Regional Jet 900 (CRJ900)
Flight Crew Commercial
Situational Awareness; Confusion
Aircraft Equipment Problem Less Severe
Flight Crew Rejected Takeoff; Flight Crew Returned To Gate; General Maintenance Action
Aircraft
On the takeoff roll; as the pilot flying; just prior to 80 knots both myself and the captain felt a jolt that seemed like a brake had engaged. I was asked if I had my feet on the brakes; to which I responded no. Shortly after the brief discussion we encountered a more pronounced sensation that was longer in duration. At that time the captain assumed control of the airplane an accomplished the rejected takeoff. I contacted tower to advise of the rejected takeoff and; then spoke with the flight attendants to advise of the situation. We then returned to the gate and deplaned normally.
During takeoff roll; the First Officer was the Pilot Flying; there was a slight braking application and I asked the FO if he applied brakes (this occurred at about 80kts; causing me to miss the 80kt call out); about the time he responded no another braking application was felt; this time more severe and for a longer period of time; and the takeoff was aborted. The FO advised the tower and the flight attendants in that order. We then taxied back to the gate and maintenance control was contacted; passengers deplaned normally. This was not a 'text book' abort situation in that there were no aural warnings; no warning or caution messages; and it wasn't obvious that the braking application wasn't pilot induced until discussed. Once it was determined that it wasn't pilot induced and it happened a second time; the decision to abort was made and executed as per the rejected takeoff profile. The First Officer did a great job of communicating with the tower and the flight attendants as time allowed. Maintenance said nothing obvious was broken but they suspected a brake control valve to be the root cause.
CRJ-900 flight crew experiences a possible brake application during takeoff with the First Officer flying; who denies touching the brakes. When a second more vigorus application is felt the Captain rejects the takeoff.