I thought I'd chime in since I'm the controller in the audio clip. At LAX, we send out a large majority of our clearances via PDC. It's a computer system that allows us to send flight plans directly to an aircraft's ACARS, where the pilots recieve it on a printout, instead of having to read every clearance verbally. At LAX, this saves us a HUGE hassle of reading almost a thousand flight plans a day. Anyways, we got word a couple months ago that some AAL B757-200 series aircraft were outfitted with extra fuel capacity, cause them to fall under the "Heavy" weight-class. So, we no longer send any AAL B757-200 flight plans via PDC because we have to ask each one if they are a Heavy or not. If they are a Heavy, then we go into the system and change the info on their flight plan. If not, then we place a check mark next to their identifier on the flight strip, indicating that it's been verified they're not a Heavy. So when AAL192 approached the runway for departure, I saw that there was no checkmark next to his identifier and that's why I verified if he was a Heavy or not. Hopefully this answers any questions you guys had. -SM