Date: 201412
Local time of day: 0601-1200
Location: ONT.Airport, CA
Flight conditions: VMC
Light: Dawn
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ONT
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Fatigue; Communication Breakdown; Confusion; Distraction
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Contributing factors: Human Factors; Procedure; Aircraft
Primary problem: Human Factors

Narrative: After showing on time for a morning departure the crew was delayed with a maintenance item on the airplane. The airplane pushed back about 30 minutes late. All checklists; briefings and tasks were completed normally with the addition of a maintenance procedure that the crew would comply with after departure.The airplane taxied out to the assigned takeoff runway and ran the appropriate pre-departure checklists at the normal time. The crew was given a clearance to 'line up and wait' on the assigned runway; which was read back but miss-interpreted as 'cleared for takeoff' on the assigned runway. The pilot flying (PF) began the takeoff roll and the tower personnel noticed around 80-90 KIAS and issued a confused takeoff clearance. The crew was puzzled by this; believing they had already received the appropriate takeoff clearance and continued the takeoff roll and proceeded to fly the SID and clearance received. About 1500 AGL the tower controller issued the notice of possible pilot deviation and gave a number to call. It was this time that the crew was made available of the possibility of error. The crew called the number upon arrival at destination and was made aware that the deviation had been verified by the audio transcript of the tower/crew interaction.The root cause of this event could have been any number of things. A nonstandard operation was to be conducted after departure in order to comply with a maintenance procedure; fatigue on behalf of the PF could have been a contributing factor; get-home-itis could have been a contributing factor as well as improper Threat and Error management prior to pushback. This event has proved frustrating for me in analysis due to a solid belief that the crew had been issued the appropriate departure clearance and that both crewmembers had believed that clearance to be valid. This event happened at a low workload time for the crew. Neither crewmember was particularly distracted with other tasks at the time; nor was there an apparent loss of situational awareness during the time of the event. Proper verification and cross checking of appropriate takeoff runway and alignment already exist in the SOP; however; individually I plan to incorporate small checks of appropriate takeoff clearance after a 'line-up-and-wait' clearance such as not pressing the TOGA buttons until once the aircraft has received the takeoff clearance in addition to being aligned properly with the runway. On a systemic level; recurrence could be avoided by properly including complacency and rushing as an anticipated threat on the last day of a 4-day trip; especially when taking delays and prior to the holidays.




Synopsis: An aircrew received a 'line up and wait' clearance which was read back but misinterpreted as a 'cleared for takeoff' clearance.