TSB representative Greg Fife reported tonight that the transponders were turned off for the four A/C in question. It's also possible that with the temperature of the fire inside the rubble of the WTC, he stated that the FDR and CVR may not have survived.
It's extreamly unlikely that the crew were alive at the time of impact for the A/C that struck the WTC and Pentagon. It's likely that they were killed prior to entering the New York city area and the Washington D.C. area. A 911 call was placed from an A/C in-flight phone from the United Airlines 767 that struck the second tower but details have yet to be released.
It's time for Americans to Hold their heads high, mourn those who perished, pick-up the pieces and punish those responsible.
RIP