Narrative:

[We] picked up aircraft from maintenance facility. Initial climb out was uneventful; but ATC was slow clearing us to our assigned altitudes; with frequent level offs. We had leveled at FL240; and the aircraft had accelerated to about 320 KIAS when we were given a climb to FL380; roughly 30 minutes into the flight. I started the climb with a slow deceleration (aircraft was light) toward the profile climb speed. As the aircraft went through FL250 I thought I detected a noise and vibration. ATC had asked for an expedited climb; so we were climbing at roughly 2;200 FPM. By the time we past FL260; the vibration/noise was quite pronounced and clearly getting worse; we discussed it briefly; and I had my partner ask for a level off. ATC promptly granted FL280. By this time; the airspeed had slowed to around 290 KIAS; and the vibration was continuous. I opted to continue to slow down; anticipating a possible need for a descent while we discussed the situation. The vibration could be felt in the floorboards; and heard throughout the cabin. It had a distinctly airframe feeling to it. We reduced power in an attempt to see if this was some sort of harmonic issue; but throttle position made no difference. However; as we slowed toward 260 KIAS the vibration/noise slackened significantly; becoming quite small at 260 with a cyclic quality. As we leveled; and attempted to return to a normal cruse airspeed; the vibration began to build again as we accelerated past 270; so we immediately abandoned any further experiments and kept the airplane below 270. My thoughts ran to an open service or gear door; however we had no indications; and we had both carefully checked the service doors in accordance with the preflight checklist and fom before engine start. Systems all appeared normal; and as the vibration did not seem to pose any immediate threat (once we had slowed down) the question became where do we land? I called the company and described the situation; giving our position. The company suggested a preferred airport; and coordinated a re-release while we coordinated with ATC (via my partner). In retrospect; this was likely a poor decision on our part; we should have gone to a closer suitable airport which was just to our north; however the vibration had abated to the point where we thought it did not pose an immediate threat to the aircraft. When we made that decision; we both thought we were much closer to the company recommended airport than we really were; time wise; as ATC had given us an initial estimate of 20 minutes; which would have been perfect for the time/distance we needed to descend and configure the airplane early in case of problems. We should have asked the FMS before making the decision. It turned out to be nearly 40 minutes farther on at our reduced speed; but we had already committed with both ATC and the company and decided to continue with the plan. Regardless; the time proved helpful. We discussed various possible scenarios; including a gear malfunction or unanticipated flight control problem; and laid out a plan to keep the aircraft slow; and configure it for landing early and high in case a more serious problem came up. In the descent; we noted a rumbling several times during the descent; but nothing like we had experienced earlier; although we did keep the speed below 270. We opted to lower the gear early (15 miles out) and slowed the aircraft to 165 KIAS before doing so to reduce any air loads on the gear doors; in case that was the source of the problem. The gear cycled normally; however; the slipstream noise in the cockpit was abnormally high. It was so loud that we would have had to shout if not for the intercom and headsets. This is completely abnormal for a falcon at that airspeed. The noise diminished as we slowed toward landing; but was still at an elevated level from the normal range. After a normal landing; we verified all the doors were closed and locked; and there was nothing obviously wrong with the aircraftthat the eye could detect. I have no idea what is wrong with the aircraft. There are several possibilities; such as issues with the nose cone venting system (my bet is there); or possibly some sort of issue with the ecu's jet pump valve which begins to close as the aircraft approaches 300 KIAS. As for our handling of the situation; since there was no immediate threat; we shouldn't have jumped at the first suggestion given us; however we both expected airports near where the company suggested; and so it fit our predisposition; even though we did not have accurate data about the distance to those airports. Otherwise; I felt we handled the situation quite well.

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Original NASA ASRS Text

Title: A DA-2000 Captain reported an unusual and strong airframe vibration on a post maintenance flight which resulted in deviating to a Company recommended airport which was not the nearest suitable for landing.

Narrative: [We] picked up aircraft from maintenance facility. Initial climb out was uneventful; but ATC was slow clearing us to our assigned altitudes; with frequent level offs. We had leveled at FL240; and the aircraft had accelerated to about 320 KIAS when we were given a climb to FL380; roughly 30 minutes into the flight. I started the climb with a slow deceleration (aircraft was light) toward the profile climb speed. As the aircraft went through FL250 I thought I detected a noise and vibration. ATC had asked for an expedited climb; so we were climbing at roughly 2;200 FPM. By the time we past FL260; the vibration/noise was quite pronounced and clearly getting worse; we discussed it briefly; and I had my partner ask for a level off. ATC promptly granted FL280. By this time; the airspeed had slowed to around 290 KIAS; and the vibration was continuous. I opted to continue to slow down; anticipating a possible need for a descent while we discussed the situation. The vibration could be felt in the floorboards; and heard throughout the cabin. It had a distinctly airframe feeling to it. We reduced power in an attempt to see if this was some sort of harmonic issue; but throttle position made no difference. However; as we slowed toward 260 KIAS the vibration/noise slackened significantly; becoming quite small at 260 with a cyclic quality. As we leveled; and attempted to return to a normal cruse airspeed; the vibration began to build again as we accelerated past 270; so we immediately abandoned any further experiments and kept the airplane below 270. My thoughts ran to an open service or gear door; however we had no indications; and we had both carefully checked the service doors in accordance with the preflight checklist and FOM before engine start. Systems all appeared normal; and as the vibration did not seem to pose any immediate threat (once we had slowed down) the question became where do we land? I called the company and described the situation; giving our position. The company suggested a preferred airport; and coordinated a re-release while we coordinated with ATC (via my partner). In retrospect; this was likely a poor decision on our part; we should have gone to a closer suitable airport which was just to our north; however the vibration had abated to the point where we thought it did not pose an immediate threat to the aircraft. When we made that decision; we both thought we were much closer to the Company recommended airport than we really were; time wise; as ATC had given us an initial estimate of 20 minutes; which would have been perfect for the time/distance we needed to descend and configure the airplane early in case of problems. We should have asked the FMS before making the decision. It turned out to be nearly 40 minutes farther on at our reduced speed; but we had already committed with both ATC and the Company and decided to continue with the plan. Regardless; the time proved helpful. We discussed various possible scenarios; including a gear malfunction or unanticipated flight control problem; and laid out a plan to keep the aircraft slow; and configure it for landing early and high in case a more serious problem came up. In the descent; we noted a rumbling several times during the descent; but nothing like we had experienced earlier; although we did keep the speed below 270. We opted to lower the gear early (15 miles out) and slowed the aircraft to 165 KIAS before doing so to reduce any air loads on the gear doors; in case that was the source of the problem. The gear cycled normally; however; the slipstream noise in the cockpit was abnormally high. It was so loud that we would have had to shout if not for the intercom and headsets. This is completely abnormal for a Falcon at that airspeed. The noise diminished as we slowed toward landing; but was still at an elevated level from the normal range. After a normal landing; we verified all the doors were closed and locked; and there was nothing obviously wrong with the aircraftthat the eye could detect. I have no idea what is wrong with the aircraft. There are several possibilities; such as issues with the nose cone venting system (my bet is there); or possibly some sort of issue with the ECU's jet pump valve which begins to close as the aircraft approaches 300 KIAS. As for our handling of the situation; since there was no immediate threat; we shouldn't have jumped at the first suggestion given us; however we both expected airports near where the Company suggested; and so it fit our predisposition; even though we did not have accurate data about the distance to those airports. Otherwise; I felt we handled the situation quite well.

Data retrieved from NASA's ASRS site as of April 2012 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.