An Air Carrier aircraft departed SMF and developed a vibration during the post takeoff clean up. The crew did not determine the cause until after landing at their destination where three fan blades were found damaged; presumably by a bird.
Synopsis
An Air Carrier aircraft departed SMF and developed a vibration during the post takeoff clean up. The crew did not determine the cause until after landing at their destination where three fan blades were found damaged; presumably by a bird.
Narrative
The engine start; taxi; and takeoff were normal. As we finished cleaning up the aircraft; we heard a vibration noise. We checked the pressurization and engine instruments and everything was normal. As we climbed; the noise held steady initially. The flight attendants called to say they heard it and it seemed loudest in the aft galley. At this point; we were thinking a door seal was making the noise and we confirmed normal pressurization. We also considered that the engines were out of sync; and modulating the engines did change the tone of the noise; but didn't stop it. We checked the QRH; but found nothing that applied to our situation. At this point we discussed turning back but; given all the normal indications; we elected to continue and monitor. As the climb progressed the noise decreased appreciably. The flight attendants confirmed it was much better in the back. We leveled off and everything seemed to be OK. Later on though; the flight attendants called and said the noise had started again and they felt a vibration as well. At this point; we felt that the aircraft obviously had an issue that needed to be looked at. As all indications were still normal and we were approaching our descent; we elected to continue on to our planned destination. As we pulled the power back in the descent; the noise improved and stayed fairly quiet until we powered back up in the destination traffic pattern. By then we were pretty sure there was an engine issue even though all indications continued to be normal. Sure enough; after landing; we found damage to three fan blades in the number two engine. The only thing that made sense to us was that we'd hit a bird at some point after takeoff. I really wish we'd turned back when we noticed the noise; but the normal indications and the fact that the noise decreased significantly during the climb and level off led us to make a bad decision. I was also lulled into a false sense of security because I've had noise issues in the past that resolved during the climb; which is what I thought happened here. Evaluate the situation on its own (not on what's happened in the past) and be conservative. When we discussed turning back; we should have. Our crew communication was good; I thought; but we still made the wrong decision.
Second reporter narrative
I was the pilot flying on a flight. The preflight and takeoff were uneventful. Shortly after takeoff; during the clean-up and initial climb; we noticed an unusual vibration/rumbling noise. My initial thought was there was a pressurization or configuration problem but we could not find any indication of either. We both carefully analyzed the engine indications and found them matched and normal. I noticed the noise changed tone when modulating power; particularly on the number two engine. We ran the High Engine Vibration Checklist but the QRH did not direct any action with vibration meter below 4; ours read steady at 1.5. The Flight Attendant called forward to report a louder than usual noise in the cabin; particularly aft; and the aft galley floor had a perceptible vibration. As we continued to climb and try to figure out the problem; the noise seemed to lesson as confirmed by the flight attendants. It was nearly normal sounding when the power was reduced for cruise. The Captain and I discussed returning to the originating airport; however; at this point the normal indications; the QRH guidance; and the lessening noise (confirmed by the cabin crew) led to the decision to continue. Only after seeing the damage did I understand the potential seriousness of our situation. In hindsight; I should have listened to my instincts and returned to the originating airport; despite all of the objective analysis. We are paid to exercise our judgment based on our experience; skill; and instinct. In this case I let the book and thoughts of customer inconvenience get in the way of that. It was a learning experience for me and given the same scenario; I would definitely choose a different course of action.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.