The abort system ignored the obvious method (the shuttle itself).
IIRC the latest theory is that the crew component of the shuttle went off on a graceful arc before a fatal collision with the sea.
"According to the Kerwin Report:
The findings are inconclusive. The impact of the crew compartment with the ocean surface was so violent that evidence of damage occurring in the seconds which followed the disintegration was masked. Our final conclusions are:
the cause of death of the Challenger astronauts cannot be positively determined;
the forces to which the crew were exposed during Orbiter breakup were probably not sufficient to cause death or serious injury; and
the crew possibly, but not certainly, lost consciousness in the seconds following Orbiter breakup due to in-flight loss of crew module pressure.
Some experts, including one of NASA's lead investigators, Robert Overmyer, believed most if not all of the crew were alive and possibly conscious during the entire descent until impact with the ocean."