Date: 201505
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Distraction; Situational Awareness; Time Pressure; Communication Breakdown; Confusion
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Rejected Takeoff; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Gate; Flight Crew Took Evasive Action; General Maintenance Action
Contributing factors: Human Factors; Company Policy; Procedure
Primary problem: Human Factors

Narrative: I was the First Officer and Pilot Monitoring for this flight.  Near the end of our taxi it was a rather busy time due to our starting the second engine followed by the Before Takeoff Check.  As I went off comm to make the departure PA I had the VHF 1 comm button pressed down so I could still hear ATC.  Just before I keyed the mic to make my PA call I heard Tower call us and thought I heard them say; 'XXXX cleared for Take Off runway XX; landing traffic 13 mile final.'  So I went ahead and made my PA telling the passengers '...we are cleared for Take Off; flight attendants please prepare the cabin for departure.'  When I returned to VHF 1 I completed the before takeoff checklist; verified we were entering the correct runway and also verified with the Captain that we were cleared for Take Off which I thought I had heard Tower say and the Captain replied in the affirmative.  We began our Take Off roll and somewhere around 100kts Tower called; 'XXXX you do not have a Take Off clearance!'  I responded; 'You want us to abort?' and Tower replied; 'Affirmative!'  The aircraft reached a max IAS of 115-120kts during the rejected Take Off.  The Captain/Pilot Flying brought the aircraft to a stop and taxied clear of the runway uneventfully.  I ran the table for the Vmbe in the QRH and found our Vmbe = 183 which was well below our Max IAS.  Our Brake Temperature Monitoring System (BTMS) indications did not exceed a 4 on any one brake.  We then contacted Maintenance and had them inspect our brakes and fuse plugs before departure. Both the Captain and I; the First Officer understood we were cleared for Takeoff.  We both heard it on the radio and even verified it with each other.  It was a busy time between checklists and receiving our clearance from ATC.  Since I was still monitoring VHF 1 while making my PA I did not think to question what I thought I had heard.Even if monitoring VHF 1 while off frequency the pilot that was off frequency should still confirm with ATC a Take Off clearance and not just verify it with the other pilot.


Second narrative: After refueling; Maintenance inspection and deplaning some passengers and there bags we departed 87 (?)  minutes late. Late second engine start resulting in single pilot receiving Take Off clearance. Captain headset volume set too low compensating for noise feeding through his hot mike resulting in difficulty clearly hearing clearance. First officer monitoring comm 1 while briefing FA; therefore trying to listen through his own voice.   Both Captain and First Officer believed the flight had been cleared to take off. In debriefing we both thought we had heard cleared for take-off.Captain needs to be less liberal in the use of single engine taxi. Only use it when it is absolutely going to be a delayed/long taxi.Captain needs to manage radio volumes and microphone placement better. Perhaps invest in active noise canceling technology.Captain should reject any take-off clearance if the First Officer is not online to hear it undisturbed.Crew should reconfirm clearance any time one pilot is offline while clearance is given; regardless of how sure crew is about what the clearance was.Switching to tower frequency should not occur until both crewmembers are online and undistracted to ensure no runway related clearance can be heard until both crewmembers are ready to receive it.


Synopsis: A CRJ-700 Captain delayed the engine start during taxi; and while starting it near the Runway's end; the First Officer seated the flight attendants. ATC then cleared the aircraft to line up and wait but as the Captain taxied onto the runway the First Officer; who did not hear line up; began the Takeoff Checklist. The Captain began the takeoff was told to reject around 100kts.