Date: 201602
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Aircraft: A319
Operator: Air Carrier
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Regained Aircraft Control; Flight Crew Rejected Takeoff
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: On takeoff; I set the power initially to 50% N1; then to FLEX. The right engine hung up near idle and did not accelerate to FLEX power; but the left engine did go to FLEX. This pushed the light A319 to the right fairly violently. First Officer (FO) and I pulled the throttles to idle and braked as I attempted to regain directional control and remain on the runway. I over corrected with the steering; but managed to remain on the runway and get the aircraft stopped. We aborted the takeoff at approximately 20 knots and were able to exit the runway in just over 1;000 feet. We evaluated the aircraft for a few minutes; conducted checklists; and made a PA explaining our situation. We then elected to continue with the flight. The second takeoff was normal and the flight [was] uneventful.Closely monitor the engine N1 to ensure the power is stable before moving the throttles to FLEX. Many thanks to the FO for his help in getting the aircraft stopped safely and on the runway.


Second narrative: Upon clearance for takeoff; pilot flying taxied onto the runway and elected to do a rolling takeoff. As we turned the corner; pilot flying advanced throttles from idle power detent straight to flex power without allowing engines to stabilize at 50% as per standard operating procedure. Left engine spooled up quickly to 89% and the right engine lagged significantly at or near idle power. This happened very quickly. I recall yelling out 'the right engine is still at idle' at the same time the aircraft was swerving aggressively towards the unprepared surface on the right side of the runway. I noticed hesitation in the pilot flying to bring the thrust levers back to the idle detent. At this time I reached up as pilot monitoring and grabbed both thrust levers and brought them back to idle detent while simultaneously standing on the brakes. We were able to get the aircraft stopped on the runway and taxi clear. I don't recall the top speed of the aircraft but am confident we never reached a speed more than 20kts. Suggest that during takeoff briefing at the gate prior to push back that the type of takeoff be briefed by the pilot flying (rolling go; standing; etc.); to include the power setting the engines will be stable at before advancing to take off power. I made the assumption that the pilot flying was going to allow the engines to stabilize at 50% as per standard operation procedures; and not advance straight to flex power from idle detent. This event was avoidable. We are fortunate that no one was hurt; the aircraft was not damaged and we were able to keep the aircraft on the prepared surface.


Synopsis: A319 flight crew reported the aircraft swerved toward the runway edge when the engines spooled up at different rates; at least in part because the throttles were advanced without a stabilizing pause at 50% N1 as called for by SOP.