Gulfstream Aerospace technicians were responsible for uncovering a preflight systems test malfunction that led to last week’s FAA Airworthiness Directive on all 260 G350/450s. The December 12 directive–2012-NM-219-AD–took effect December 17 and addresses the flap/stabilizer electronic control unit cockpit crewmembers normally test before the first flight of the day.

The test that failed normally confirms the operational readiness of the hydraulic brake used to stop the pitch trim motor in the event of a runaway event. A Gulfstream spokesman told AIN that neither the pitch-trim motor nor the brake itself was in question, only the software used to test the system.

While a software fix is being developed, Gulfstream issued an alert customer bulletin, as well as a maintenance operations letter outlining a manual test procedure that adds a few extra steps for crews to guarantee the pitch trim brake is functioning correctly. A Gulfstream spokesman also told AIN that the company notified operators of 97 percent of the aircraft in the field of the problem and the manual fix before the AD was issued.

No G350/450s have experienced any pitch-trim problems stemming this issue, according to Gulfstream.