AD FAA-2012-1225

We are adopting a new airworthiness directive (AD) for certain Gulfstream Aerospace Corporation Model GIV-X airplanes. This AD requires performing a modified system power-on self test (SPOST) of the flap/stabilizer electronic control unit (FSECU), and revising the airplane flight manual to incorporate these test procedures into the daily preflight check. This AD was prompted by reports indicating that the FSECU does not detect failures of the brake feature within the horizontal stabilizer electric motor unit (HSEMU), or failures of drive solenoids for hydraulic valves within the flap hydraulic control module (FHCM) during the SPOST. We are issuing this AD to detect and correct such failures, which could result in runaway horizontal stabilizer pitch trim system and consequent loss of pitch control.