74-05-04 MCDONNELL DOUGLAS: Amdt. 39-1793. Applies to all Douglas Aircraft Company DC-10-10 series airplanes. \n\n\tCompliance required within 300 hours additional time in service after the effective date of this airworthiness directive, unless previously accomplished. \n\n\t(1)\tInspect all DC-10-10 airplanes to determine if a yaw computer Part No. 1954094-6 is installed. Remove the inoperative placard from the yaw damper test function on the overhead test panel, if installed. \n\n\t(2)\tIf yaw computer Part No. 1954094-6 is installed in either or both positions, install, prior to further flight, the following placards for the yaw damper test function: \n\n\t\t(a)\t"INOP" on each "YAW DAMP TEST FAIL" light. \n\n\t\t(b)\t"SEE AFM FOR TEST PROCEDURE" to the left on the word "TEST" on the overhead yaw damper panel. \n\n\t(3)\tIncorporate the following limitation and procedure in the DC-10-10 FAA Approved Airplane Flight Manual for the use of the flight crew. An alternate test procedure may be substituted upon submission of adequate substantiating data to the Chief, Aircraft Engineering Division, FAA Western Region, and the receipt of an approval of the alternate procedure from the Chief. \n\n\tIncorporate revisions in the FAA Approved Airplane Flight Manual Documents No. MDC J1010 or MDC J1010, Appendix X, as follows: \n\n\t\t(a)\tRevise existing paragraph heading in Section I, Limitations, to read: YAW DAMPER \n\n\tAny two channels must be operating prior to the start of takeoff. (See yaw damper computer Part No. 1954094-6 test procedure in Section III of FAA Approved Airplane Flight Manual.) \n\n\t\t(b)\tIncorporate the following heading in Section III of FAA Approved Airplane Flight Manual Document No. MDC J1010 or MDC J1010, Appendix X, to read: \n\n\tTEST PROCEDURE FOR YAW DAMPER COMPUTER PART NO. 1954094-6 INSTALLED IN EITHER OR BOTH POSITIONS \n\n\tDuring taxi: \n\n\t(1)\tPlace all four (upper and lower) yaw damper switches ON. \n\n\t(2)\tCenter rudder indices in the surface position indicator with the rudder pedals. \n\n\t(3)\tWhen entering a turn, using primary nose wheel steering, observe the surface position indicator and note that the rudder position indices deflect to the first vertical mark opposite to the direction of turn. \n\n\t-Any rudder surface (position indicator) with only one yaw one yaw damper operative will deflect only one half the rudder deflection noted with two yaw dampers operative. \n\n\t(4)\tIf this test indicates inoperative yaw damper(s), the yaw damper(s) associated with the failed system (upper or lower) must be switched OFF. \n\n\tThis amendment becomes effective March 6, 1974.