AD 61-04-02

61-04-02 DOUGLAS: Amdt. 250 Part 507 Federal Register February 10, 1961. Applies to All DC-6, DC-6A and DC-6B Aircraft; Fuselage Number 1 Up to and Including Fuselage Number 722, Having in Excess of 9,000 Hours' Time in Service.

Compliance required as indicated.

There have been numerous cases reported of spar cap cracking on DC-6 Series aircraft. Cracking usually occurs in spar cap tangs in the area of the Station 60 attachments and progresses chordwise. In addition, service experience has shown that the temporary repair of the above service difficulties per Douglas Rework Drawing 5611387 does not have the service life originally anticipated. As a result of this service experience, the upper and lower, front and center spar caps in the area of wing Station 60, with special attention to the spar cap tangs between wing Stations 55 and 65, must be inspected for cracks as follows:

(a) The upper and lower, front and center spar caps must be inspected within the next 450 hours' time in service unless already accomplished. Aircraft inspected prior to issuance of this AD must also comply with the repetitive inspections rework and/or repairs specified in (b), (c), (d), and (e).

(b) The upper front and center spar caps on all DC-6, DC-6A, and DC-6B aircraft, Fuselage Nos. 1 through 722, must be reinspected at intervals not to exceed 1,600 hours' time in service.

(c) The lower front and center spar caps must be reinspected as follows:

(1) Model DC-6 aircraft, Fuselage Nos. 1 through 172, which have not been reworked in accordance with DC-6 Service Bulletin Nos. 569 and 724, at intervals not to exceed 1,600 hours' time in service.

(2) Model DC-6 aircraft, Fuselage Nos. 1 through 172, which have been reworked in accordance with DC-6 Service Bulletin Nos. 569 and 724, at intervals not to exceed 3,250 hours' time in service.

(3) Model DC-6, DC-6A and DC-6B aircraft, Fuselage Nos. 174 through 722, at intervals not to exceed 3,250hours' time in service.

(d) If cracks are found, FAA approved permanent rework or temporary repair as recommended by the manufacturer or FAA approved equivalent is required prior to further flight except ferry flight in accordance with the provisions of CAR 1.76. Temporary repairs may be made per Douglas Rework Drawing 5611387, or FAA approved equivalent, providing crack limitations as established on this drawing have not been exceeded.

(e) Aircraft incorporating a temporary repair must be reinspected at intervals not to exceed 750 hours' time in service pending the accomplishment of the FAA approved manufacturer's recommended permanent rework or FAA approved equivalent. Such rework or equivalent must be accomplished within 4,200 hours' time in service after incorporating the temporary repair.

(f) The inspections required by this AD may be discontinued for any area reworked in accordance with FAA approved permanent repair instructions.

(Douglas Alert Service Bulletin A-678 revised June 3, 1960, covers this subject.)

This supersedes AD 60-15-01.

This directive effective March 14, 1961.