 2500 flight hours after installation and thereafter at intervals specified in paragraph (3) above.
Amendment 39-3025 became effective September 6, 1977.
This amendment 39-3392 becomes effective January 23, 1979.