Date: 201503
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Aircraft component: APU Fuel System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Confusion; Distraction; Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural MEL / CDL
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: Taxi
Result: General Work Refused
Contributing factors: Aircraft; MEL; Manuals
Primary problem: MEL

Narrative: The MEL for 28-13-01b states to start one engine then shut down the APU. After the first engine start and shutting down the APU the APU SOV OPEN status message remained and threw me off. I started the second engine via cross bleed and completed the pre taxi and taxi checklists. The APU SOV OPEN status message remained after completing the checklists - still throwing me off. I checked QRH Vol. 1 EICAS Message List which listed the message as NA. I read the MEL again which stated 'for an APU fuel feed valve inoperative open' - this seemed to make sense and the First Officer and I discussed that the valve is open and it matches. We decided to continue. Enroute the APU SOV OPEN message was still nagging at me. I reread MEL 28-13-01b again and 28-13-01a for comparison. I referenced the CRJ900 FCOM looking up the APU SOV OPEN status message. The FCOM states the message indicates the APU shut off valve is open with the APU not ready to load. The message typically comes on when the APU is initially energized via the APU PWR/FUEL switch light and goes out when the APU is running and generator operating. After a few moments I came to the conclusion the aircraft is indicating the APU PWR/fuel switch is still energized and providing power to the APU. Upon arrival I decided to shut down the aircraft completely to see if that would reset the aircraft and the message. I didn't expect the APU to start since I was under the impression that the APU has not been shutoff - I did not attempt to start the APU after arrival. After shutting down the aircraft the power up was normal. The APU SOV OPEN message was not displayed until I pressed the APU PWR/fuel switch light and remained on until the APU generator came online which is normal. I stopped the APU pressing the start/stop switch light which brings the message back; waited for the APU door to close and pressed the APU PWR/fuel switch light to de-energize the APU ECU and APU fuel pump and close the APU fuel SOV - nothing happened. This matched my suspicion that the APU remained powered and the fuel SOV is working.I also checked the MCD for current faults; fault history and aircraft history. No APU or fuel system current faults or anything in the fault history for our flight or the flight before; however the aircraft history / fault history page was indicating an open wire/sense for the APU start motor that occurred intermittently 9 times on the flight. The same was also present for the previous flight and the 118 flights before that.I contacted maintenance control and told them my concern that the MEL was incorrect; the MEL was for an inoperative fuel SOV however the SOV was in fact working and it seems the APU PWR/fuel switch is just not responding to being switched off. I also stated the QRH lists the APU SOV OPEN status message as NA which meant two things - 1) there is no MEL applicable to this message and 2) the message is indicating a configuration that is abnormal and is resolved by pilot actions (QRH Vol. 1 ECIAS Message) The maintenance (MX) controller disagreed and stated this was the correct MEL for the message and that the NA means the MEL is the result of another message. The mx controller and I did not agree the aircraft was legal to fly; he stated it was while I contended it was not. The mx controller decided against calling contract mx out to the aircraft and our phone call was ended. I shutdown the aircraft again to see if I could repeat the same events with the same result. I had the same results - the APU PWR/fuel switch did not respond to being pressed to de-energize the APU.  I received a call from the mx control supervisor. I had the same conversation with him that I had with the previous mx controller. After explaining what I was seeing to the supervisor he also reiterated that this was the correct MEL and the aircraft was legal to fly. During our conversation he also stated he doesn't know what fault history message means - it is present on all the aircraft. The phone call ended without resolution.I called crew support to be connected to the flight ops manager. Crew support left a message with the technical manager to call me and the call was ended. I got a call from the pilot policy manager and told him of my concerns. A conference call was initiated with the mx supervisor. During this call the manager tried many times to find a resolution - in the end the mx controller was unwilling to except that the MEL was incorrect; or that a different problem was causing the message to be present; and I wasn't convinced this was the correct MEL. The mx controller was also unwilling to have contract mx come to the aircraft. The call was ended without resolution again. I wrote the aircraft up; indicating the APU PWR/fuel switch was not de-energizing the APU. We swapped into another aircraft for the flight.




Synopsis: A CRJ-900 air crew; after starting one engine and shutting down the APU observed an APU SOV OPEN status message. The message remained on after starting the second engine but they elected to continue and flew one flight. At their destination the Captain troubleshot the aircraft and was convinced that the APU PWR/Fuel switch was inoperative. Maintenance disagreed. The crew swapped into another aircraft for the flight.