Summary
The FAA proposes to supersede Airworthiness Directive (AD) 2003-21-07, which applies to certain The Cessna Aircraft Company (Cessna) Model 525 airplanes. AD 2003-21-07 currently requires you to disengage the pitch trim circuit breaker and AP servo circuit breaker and then tie strap each of them to prevent them from being engaged. Not utilizing this equipment prevents a single-point failure. This proposed AD is the result of Cessna having now developed and made changes in the design of the affected trim printed circuit board (PCB) assembly to allow the use of the assembly and the prevention of the single-point failure, and identification of additional airplanes that have the same unsafe condition. Consequently, this proposed AD would require you to remove and replace an old trim PCB assembly with a new design assembly or modify an old trim PCB assembly to the new design. We are issuing this proposed AD to correct this single-point failure in the electric pitch trim system, which will result in a runaway pitch trim condition where the pilot could not disconnect using the control wheel autopilot/trim disconnect switch. Failure of the electric trim system would result in a large pitch mistrim and would cause excessive control forces that the pilot could not overcome.