Date: 201204
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Rain
Light: Daylight
Aircraft: Regional Jet CL65; Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class C ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Fatigue; Other / Unknown; Communication Breakdown
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: There were no irregular operations or abnormal situations before this incident. The two most important factors were duty day fatigue and the Captain's and mine good working relationship. This was the second day of the Captain and my flying together and third day of the 5 day trip. Our duty day although not long by scheduling standards was 10 hours and the first three days started before 6 am. Our day had 4 flights all under an hour flight time; and the incident was the last [flight of the day]. The longest ground time was 1:46 after the first leg. The whole crew talked during lunch before the flight. The Captain and I discussed that we were tired because of the quick succession of events in [busy] airspace. One key to our error was the familiarity of the Captain's and mine flying styles and personally we are very comfortable with our styles and enjoyed talking about diverse topics outside of the cockpit. During that day I believe we trusted each other and understood the others duties and we shared the decision making and tasks on each flight. Weather only added some workload to the leg with medium build ups and light icing. We briefed and planned an ILS transition to visual outside the FAF. When the time came to lower the gear he asked and I may have responded 'in-transit.' I know I read the landing checklist and the Captain responded normally to the completion of it. The flaps were actually at full and the reversers were both armed. This is when we both noticed the aerodynamic cues of the strange buffet and low power setting which we said might have to do with gust from the heavy rain front approach 15 NM to the west. We were confused by the consistent low power setting and both said something before the gear horn sounded below approximately 1;500 FT AGL. Because of my decreased mental focus I still did not understand what the horn meant for about 5 seconds when the Captain lowered the gear handle himself. The landing check list was finished the second time and the landing was stable from 600 FT AGL to touchdown. I remember that lack of professionalism and breaking sterile cockpit was not a mitigating factor. Please note that when the gear horn sounded my fatigued brain still did not know what the horn meant! I have had two other bad fatigue events. One was driving a car and the other was as an First Officer in 2003. The training on fatigue issues has been thorough enough I could immediately understand the cause and dangers. But; like alcohol effects; there is almost no chance you will recognize you are impaired and then do something about it. More fatigue prevention as a crew will be needed to stop flying as a crew before! The fatigue takes hold and causes errors.




Synopsis: Regional Jet First Officer describes forgetting to extend the landing gear when requested by the Captain; then both pilots missing the gear handle in the up position on the landing checklist. The GPWS sounds to alert the crew and the Captain extends the gear. Fatigue is cited as a factor in the incident.