Date: 201402
Local time of day: 1801-2400
Location: ATL.Airport, GA
Flight conditions: VMC
Light: Night
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ATL
ATC / advisory: Tower ATL
Aircraft component: FMS/FMC
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Human-Machine Interface
Second reporter function: Captain; Pilot Not Flying
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: The Captain called out Vr and I rotated the aircraft into the command bars. At 'positive rate' I called for 'gear up...speed mode.' It was selected by the Captain. Upon reaching 400 feet AGL; I called for NAV mode and with peripheral vision; witnessed the Captain reach up and select it. My primary focus at that moment was the staying in the command bars and monitoring airspeed and altitude as I called for 'speed 200' and flaps one on schedule. It was at this time that I noticed the aircraft was continuing straight ahead and deviating from the RNAV route that slightly angled north on the moving map. Captain called out 'We're off course' at the same time and I immediately realized the aircraft was in HDG mode and began to turn back on course. After making the correction and during the turn back to the RNAV route; ATC asked if we were RNAV to SNUFY. We confirmed we were in the turn and doing so; however ATC did say he needed us back on track ASAP. I increased the turn and shortly resumed normal navigation. The Captain then selected NAV mode and we never heard anything from ATC other than a frequency change to Departure.After discussing it with the Captain; I believe he accidentally selected HDG mode instead of NAV mode. The previous legs had all been done in HDG mode on departure; and I think he just instinctively selected HDG over NAV. In the future; I will be certain to verify the mode I call for has been selected and is verified.


Second narrative: I would suggest confirming the RNAV departure is armed. Sometimes the FMS starts out in Heading Mode (do to the RNAV departure) with FMS in armed mode and once the airplane gets to the RNAV portion it then engages the FMS NAV. The other change I would suggest would be to put in the initial heading...so that you at least follow the initial heading of the RNAV to prevent ATC deviations with other aircraft. I normally do that but I may have been taken off task by an interruption. For some reason I did not catch the error. I will be more vigilant next time on these critical RNAV departures to confirm the departure; heading and the correct FMS mode.


Synopsis: CRJ-700 flight crew advised by ATC of a track deviation which was caused by Captain accidentally selecting HDG mode rather than NAV mode on RNAV departure.