Narrative:

The controller cleared us for takeoff while the preceding aircraft was still taking off. When writing this report; I listened to a website that archives ATC recordings. The las tower controller cleared the preceding aircraft for takeoff on runway 25R. The controller then cleared us to line up and wait; runway 25R; full length; which I acknowledged. The controller then cleared us for takeoff. I could see that the preceding aircraft was still on the runway; in its takeoff roll; and approximately through only half of its takeoff roll. A jetliner does not start the takeoff roll and lift off in 26 seconds. Seeing this; I refused to accept our takeoff clearance. I quickly decided to not acknowledge our takeoff clearance at all thinking that a comment of 'standby' or something similar could imply a problem of some sort with our aircraft. Therefore; I felt that no acknowledgement was the best course of action; and I did not start the takeoff roll. The controller asked us; 'company flight number; did you copy; cleared for takeoff runway 25R; maintain visual separation with company?' still; the preceding aircraft was on the runway. I delayed my response until I could see the preceding aircraft start rotation. I completed my response; 'company flight number yeah; we copy; cleared for takeoff runway 25R.' by the end of my transmission; the preceding aircraft had rotated. This controller cleared us for takeoff while the preceding aircraft was still on the runway; not once; but twice! It took 48 seconds for the preceding aircraft to start the roll and liftoff; and yet the controller cleared us for takeoff after only 26 seconds (first time) and 37 seconds (second time) had passed in his 48 second takeoff roll! I've seen this occur at las many times before; and the controllers do not effectively manage this hazard; in fact; they cause it. I have had multiple wake turbulence encounters due to las departures being so close to each other as well. I know las tower is under a lot of pressure; but it's clear to me that las controllers often go way outside the envelope (and regulations) to push departures and arrivals to unsafe and/or risky levels.

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Original NASA ASRS Text

Title: Air Carrier departure from LAS expressed concern regarding ATC's use of 'anticipated' separation on successive Air Carrier departure aircraft.

Narrative: The Controller cleared us for takeoff while the preceding aircraft was still taking off. When writing this report; I listened to a website that archives ATC recordings. The LAS Tower Controller cleared the preceding aircraft for takeoff on Runway 25R. The Controller then cleared us to line up and wait; Runway 25R; full length; which I acknowledged. The Controller then cleared us for takeoff. I could see that the preceding aircraft was still on the runway; in its takeoff roll; and approximately through only half of its takeoff roll. A jetliner does not start the takeoff roll and lift off in 26 seconds. Seeing this; I refused to accept our takeoff clearance. I quickly decided to not acknowledge our takeoff clearance at all thinking that a comment of 'standby' or something similar could imply a problem of some sort with our aircraft. Therefore; I felt that no acknowledgement was the best course of action; and I did not start the takeoff roll. The Controller asked us; 'Company Flight Number; did you copy; cleared for takeoff Runway 25R; maintain visual separation with Company?' Still; the preceding aircraft was on the runway. I delayed my response until I could see the preceding aircraft start rotation. I completed my response; 'Company Flight Number yeah; we copy; cleared for takeoff Runway 25R.' By the end of my transmission; the preceding aircraft had rotated. This Controller cleared us for takeoff while the preceding aircraft was still on the runway; not once; but twice! It took 48 seconds for the preceding aircraft to start the roll and liftoff; and yet the Controller cleared us for takeoff after only 26 seconds (first time) and 37 seconds (second time) had passed in his 48 second takeoff roll! I've seen this occur at LAS many times before; and the controllers do not effectively manage this hazard; in fact; they cause it. I have had multiple wake turbulence encounters due to LAS departures being so close to each other as well. I know LAS Tower is under a lot of pressure; but it's clear to me that LAS controllers often go way outside the envelope (and regulations) to push departures and arrivals to unsafe and/or risky levels.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.