Date: 201509
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Weather elements / visibility: Turbulence; Thunderstorm
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: Yesterday we experienced a maintenance problem that required us to land at the nearest suitable airport.  The plane we were flying had a MEL that required the #2 generator be deferred.  As a result the APU had to be run continuously throughout the flight to provide electrical power.  The MEL procedure was followed and takeoff; climb; and cruise went normal like any other flight.  However during cruise we got an APU oil press caution message.  I had the controls but I transferred them and the radios to my FO (First Officer) so I could run the QRH procedure.  It was followed; and the end of the checklist directed us to land at nearest suitable airport since the APU generator was essential for flight and it couldn't be shut down.  Before the QRH was completed Approach started us on our descent into [destination].  I was in communication with dispatch about a possible diversion and potential airports that would work.  We were around 20 minutes from [destination] and already set up for the arrival and landing into there with current weather.  After starting our descent the APU oil temp caution message also appeared.  After running the QRH we still had the same agenda to continue on to [destination] and land as soon as possible.  Although we could have been to [several alternate airports] faster we could see the buildups and severe line of thunderstorms out the window and also on radar moving along the east coast.  Before each flight it's a habit of mine to check our filed flight plan route to check for any possible weather we may encounter; and I saw the mentioned thunderstorms and made a mental note.  As a result of the weather and potential suitable airports we decided to continue on instead of diverting.  After landing without incident (no emergency was declared) maintenance was called in and it was discovered that the APU oil cap had been left off by the mechanics doing an inspection on the APU.  The APU was damaged and the return flight had to be cancelled so more maintenance could be performed later that night and new parts installed.  I feel confident in my choice to continue and the dispatcher later agreed with me that the choice we made was the safest and best one possible.


Second narrative: [Report narrative contained no additional information.]


Synopsis: CRJ-200 flight crew reported they lost the APU which was their second generator. Failure was later traced to APU oil cap missing.