Medium Transport; Low Wing; 2 Turbojet Eng
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance
Aircraft Aircraft Damaged; Flight Crew Landed As Precaution; General Maintenance Action
Aircraft; Human Factors; Procedure
Day 3 of a 4 day trip with same CA (Captain). We were rerouted after leg 1 to DH (Dead Head) to ZZZ and pick up and reposition to [the next airport] an airplane that had been repaired at ZZZ the night prior. When we arrived at ZZZ airplane was parked at remote parking and we had to wait nearly 2 hours for Ops personnel to get us to the aircraft. I did a thorough pre-flight external inspection of the airplane knowing it had just been returned to service and we were the first flight after that event. I did not see anything abnormal on the pre-flight inspection. We did not require a push crew from the remote parking but did have ramp personnel present to pull the chocks and marshal our engine start. Start up and taxi normal. I was pilot flying and on the initial climb after takeoff I notice that the airplane was significantly out of trim; especially in yaw. Knowing our airplane was very light and many of the airplanes are a bit crooked; I trimmed it out and continued flying the RNAV departure by hand. All flight controls felt normal. No indications present. As we accelerated the airplane began to have a definitive vibration. It was not particularly violent but definite and felt like it was coming from the forward floor area. CA agreed that we had a vibration and we began checking all EICAS indications and pages for any annunciation. None found. Above 10k I accelerated to 270 kts and the vibration became much more pronounced and concerning. After engaging the a/p I briefly commanded a climb speed of 280 kts and this made the vibration worse and the airplane did not accelerate or climb normally (it was barely doing either). Knowing that 250 kts produced the best vibration/climb characteristic; I slowed the a/c back to 250 kts. No vibration indications on either engine and all engine parameters normal. Fuel flow at 250 kts within normal range but high for an empty light airplane. I then slowly backed out the aileron and rudder trims towards neutral to see if that may help the vibration or change what we were seeing. It did not so I reset the trims to square the airplane. At this point climb characteristics were noticeably poor even at 250 knots (approx 17k MSL) so we agreed that requesting to level off at a lower altitude and ask ATC to provide us with 250 kts was the best course of action while we considered our situation. The vibrations were not bad or getting worse and the airplane handled fine at this airspeed/alt combination so we decided we had time to investigate. We looked through the maintenance logs for any vibration history (some a/c have them); talked through various scenarios with the nose door and asked dispatch for any additional maintenance history they could provide over ACARS. One possibility we considered was that perhaps the diversion from the warning message the previous day (land nearest suitable airport QRH for 14th stage warning) resulted in a hard landing that had caused something wrong in the nose gear bay. We briefed how this could cause landing gear problems on approach. We did not declare an emergency but did inform dispatch of our speed/altitude requests. We decided on initial approach there was no reason to request the longer runway unless we had difficulty configuring the airplane on approach. I configured the airplane early coming in to [the destination airport] to make sure that all was set with plenty of time prior to landing. I noticed that at low power setting the large trim needs (especially yaw) decreased. Landing and taxi normal. On my post-flight walk-around I noticed the RH aft upper engine cowl was unlatched and hinged upward. Maintenance was called. Outstation maintenance supervisor and compliance to ensure that cowls/doors/access points are properly attached and secured. While the cowling appeared secure during the walk-around; perhaps a more thorough pre-flight check after a maintenance event could have caught this problem. More information in the corrective action of theaircraft log to inform the crew what pieces of the airplane maintenance actually had to take apart to alert the crew to make double sure to dig deeper into those places on preflight after return to service. Some training on performance loss associated with the missing cowl piece -- it made perfect sense to us after we saw it on preflight but it wasn't where our minds were going when we troubleshot the vibration in-flight.
CRJ-200 First Officer reported vibrations due to an unlatched upper engine cowling.