Originally Posted by riff_raff
"A TAL could be declared at T+2:30. But neither a Return To Launch Site (RTLS) or TAL could begin until the SRB's were jettisoned. This chart shows the abort conditions for loss of one or more SSMEs."
That chart only applies before the 1986 Challenger accident. Afterward there were many enhancements which enabled intact aborts or at least bailout aborts. For higher-inclination launches (e.g, ISS missions) these also included East Coast Abort Landings (ECAL) at various sites along the U.S. east coast.
The abort improvments can be seen by comparing figure 7 and 8 in the 2011 AIAA document "Space Shuttle Abort Evolution":
http://tinyurl.com/jm8zelv