Narrative:

Approximately 250 miles west of ZZZ; the number 1 engine N1 vibration indicator started flashing; it was above 5.0. The captain was in the restroom at this time. When he got back to the cockpit just a few minutes later the vibration indicator was above 8.0; it got up to a high of about 8.5. This was also accompanied by a noticeable airframe rumble or vibration; similar in nature to the vibration or rumble we hear in the airbus when the landing lights are extended at the higher air speeds; like just before retracting the landing light passing 10;000 ft. I took the aircraft and radios and the captain handled the checklist and radio/ACARS communication with maintenance control and dispatch; etc. I heard some but not all of that interchange since I was flying and talking with ATC. Other than the vibration indications; all other engine indications were normal throughout the flight. As per the checklist; the throttle in question was pulled back to a setting where the vibration indication dropped below 5.0. On the initial reduction the vibration indication was reduced to about 1.5 or so and the airframe vibration/rumble stopped completely. We descended to about 26;000 ft; maintaining altitude and airspeed was not a problem; and the engine seemed to be operating normally. All indications were normal. While all this was in progress; I checked weather for several possible alternates. I also notified ATC of our possible intent to divert. By the time we finished reviewing the checklist and by the time the captain had terminated discussions with the aforementioned agencies; we were now much closer to ZZZ and actually in a position to make a near normal profile descent into the ZZZ airport. At this time at the lower altitude the engine was operating fine; within vibration limits; even at higher thrust settings. As a precaution we kept the engine at a lower thrust setting. Also; at this point in time the diverting to one of the possible alternates would have necessitated a course reversal. ZZZ seemed like the most reasonable and closest alternate at this point in time. It also had one of the longer runways. I think this was a comforting thought for us; especially after a very long duty day; over 13 hours I think; and a 2am landing. On the previous leg we had experienced a flap malfunction and we landed in ZZZ1 at high speed with no flaps; slats only. We used quite a bit of runway in that scenario. One note to add here. On the walk around in ZZZ1 I noticed a fluid leak from the number 1 engine drain mast. We wrote it up and notified maintenance. Maintenance decided to do an engine run up. The passengers were deplaned. Then maintenance changed its mind and decided a run up was not required. The passengers were re boarded. They told us that they had found the problem. It was; I think; one of those 'acceptable parameter' leaks; possibly around the engine oil cooler; but I am not sure about that; I can't remember exactly. Anyway; the item was signed off. I expressed my doubts to the captain about the efficacy of this fix since no corrective action was actually taken. I do know that some leakage is acceptable in certain cases. When we experienced the vibration problem in flight I also told the captain that the drain mast leak and the vibration problem were probably related. I have to state here that this is pure conjecture on my part; with no actual proof; but it was my gut feeling as a pilot. I would like to relate what happened on a previous trip a few weeks prior because it may shed some light or have some bearing on the event now in question. Just a couple of weeks prior; I found a similar drain mast leak. They had only one mechanic there and they wanted us (the pilots) to do an engine run up. We refused to do the run up. The flight cancelled and we stayed over night. The next morning two mechanics were flown in and they found the problem. It was an internal engine O ring; in a critical part of the hot section that was 'fried and hardlike plastic'; their words not mine. A part was flown in later that morning and the engine repaired. I asked the mechanics if this problem might have caused an in flight engine failure/loss of oil/possible engine shutdown due to fluid loss; etc. The answer was yes. I also asked them if; doing a run up; the leak would have dissipated; or 'gone away'; at least to the naked eye; because a static leak could be blown out the back of a running engine. The answer again was yes. I believe we may have likely averted an in flight problem with this engine by refusing the run up and by essentially mandating that the proper number of qualified mechanics properly address the problem.

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Original NASA ASRS Text

Title: A320 First Officer experiences high N1 vibration (5 units) at FL350; which increases to 8 units in the next few minutes. As thrust is reduced for descent and landing at destination the vibration is reduced to 1.5 units and does not return.

Narrative: Approximately 250 miles west of ZZZ; the number 1 engine N1 vibration indicator started flashing; it was above 5.0. The Captain was in the restroom at this time. When he got back to the cockpit just a few minutes later the vibration indicator was above 8.0; it got up to a high of about 8.5. This was also accompanied by a noticeable airframe rumble or vibration; similar in nature to the vibration or rumble we hear in the Airbus when the landing lights are extended at the higher air speeds; like just before retracting the landing light passing 10;000 FT. I took the aircraft and radios and the Captain handled the checklist and radio/ACARS communication with Maintenance Control and Dispatch; etc. I heard some but not all of that interchange since I was flying and talking with ATC. Other than the vibration indications; all other engine indications were normal throughout the flight. As per the checklist; the throttle in question was pulled back to a setting where the vibration indication dropped below 5.0. On the initial reduction the vibration indication was reduced to about 1.5 or so and the airframe vibration/rumble stopped completely. We descended to about 26;000 FT; maintaining altitude and airspeed was not a problem; and the engine seemed to be operating normally. All indications were normal. While all this was in progress; I checked weather for several possible alternates. I also notified ATC of our possible intent to divert. By the time we finished reviewing the checklist and by the time the Captain had terminated discussions with the aforementioned agencies; we were now much closer to ZZZ and actually in a position to make a near normal profile descent into the ZZZ airport. At this time at the lower altitude the engine was operating fine; within vibration limits; even at higher thrust settings. As a precaution we kept the engine at a lower thrust setting. Also; at this point in time the diverting to one of the possible alternates would have necessitated a course reversal. ZZZ seemed like the most reasonable and closest alternate at this point in time. It also had one of the longer runways. I think this was a comforting thought for us; especially after a very long duty day; over 13 hours I think; and a 2am landing. On the previous leg we had experienced a flap malfunction and we landed in ZZZ1 at high speed with no flaps; slats only. We used quite a bit of runway in that scenario. One note to add here. On the walk around in ZZZ1 I noticed a fluid leak from the number 1 engine drain mast. We wrote it up and notified Maintenance. Maintenance decided to do an engine run up. The passengers were deplaned. Then Maintenance changed its mind and decided a run up was not required. The passengers were re boarded. They told us that they had found the problem. It was; I think; one of those 'acceptable parameter' leaks; possibly around the engine oil cooler; but I am not sure about that; I can't remember exactly. Anyway; the item was signed off. I expressed my doubts to the Captain about the efficacy of this fix since no corrective action was actually taken. I do know that some leakage is acceptable in certain cases. When we experienced the vibration problem in flight I also told the Captain that the drain mast leak and the vibration problem were probably related. I have to state here that this is pure conjecture on my part; with no actual proof; but it was my gut feeling as a pilot. I would like to relate what happened on a previous trip a few weeks prior because it may shed some light or have some bearing on the event now in question. Just a couple of weeks prior; I found a similar drain mast leak. They had only one mechanic there and they wanted us (the pilots) to do an engine run up. We refused to do the run up. The flight cancelled and we stayed over night. The next morning two mechanics were flown in and they found the problem. It was an internal engine O ring; in a critical part of the hot section that was 'fried and hardlike plastic'; their words not mine. A part was flown in later that morning and the engine repaired. I asked the mechanics if this problem might have caused an in flight engine failure/loss of oil/possible engine shutdown due to fluid loss; etc. The answer was yes. I also asked them if; doing a run up; the leak would have dissipated; or 'gone away'; at least to the naked eye; because a static leak could be blown out the back of a running engine. The answer again was yes. I believe we may have likely averted an in flight problem with this engine by refusing the run up and by essentially mandating that the proper number of qualified mechanics properly address the problem.

Data retrieved from NASA's ASRS site as of July 2013 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.