COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 737 Series Aeroplanes AD/B737/48 Rudder Trim 11/90 Applicability: All model 737-300 and 737-400 series. Requirement: 1. Replace the rudder trim control knob with a smooth round fluted knob. 2. If the rudder trim control knob is located near the rear of the cockpit centre console, add a guard rail with a height of approximately 38 mm (1.5 inches) to the rear of the cockpit centre console if no rail is currently installed; or, if a rail is currently installed, raise the cockpit centre console rear rail to a height of approximately 38 mm (1.5 inches). Note: FAA AD 90-14-02 Amdt 39-6644 and Boeing Service Bulletin 737-27-1165 refer. Compliance: Prior to 30 November 1991. Background: This Directive is raised in response to reports of inadvertent rudder trim actuation. This condition could lead to a take-off with an improperly trimmed rudder, and may result in a rejected take-off.