Regional Jet 700 ER/LR (CRJ700)
Flight Crew Air Transport Pilot (ATP)
Confusion
Aircraft Equipment Problem Less Severe
Weather; Manuals; Aircraft
We left the gate for a very late departure (due to an earlier divert and an aircraft swap). Approximately 20 minutes into the flight; we were climbing through FL380 when my First Officer pointed to the engine gauges and asked; 'Is that normal' The right engine fan vibe gauge was pegged at the top of the amber part of the analog gauge and the digital reading was fluctuating between 4.0 and 5.0. I turned off the ANR feature of my headset and; sure enough; the vibration noise in the cabin was significantly louder than normal. I was the pilot flying so I transferred the aircraft controls to the First Officer; asked him to take the radios; and instructed him to ask ATC for an immediate descent to FL300. I told my First Officer to slowly and smoothly reduce the thrust levers; in an effort to get the right engine fan vibe back into the green; and attempt to maintain FL300 and to fly no slower than Mach 0.71. I told him to notify me immediately if the aircraft was not able to maintain FL300 at Mach 0.71 while keeping the fan vibe in the green. While he did this; I searched the index section of the QRH for guidance on the fan vibe. I couldn't locate anything under 'Fan Vibe.' I looked under 'VIBE' and there seemed to be only N2 Vibe issues there (by all indications; the core of the engine was healthy; within limits; and operating normally). As far as I was concerned; and to my surprise; the QRH did not contain any guidance for abnormal fan vibe indications (I have since found the guidance located in the index under the term 'N1 Fan Vibe.' As it turns out; my actions roughly followed the instructions contained in the QRH anyway). So; I called Commercial Radio and spoke to Maintenance Control over the radio; informing them that I could not locate any guidance in the QRH that addressed my problem and asking them if it was safe to continue the flight. I noticed that the First Officer had been able to maintain FL300 and Mach 0.71; while keeping the fan vibe within limits at the top of the green arc. Since my engine was now operating within limits; I wanted to ensure that I was legal to continue the flight; as opposed to landing as soon as practical. Maintenance Control assured me that I was legal and safe to continue operating the flight; since all of my engine gauges were green and within limits. My next concern with continuing the flight was addressed with Dispatch. The First Officer and I discussed two primary concerns: fuel burn to our destination and alternate (which was now experiencing deteriorating weather conditions due to the line of approaching weather) and our confidence in the engine's ability to produce its full range of power in the event of a missed approach or go around. Since we had been flying at FL300; instead of our planned altitude of FL390; I discussed my new fuel burn with the Dispatcher. We agreed that I would have enough fuel to legally continue the flight. However; the bigger concern was the deteriorating weather that [our destination] was experiencing.Although the engine was currently operating within limits - in the event of a go-around due to wind shear or a missed approach would the engine be safe to operate at TOGA power or would doing so damage the engine and cause us to exceed an operating limitation? We spoke about aviation accidents and how they're always caused by not one questionable decision; but a chain of questionable decisions. We both agreed that if we decided to proceed; the choice would seem to fit the criteria of a chain of questionable decisions. With this in mind; we agreed that the safest course of action would be to divert and make a precautionary landing. We agreed to divert because the weather there was good; a spare aircraft was available to swap into and complete our flight; and Company Maintenance would be able to address the fan vibe issue and return the aircraft to service as soon as possible. We landed without incident. I believe that this incident was handled prudently and correctly. At all times; the safety of the aircraft; passengers; and crew were considered and were never compromised.
CRJ-700 flight crew noted high Fan Vibe gauge readings during climb and; after descending and slowing the aircraft; stabilized the engine within limits. After considering the aircraft problem and destination weather; crew elected to divert. Captain noted that the Fan Vibe issue was difficult to locate in the QRH.