Date: 201512
Weather elements / visibility: Rain
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Aircraft component: Indicating and Warning - Fuel System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Situational Awareness; Workload; Time Pressure
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate
Result: Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: I'm still perplexed as to why the fuel predictive modeler showed a rapid drop in available fuel once established in cruise and LRC power settings; followed by a rapid increase of over 1000 LBS on approach to landing. This should not have happened in the fuel predictive model. Running the fuel calculations manually we expected to have more; but we decided to err on the side of caution.Still being relatively new and never having had to divert before; and dealing with constant messages from dispatch; I was getting a little task saturated in my duties on this leg and this continued once we got on the ground with the termination of the flight and the disembarking of grumpy passengers. With the change of crew and termination of the flight we failed to contact maintenance regarding the fuel predictive modeler showing 1600 LBS which is what lead to the [advising ATC of fuel situation] and then rapidly increasing to 2600 LBS on approach.This happened on the last leg of our first day; of the four day trip. At the time of our departure we were +1000 LBS over our minimum fuel requirement for the flight. Operationally we were already several hours delayed and in an extended FDP period. Due to weather and congestion; upon arriving into the destination area we were slowed aprox 250 miles out to 250 KIAS and then told to backtrack on a 180 degree reversal in lieu of holding. We queried ATC about our position and found that we were number 12 in line. At this point we checked our fuel and found that we were at our bugout fuel limit and had to proceed on to our alternate. We headed towards our alternate and set LRC power. About 1/2 way to our alternate our fuel predictive modeler rapidly decreased to 1600 LBS of fuel estimated at arrival to our alternate. We could not account for the drop and decided to err on the side of caution and [advise ATC] to receive priority handling. We stayed high and executed an idle descent to a visual approach and landing. On the approach to landing; the fuel predictive modeler rapidly increased available fuel and after landing the totalizer showed 2600 lbs. At time of shutdown we had 2580 LBS remaining.After my walk around and the captain's announcement to the passengers; we should have contacted maintenance and followed on from there before we departed the aircraft.




Synopsis: A CRJ900 pilot neglected to write up a fuel indicating problem after diverting. The fuel totalizer showed a rapid drop in available fuel in cruise.