Date: 201311
Local time of day: 1801-2400
Location: TUS.Airport, AZ
Flight conditions: IMC
Light: Night
Aircraft: Regional Jet CL65; Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class C TUS
ATC / advisory: TRACON TUS
Aircraft component: MCP
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Distraction; Fatigue; Human-Machine Interface
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Aircraft Terrain Warning; Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Weather
Primary problem: Human Factors

Narrative: We were proceeding directly to LIPTE intersection maintaining 6;000 feet to join the ILS 11L arrival. At 4 miles prior to LIPTE I (pilot flying) selected HDG mode for the switch to green needles. I inadvertently hit the 1/2 button causing the ILS frequency to disappear in the Comm one standby box. I was distracted by this [and] I tried to fix it. During this time the autopilot disconnected. I was fixated on frequency and did not recognize the autopilot disconnected. The pilot not flying asked what was wrong. I got the right frequency and looked up to see we were low for the approach and the GPWS 'TOO LOW TERRAIN' alert went off. I applied max thrust and started to climb. ATC also said that they were getting a Low Altitude alert as well and suggested 6;000 FT per minute vectoring altitude in that sector. We climbed back through 6;000 FT; leveled off and continued to intercept the ILS 11L and continued inbound on the approach. The day was long with weather in the entire southwest. 5 legs; delayed almost every leg. What was a routine ILS was hampered by fatigue and an inadvertent hitting of the wrong button on the Comm 1 followed by a fixation on the problem. Fatigue being the cause; a solution is to avoid and recognize it before it hampers safety.


Second narrative: We were given direct LIPTE intersection and cleared for the ILS 11L approach. The Captain (pilot flying) switched to heading mode; green needles and I thought approach mode. I then heard the autopilot disconnect; at which point I asked what he was doing - I noticed the FCP wasn't configured for an approach; and I also thought hand flying an approach in IMC; after a 5 leg day where we had experienced delays on every single leg; probably wasn't the best idea when we were both extremely tired. While configuring for the approach; the GPWS went off stating; 'Too Low Terrain'. The Captain immediately initiated a full power climb back to 6;000; our last assigned altitude. Right after that ATC called and informed us that the MVA was 6;000 FT and suggested we return to that altitude; which we already had. We re-engaged the autopilot and executed a normal; safe ILS to landing. The day started off with weather delays; and continued for every single leg. The uncommon weather conditions; turbulence throughout every flight; and long delays most likely contributed to our being fatigued. Upon reflection; it appears that fatigue and fixation on a comm problem was the cause. A solution to fatigue would be to recognize it.


Synopsis: CRJ flight crew reports an inadvertent button push while attempting to select heading on the FCP resulting in autopilot disconnect and the loss of 700 FT. GPWS and ATC both announce the deviation and the Captain returns to 6;000 FT. Both pilots cited a long fatiguing day as contributing to the error.