This bulletin provides information informing flight crews of temporary recommended procedures in the event of uncommanded autopilot engagement or autoflight mode changes.
Boeing flight tests have encountered a condition that can cause uncommanded autopilot engagement or mode changes of the autopilot or flight director. This condition may occur at any time or altitude except when multiple autopilots are engaged for approach.
This condition is caused by faulty Mode Control Panel pushbutton switches installed during production or repair. The condition affects the left and center Flight Control Computers. These Flight Control Computers normally provide commands for the left and center autopilots and flight directors.
The normal means for disconnecting the autopilot (autopilot disengage switch, autopilot disengage bar, and control wheel stabilizer trim switches) are not affected by this problem.
Boeing and Collins are working aggressively to facilitate the modification of affected units by mid summer, 1993. To date, no in service events have been reported to Boeing.
Flight crews should be prepared to disengage the autopilot during critical phases of flight including takeoff. Flight Mode Displays must be closely monitored. An uncommanded mode change or autopilot engagement can be corrected by selecting the desired mode or disconnecting the autopilot.
This Operations Manual Bulletin will be canceled after Boeing is notified that all affected airplanes in the operators fleet have been modified by Collins Component Service Bulletin MCP-701-22-19, dated April 23, 1993 or Collins Component Service Bulletin MCP-704-22-10, dated April 23, 1993. Additional details and specific applicability of the Service Bulletins are contained in Boeing All-operator telex M-7272-93-2738, dated May 10, 1993.