Narrative:

In cruise flight at FL390; and with 40 minutes remaining in the flight; we heard the engines come out of sync. Referencing the instruments; we noticed the right hand engine N1 fluctuating roughly 1% as well as the N2 and fuel flow. It would settle down after about 30 seconds. We had mach hold on at the time. We elected to turn off mach hold and continue to monitor. The right hand engine proceeded to do this 1% fluctuation 2 more times. Time frame between these events was maybe 3-5 minutes. We began talking about diverting to ZZZ1 if it continued to get worse. At the moment ATC called us to slow us down for flow into ZZZ; the right hand N1 went from 85% to 70% with an associated yaw to the right. We told ATC we were having an engine issue and requested a lower altitude in the event the right engine failed completely. ATC gave us FL310. We requested direct ZZZ1. ATC then cleared us to 12;000. Captain spoke to the passengers and company. I maintained PF duties while captain coordinated and monitored throughout the descent and uneventful landing. During the descent; the engine never had another fluctuation but we did get the right fadec fail cas message. We completed the checklist. After shutdown on the ramp; we had a right engine minor fault and download fadec messages. In the current faults page; it indicted a hmu failure associated with the fuel system of the right engine. Captain entered each of these as grounding write ups in the logbook in coordination with maintenance.

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Original NASA ASRS Text

Title: Challenger 350 Captain reported losing N1 in the number 2 engine; resulting in a HMU [Hydro Mechanical Unit] failure in the engine.

Narrative: In cruise flight at FL390; and with 40 minutes remaining in the flight; we heard the engines come out of sync. Referencing the instruments; we noticed the right hand engine N1 fluctuating roughly 1% as well as the N2 and fuel flow. It would settle down after about 30 seconds. We had MACH HOLD on at the time. We elected to turn off MACH HOLD and continue to monitor. The right hand engine proceeded to do this 1% fluctuation 2 more times. Time frame between these events was maybe 3-5 minutes. We began talking about diverting to ZZZ1 if it continued to get worse. At the moment ATC called us to slow us down for flow into ZZZ; the right hand N1 went from 85% to 70% with an associated yaw to the right. We told ATC we were having an engine issue and requested a lower altitude in the event the right engine failed completely. ATC gave us FL310. We requested direct ZZZ1. ATC then cleared us to 12;000. Captain spoke to the passengers and company. I maintained PF duties while Captain coordinated and monitored throughout the descent and uneventful landing. During the descent; the engine never had another fluctuation but we did get the R FADEC FAIL cas message. We completed the checklist. After shutdown on the ramp; we had a R ENGINE MINOR FAULT and DOWNLOAD FADEC messages. In the current faults page; it indicted a HMU failure associated with the fuel system of the right engine. Captain entered each of these as grounding write ups in the logbook in coordination with maintenance.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.