Citation X (C750)
Maintenance Powerplant; Maintenance Airframe
Training / Qualification; Troubleshooting; Situational Awareness; Communication Breakdown; Confusion; Human-Machine Interface
Aircraft Equipment Problem Critical
General Maintenance Action
Procedure; Manuals; Human Factors; Aircraft
A Cessna Citation X (C750); Aircraft X; had a long history of the following message: FADEC FAIL/FAULT L A/B [Left Fadec Channel A/B Fault]. This fault had first showed up after a Phase Inspection in ZZZ1 in January 2012 and wasn't repaired until May 2012.  The message would first appear during landing after the thrust reversers were deployed. They would always deploy with no defects. During the five months the FADEC Fail /Fault message would appear which never resulted in an engine shutdown.   One of the main reasons Maintenance was not able to duplicate the fault or repair it in a timely manner was the lack of required fault codes needed to find the cause of the issue at hand.  The fault codes are only present while the Crew Alerting System (CAS) message is displayed.    There were a number of factors that made it difficult for the Maintenance Controllers to find the appropriate codes; including: new Controllers; Crewmembers that were unfamiliar with retrieving the codes from the Intergrated Maintenance Computer (IMC) computer; (US) Customs (telling Crewmember to shut down the aircraft) and message not staying 'latched'.  Approximately fifteen Maintenance events happened during this time frame; as well as a number of taxi checks; test flights; and maintenance engine run-ups with thrust reversers being deployed.    I first became aware of this problem as a Maintenance Controller in March 2012; when the aircraft broke in ZZZ2.  During the following weeks I made it a point to track this aircraft.  It was frustrating to hear about missed opportunities of getting the fault codes.   After I started tracking this particular aircraft's progress; eight maintenance events followed.  Out of those eight events; only three engine codes events were recovered; I was involved in two events. It was my familiarity with the IMT which led us to look at other areas. We found that it was a wire harness issue which had been causing the problem.  In May 2012; I received a call from the Captain on Aircraft X; telling me he had a FADEC Fail L-AB. I asked him if the engine had shutdown. He said; 'No'.  Then I replied to him that the message you had must be a fault and he replied; 'No'; it was a fail L-AB. He told me he had to shut down the aircraft. I told him Maintenance would not be able to find anything wrong with the aircraft because the message disappeared.  He still felt that Maintenance needed to inspect the aircraft. They found nothing wrong with the aircraft; and the next day he flew the aircraft to Cessna Service Center.  The aircraft was inspected; then taxi checked and flight tested twice with no faults found.  Recommend flight crewmembers become familiar with retrieving the fault codes from the IMT computer.
Reporter stated the FADEC FAIL/FAULT L A/B fault messages only occurred during landing; when the Allison AE 3007C1 engine thrust reversers deployed on the Citation X (C750) aircraft. There is an inherent design problem with the engine FADEC System because FADEC does not 'latch'; or 'hold'; fault messages unless some sort of electrical power is on the aircraft. Without aircraft electrical power; all FADEC fault codes are lost.Reporter stated that is different from the Fault Warning Computer (FWC) and other systems on the Citation X that do latch fault codes even after electrical power has been removed.  The Digital Acquisition Unit (DAU) grabs all information; including FADEC; then sends signals to the Fault Warning Computer (FWC) which sends signals to the EFIS System.Reporter stated that because of the FADEC design flaw; the importance of flight crews to become familiar with retrieving FADEC fault codes prior to shutting down aircraft power becomes very important when troubleshooting causes of FADEC FAIL/FAULT messages. Two wire harnesses involved with the left engine Pressure and Air Data Computer that caused the chronic FADEC fault messages were replaced.  The aircraft manufacturer does not appear interested in addressing his concerns about the inability of the FADEC System to latch faults after aircraft electrical power is removed.
A Maintenance Controller reports about a design flaw in the Engine FADEC System on Cessna Citation X (C750) aircraft that does not allow 'latching'of FADEC fault messages when aircraft electrical power is removed. Lack of flight crew familiarity retrieving FADEC fault codes prior to removing electrical power limits Maintenance trouble shooting.