Narrative:

This incident started on the ground during our takeoff roll at our departure airport. Upon advancing the thrust levers for takeoff; the left engine N1 indication was unstable; and consequentially unreadable. Captain asked me (first officer) to set thrust as per standard profile. I was able to set the right engine thrust and estimate the left engine position based on where the right engines lever was.continued takeoff without incident and the N1 gauge eventually stabilized later in the takeoff roll and continued to stabilize on the initial climb. Continued with the flight as normal. Later in the climb; at roughly 15;000 feet; we noticed the N1 become erratic and unstable once again. Initially; interstage turbine temperature (itt) and N2 remained stable indicating a sensor issue. However; as the issue progressed; itt and N2 on engine 1 also demonstrated abnormal indications. Crew discussed what to do and determined we would monitor; as the engine was still running normally. The only abnormal indications were the gauges.captain did manipulate the thrust lever to attempt and diagnose what was happening. Engine would stabilize at lower power settings; but would become quite erratic at climb or standard cruise power settings. Reaching roughly 19;000 feet; the engine started to surge up and down to the point of being obviously noticeable to the flight crew; and possibly dangerous. At this point we recognized that there may be a bigger threat than what was initially discussed. Crew calculated the drift down altitude with a single engine to be 21;000 feet at the current weight and requested to level off at that altitude with ATC. We were then assigned FL210.during the level off; the surging of the number 1 engine persisted and the erratic engine indications became worse. Crew felt uncomfortable with that engine and the decision was made to divert to the nearest suitable airport 35 miles off of our nose. Captain and first officer discussed if we should [request priority handling] and the captain said no. Control of the aircraft was given to the first officer to initiate a descent and setup for the ILS into ZZZ. Weather was obtained in the process. Captain advised the flight attendants and passengers of the situation as we descended with thrust levers idle.the need for anti-ice was met descending through 12;000 feet where both engines were advanced to gain adequate pressure. Erratic indications persisted eventually showing N1 at 0%. Itt had also shown an over temperature during the descent with medium thrust. Captain turned on the continuous ignition as a precaution as the crew re-established communication from where we had left off to split up duties. Crew had both mentioned completing a QRH procedure; but could not think of a specific procedure to accomplish and also did not want to perform a procedure that would secure the engine; so we continued with our normal checklists for landing. On final; engine 1 N1 continued to show 0% while it appeared that we were getting thrust from that engine. At that point; the crew decided to [request priority handling] as an additional precaution.a landing was made without any issues and we taxied to the gate. Dispatch was notified during flight of the diversion. Once on the ground; an inspection of both engines noted no obvious damage of any kind. After the incident; first officer found an abnormal QRH procedure that would have fit the symptoms that the engine was giving us. During numerous run ups with mechanics onboard; it was discovered that none of the QRH procedures would have resolved any of the issues presented. Numerous run ups were accomplished with mechanics onboard and maintenance control on the phone with no issues resolved.mechanics swapped out the computers that control the N1 fan to see if it was a sensor issue and it was determined that it was not. The crew determined this event to be a no time threat in flight; forcing us to make a decision quickly to avoid any further issues. The result of that decision was an immediate diversion whereas we would be on the ground within minutes and could deal with the issue then. There was a suitable airport less than 40 miles away. It took us between 5-10 minutes from deciding to divert to landing safely. If we had continued to fly while trying to find a QRH procedure that we were unsure even existed; it would have been a poor decision and could have resulted in a negative outcome. Crew determined that this was the best course of action given the information we had.event was caused by some sort of mechanical anomaly that is still unknown. Mechanics on the ground were able to replicate the issue and unable to resolve or diagnose what the issue was.I strongly believe that we made the best possible decision given the information we were dealt. In the future; completing a QRH checklist may have changed the outcome; possibly avoiding a diversion. This was not an event that any QRH procedure would have assisted. It would have hindered either by taking up time that we used to get on the ground quickly; or by having us shut down an engine and force us to land single engine. Either way; the threat would have been higher if we did not land as soon as practical as we did in this circumstance.

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Original NASA ASRS Text

Title: CRJ-200 crew reported left engine N1 indication was initially unstable on takeoff; settled down and then engine started surging at altitude. Crew elected to divert.

