AD 90-24-10 ACTIVE

90-24-10 BOEING OF CANADA, LTD., DE HAVILLAND DIVISION: Amendment 39- 6813. Docket No. 90-NM-14-AD.

Applicability: Model DHC-7 series airplanes, Serial Numbers 1 through 10, and 12 through 27, certificated in any category.

Compliance: Required as indicated, unless previously accomplished.

To prevent corrosion and reduced structural capability of the wings accomplish the following:

A. Within 180 days after the effective date of this AD, and thereafter at intervals not to exceed one year, perform a low frequency eddy current inspection of the inboard and outboard fuel tank lower wing skins in accordance with the procedure specified in Part 6, Chapter 57-10- 01, of the de Havilland DHC-7 Nondestructive Testing (NDT) Manual, PSM 1-7-7A.

B. If corrosion is found as a result of the inspections required by paragraph A. of this AD, accomplish the following. Accomplishment of these actions constitutes terminating action for the repetitive inspections of the inboard and/or outboard fuel tank area, as appropriate, required by paragraph A. of this AD.

1. If corrosion is found in the inboard fuel tank, prior to further flight, permanently remove the inboard fuel tank foam blocks, restore any corroded areas, and modify the stringers in accordance with the Accomplishment Instructions, Steps 3, 4, and 5, of de Havilland Service Bulletin 7-57-33, dated July 21, 1989.

2. If corrosion is found in the outboard fuel tank, prior to further flight, permanently remove the outboard fuel tank foam blocks, restore any corroded areas, and modify the stringers in accordance with the Accomplishment Instructions, Steps 3, 4, and 5, of de Havilland Service Bulletin 7-57-33, dated July 21, 1989.

C. If no corrosion is found, within three years after the effective date of this AD, permanently remove the inboard fuel tank foam blocks and modify the stringers in accordance with the Accomplishment Instructions, Steps 3 and 5, of de Havilland Service Bulletin 7-57-33 (), dated July 21, 1989.

D. Accomplishment of the removal and modification actions specified in paragraph C. of this AD, constitutes terminating action for the repetitive inspections of the inboard fuel tank lower wing skins required by paragraph A. of this AD.

E. Accomplishment of the removal and modification actions specified in the Accomplishment Instructions, Steps 3 and 5, of de Havilland Service Bulletin 7-57-33 (), dated July 21, 1989, for the outboard fuel tanks, constitutes terminating action for the repetitive inspections of the outboard fuel tank lower wing skin required by paragraph A. of this AD.

F. An alternate means of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, New York Aircraft Certification Office (ACO), FAA, New England Region.

NOTE: The request should be submitted directly to the Manager, New York ACO, and a copy sent to the cognizant FAA Principal Inspector (PI). The PI will then forward comments or concurrence to the Manager, New York ACO.

G. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD.

All persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to Boeing of Canada, Ltd., de Havilland Division, Garratt Boulevard, Downsview, Ontario M3K 1Y5, Canada. These documents may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue S.W., Renton, Washington, or at the FAA New England Region, New York Aircraft Certification Office, 181 South Franklin Avenue, Room 202, Valley Stream, New York.

This amendment (39-6813, AD 90-24-10) becomes effective on December 24, 1990.