Date: 201503
Local time of day: 1801-2400
Location: ATL.Airport, GA
Flight conditions: VMC
Light: Night
Aircraft: A300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Climb
Airspace: Class B ATL
ATC / advisory: TRACON A80
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
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 New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: On departure from ATL; we were filed; cleared and flying the CADIT9 RNAV Departure.  Climbing through approximately 4000 feet and after checking on with ATL Departure Control; we were advised radar contact and delete the speed at RBEKA (normally the departure requires MAINTAIN 250 KT until RBEKA).  We acknowledged and deleted the 250 KT speed restriction at RBEKA in the FMC.  Approximately one minute later and climbing through 6000/250 knots; ATC queried us regarding our direction of flight.  We replied we were in the turn to BEDRK from RONII.  The aircraft was in NAV and as it appeared to us; navigating properly with RONII the active waypoint.  However; we did notice the FMC generated route displayed a considerable turn leading RONII to BEDRK.  ATC advised our turn was too early and RONII was still 4 nm ahead.  We were then given instructions to fly an assigned heading before eventually given direct CADIT.  We complied and continued the flight uneventfully.  I believe the deletion of the speed restriction at RBEKA in the FMC may have caused the FMC to over compensate and excessively lead the turn to BEDRK; anticipating an acceleration to 320 kts; although the aircraft was still at 250 kts; as desired.


Second narrative: While flying the CADIT9 RNAV departure out of Atlanta; our FMCs computed a lead turn 4 nm prior to our first waypoint RONII. The FMCs were in High accuracy (1.0) and the autopilot had been engaged in NAV and Profile since 1000 feet agl. The flap retraction was delayed 10 knots as well per procedure and the autothrottles were engaged. The aircraft and procedures were followed precisely. The controller did cancel the 250 knot speed restriction at RBEKA prior to the RONII waypoint. We cleared that speed restriction from the FMC prior to RONII. The controller queried us as the aircraft started turning and we told him that the aircraft was following it's computed lead point and we were turning toward BEDRK; the second waypoint. He said he sees this happen but generally with faster moving aircraft. He gave us a vector and then cleared us direct to CADIT. The rest of the flight was executed normally. No other aircraft were involved and short of intervening with a direct to RONII; I don't know what we should have done differently. All flight procedures were followed correctly.


Synopsis: A300 flight crew departing ATL on the CADIT9 Departure and approaching RONII; is admonished by ATC for an early shallow banked turn to BEDRK. Vectors are issued and the crew explains that the FMC was following its programing; although the early turns normally occur only at higher altitudes and airspeeds.