Date: 201601
Local time of day: 0601-1200
Location: LAS.Airport, NV
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower LAS
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Pilot Flying; Captain
Anomaly: ATC Issue All Types
Detector: Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Contributing factors: Company Policy; Procedure
Primary problem: Procedure

Narrative: Cleared for takeoff right behind B757 by LAS tower. Informed LAS tower we need wake turbulence separation behind 757 (per Flight Manual) and tower controller states 'there is no separation behind 757; if you wanted separation you should have told me before taking the runway'. We created our own separation for a very minimum four miles. Takeoff uneventful.


Second narrative: Departing LAS 1R Tower cleared us for 'immediate' takeoff behind a B757. We told him that we required wake turbulence separation to which he said that none was required and that we should have told him that prior to taking the runway. (We were going to delay the 3 B737s behind us that apparently do not require wake turbulence separation). We took our time on the runway for what looked to be safe separation then began our takeoff. Upon arrival at our destination I called the LAS Tower Operations Manager to report what had happened. He stated that they received a revision requiring only visual separation or 3 miles. This conflicts with the FM as well as the stated 'no separation required' by the LAS Tower controller. The next leg it was a repeat of the first leg. Tower controller cleared us for takeoff immediately behind a B757. When we said that we required wake turbulence separation; he said that if we wanted separation that we needed to exit the runway and get back in line. That is what we did. I then asked him about the requirement and he stated that 'none is required with divergent flight paths or 15 degrees'. Divergent or not; we were still following aircraft ahead until crossing the shoreline; a critical time to experience a wake turbulence encounter. I am troubled by the experiences that I have had today with both control Tower's handling this situation. We approach takeoff 'expecting' to be given standard wake turbulence separation and instead were handled as if we made an unrealistic request disturbing the flow. We were literally shamed in front of our peers. My opinion is that there is no standardization across the FAA regarding this issue and my experience today was in direct conflict with the FM.Following this event I searched in depth through the FM; F4 messages; and anywhere else a change to our wake turbulence mins could be hiding and found nothing. For now it seems that the company and ATC are operating with different standards on this topic. Coordination would be helpful as we aircrews should NOT have to call ahead to 'request' separation; it a safety of flight issue.


Synopsis: B737-800 flight crew reported being cleared for takeoff behind a B757 without wake turbulence separation. The Tower is queried and states that the separation standards have been changed. The Flight Manual for the company involved does not reflect those changes.