Narrative: This incident started on the ground during our takeoff roll at our departure airport. Upon advancing the thrust levers for takeoff; the left engine N1 indication was unstable; and consequentially unreadable. Captain asked me (First Officer) to set thrust as per standard profile. I was able to set the right engine thrust and estimate the left engine position based on where the right engines lever was.Continued takeoff without incident and the N1 gauge eventually stabilized later in the takeoff roll and continued to stabilize on the initial climb. Continued with the flight as normal. Later in the climb; at roughly 15;000 feet; we noticed the N1 become erratic and unstable once again. Initially; Interstage Turbine Temperature (ITT) and N2 remained stable indicating a sensor issue. However; as the issue progressed; ITT and N2 on engine 1 also demonstrated abnormal indications. Crew discussed what to do and determined we would monitor; as the engine was still running normally. The only abnormal indications were the gauges.Captain did manipulate the thrust lever to attempt and diagnose what was happening. Engine would stabilize at lower power settings; but would become quite erratic at climb or standard cruise power settings. Reaching roughly 19;000 feet; the engine started to surge up and down to the point of being obviously noticeable to the flight crew; and possibly dangerous. At this point we recognized that there may be a bigger threat than what was initially discussed. Crew calculated the drift down altitude with a single engine to be 21;000 feet at the current weight and requested to level off at that altitude with ATC. We were then assigned FL210.During the level off; the surging of the number 1 engine persisted and the erratic engine indications became worse. Crew felt uncomfortable with that engine and the decision was made to divert to the nearest suitable airport 35 miles off of our nose. Captain and First Officer discussed if we should [request priority handling] and the Captain said no. Control of the aircraft was given to the First Officer to initiate a descent and setup for the ILS into ZZZ. Weather was obtained in the process. Captain advised the flight attendants and passengers of the situation as we descended with thrust levers idle.The need for anti-ice was met descending through 12;000 feet where both engines were advanced to gain adequate pressure. Erratic indications persisted eventually showing N1 at 0%. ITT had also shown an over temperature during the descent with medium thrust. Captain turned on the continuous ignition as a precaution as the crew re-established communication from where we had left off to split up duties. Crew had both mentioned completing a QRH procedure; but could not think of a specific procedure to accomplish and also did not want to perform a procedure that would secure the engine; so we continued with our normal checklists for landing. On final; engine 1 N1 continued to show 0% while it appeared that we were getting thrust from that engine. At that point; the crew decided to [request priority handling] as an additional precaution.A landing was made without any issues and we taxied to the gate. Dispatch was notified during flight of the diversion. Once on the ground; an inspection of both engines noted no obvious damage of any kind. After the incident; First Officer found an abnormal QRH procedure that would have fit the symptoms that the engine was giving us. During numerous run ups with mechanics onboard; it was discovered that none of the QRH procedures would have resolved any of the issues presented. Numerous run ups were accomplished with mechanics onboard and Maintenance Control on the phone with no issues resolved.Mechanics swapped out the computers that control the N1 fan to see if it was a sensor issue and it was determined that it was not. The crew determined this event to be a no time threat in flight; forcing us to make a decision quickly to avoid any further issues. The result of that decision was an immediate diversion whereas we would be on the ground within minutes and could deal with the issue then. There was a suitable airport less than 40 miles away. It took us between 5-10 minutes from deciding to divert to landing safely. If we had continued to fly while trying to find a QRH procedure that we were unsure even existed; it would have been a poor decision and could have resulted in a negative outcome. Crew determined that this was the best course of action given the information we had.Event was caused by some sort of mechanical anomaly that is still unknown. Mechanics on the ground were able to replicate the issue and unable to resolve or diagnose what the issue was.I strongly believe that we made the best possible decision given the information we were dealt. In the future; completing a QRH checklist may have changed the outcome; possibly avoiding a diversion. This was not an event that any QRH procedure would have assisted. It would have hindered either by taking up time that we used to get on the ground quickly; or by having us shut down an engine and force us to land single engine. Either way; the threat would have been higher if we did not land as soon as practical as we did in this circumstance.

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.