2004-14-20 THE CESSNA AIRCRAFT COMPANY: Amendment 39-13729; Docket No. 2003-CE-54-AD; Supersedes AD 2003-21-07; Amendment 39-13342.

Airworthiness Directives; The Cessna Aircraft Company Model 525 Airplanes

SUMMARY: The FAA supersedes 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 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 AD requires 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 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.

When Does This AD Become Effective?
   (a)     This AD becomes effective on August 23, 2004.

What Other ADs Are Affected by This Action?
   (b)     This AD supersedes AD 2003-21-07.

What Airplanes Are Affected by This AD?
   (c)     This AD affects Model 525 airplanes with the following serial numbers that are certificated in any category:
    (1)     Group 1 (maintains the actions from AD 2003-21-07): 525-0001, 525-0002, and 525-0004 through 525-0159.
    (2)     Group 2: 525-0160 through 525-0359.

What Is the Unsafe Condition Presented in This AD?
(d)    This 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. The actions specified in this AD are intended 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.