December 2, 2004

This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin alerts repair stations, mechanics holding Inspection Authorization, and Principal Maintenance Inspectors in the Flight Standard District Offices, of service difficulties and safety issues associated with certain Marvel Schabler dual venturi type carburetors.

Background

In a recent accident involving a Fairchild M-62A-3 airplane, the primary venturi in the MA4-5 carburetor was dislodged. Investigation revealed fouled plugs, indicating an excessively rich-running engine, and the carburetor was dirty and badly corroded. A 1963 Service Bulletin (Marvel Schebler No. A4-63) recommends replacement of the twopiece venturi with a one-piece design. Airworthiness Directive (AD) 63-22-03 was published to mandate compliance with this Service Bulletin, but the effectivity of this AD did not include this airplane engine combination, and the accident airplane still contained the original two-piece venturi.

Recommendation

We recommend the following actions:

• Determine if the carburetor installed on a given airplane is a Model MA-4-5. If it is a Model MA-4-5, then verify that AD 63-22-03 (Marvel Schebler Service Bulletin A4-63) is incorporated. If you can't determine this, review the service history of the airplane to determine if the carburetor has been overhauled or replaced since 1964.

• If AD 63-22-03 is complied with, or the carburetor has been overhauled or replaced since 1964, then no further action is required.

• If AD 63-22-03 is not complied with, the carburetor has not been overhauled or replaced since 1964, or if you can't determine any of the above, then inspect the integrity of the venturi to ascertain that it is not dislodged from its position. If the venturi has been dislodged, replace it with the one-piece design or a serviceable twopiece design venturi prior to further flight. If the venturi is intact, no further action is required. This inspection should be repeated at each annual inspection.

For Further Information Contact

Richard Simonson, Seattle Aircraft Certification Office, 1601 Lind Ave SW, Renton WA 98055; telephone (425) 917-6507; fax (425) 917-6590; e-mail:richard.simonson@faa.gov