AD 53-26-01

53-26-01 BRIGGS AND STRATTON: Applies to All Airplanes Equipped With AAF Type B-5 Ignition Switch Manufactured by Briggs and Stratton. Affected Airplanes Include Beech Models D18S (Serial Numbers A-1 Through A-537), D18C, D18C-T, C18S and AT-11 Having the AAF Type B-5 Briggs and Stratton Switch Installed.

Compliance required not later than April 1, 1954.

Design of the Briggs and Stratton AAF Type B-5 switch will permit foreign objects to enter the master ignition switch portion of the switch assembly. As a result, the magnetos of both engines connected to the switch may accidentally become grounded. Gaps in the enclosure of the Briggs and Stratton master switch can allow entry of foreign objects; whereas, AAF Type B-5 switches produced by other manufacturers are tightly sealed. These latter switches are not considered hazardous.

Briggs and Stratton AAF Type B-5 switches are identified by:

(1) The letters "AAF TYPE B-5" on the face of the switch and

(2)The words "Briggs & Stratton Corp., Milwaukee, Wis., U.S.A." stamped on the master switch enclosure. Determination of whether the switch carries the designation of (2) will probably necessitate examination with a flashlight and mirror or removal of the switch from its mount in the airplane.

If AAF Type B-5 switches manufactured by Briggs and Stratton are installed, accomplish either of the following:

(a) Replace the Briggs and Stratton AAF Type B-5 switch with a Type B-5 switch having the master ignition switch portion adequately sealed against entry of foreign objects.

(b) Remove the master ignition and battery switch portion of the Briggs and Stratton AAF Type B-5 in the following manner:

1. Remove the switch assembly from its mount on the airplane.

2. Drill out the three rivets attaching the master switch portion to the face plate of the ignition switch assembly.

3. The six electrical wires connecting the master switch portion to the threaded terminals are to be disconnected at the threaded terminals and discarded with the master switch portion.

4. Clean the ignition switch brass ground strip to make a good electrical contact and rivet it to the case with AN rivet.

5. Reinstall the modified Type B-5 ignition switch assembly in the airplane. Minor rework of the airplane electrical system may be required if the electrical master switch was connected through the Type B-5 master ignition and battery switch.

NOTE: Proper precautions should be observed when the ignition switch is removed or disconnected since the engine magnetos are not grounded.

(Beech Service Bulletin; Model D18S, D-18C, D-18C-T, C18S, AT-11; No. 64, issued November 10, 1953, covers this same subject.)