Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Distraction
Aircraft Equipment Problem Critical
Aircraft Equipment Problem Dissipated; Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action; General Declared Emergency
Aircraft
In level cruise at FL410 the first indication of a problem was monitor warning; left; failure.  Immediately after was followed by numerous CAS  messages to include; MAU 1 and 2 fail; primary pitch trim failure; loss of PIC primary flight instruments; intermittent loss of SIC flight  instruments; FMS 2 blank; FMS 1 not blank; however couldn't input any data; pressurization spikes; and CABIN ALTITUDE warning at appx  FL180. We initially asked for a lower altitude with Center; then after transferring flight controls to the right; we declared an emergency  due to the pressurization spikes and multiple system failures. Descending thru FL180 we received a CABIN ALTITUDE warning and both oxygen masked were donned until we descended below 10.000'.   At approximately 4000' as we turned on to final; both MAU [Modular Avionics Unit] malfunctions cleared and normal indications appeared on all flight instruments. The  autopilot was not engaged; and we made an uneventful landing.    During our descent; we attempted to complete the abnormal checklists; however; the multiple CAS message made that difficult to decipher  what actually was the problem.  From my experience I judged it to be a MAU failure; in this case; multiple MAU failure.  However at about the  time that I went for the checklist to address the failures; we received the red master warning CABIN ALTITUDE.  Both pilots donned the masks  and continued our descent to our cleared altitude of 9000' where they were removed.  we attempted to get the cabin to depressurize before  landing.  Descending thru approximately 4000'; the failures cleared; the approach was loaded into the FMS; and a normal landing was made.   Emergency services followed us to the ramp; and nothing abnormal was noted on the exterior of the airplane.  All throughout the event the  passengers were comfortable and we made them aware of the situation as we had time.After speaking with maintenance control; I was informed that this tail number had previously had a MAU failure.  The controller said that after  10 hours of test flights they were unable to reproduce the failure.  In order to help the crews know more about the different tail numbers that  we fly; there needs to be a process [to check maintenance history]. We should be able to enter a tail number which we are assigned and review not only  the current documents onboard and pass-down information but also recurring maintenance actions and abnormal maintenance irregularities  for the previous 60-90 days.   When the maintenance log sheets are removed from the aircraft; we are unable to see the full picture of the  airplane and troubleshoot any minor problems.
Cruise at 41;000 feet. Got a Monitor Warning Fail. Autopilot disconnected and pic started to hand fly the aircraft. We then received multiple CAS Messages and our instruments started to fail. Received big red X's on most and then would go back to normal. Captain's instruments completely failed so we transferred controls to me. Our pressurization started to intermittently spike so we informed ATC that we needed an immediate descent to 10;000 feet. We were cleared down to 9000 ft. We declared an emergency. We were trying to figure out which checklist to perform since the CAS Messages kept appearing and disappearing while pressurization kept randomly spiking. Passing through 18;000 ft we then received a RED CABIN ALTITUDE CAS Message. We then donned our oxygen masks until we leveled at 9000 ft. FMS 2 went blank and FMS 1 wouldn't accept inputs. We queried ATC about weather for possible divert possibilities. We decided on ZZZ and asked for vectors to this airport. Captain finished all necessary checklists and all CAS Messages seemed to clear at low altitudes before landing. We landing without further incident. It would be helpful to be able to pull up past maintenance write ups for each aircraft. This is also a good training scenario since the only thing to perform in a MAU FAIL CAS Checklist is leave icing conditions. It also just tells of malfunctions you will receive.
CE680 Flight Crew at FL410 experiences multiple failures possibly associated with MAU 1 and 2 failure. Pressurization is lost and flight diverts to a suitable airport. All failures cleared before landing and post flight checks revealed a history of MAU failures.