The aircraft's computer system did send about four minutes of automated messages indicating a loss of cabin pressure and an electrical failure, officials have said.
An FBI expert testified at his trial that it would have taken about 30 minutes to build a bomb using materials Mr. Abdo had gathered including a pressure cooker, gunpowder, clocks and electrical tape by following instructions in an al Qaeda magazine found in his backpack.
For the previous several decades, electrical engineers had developed boilers that could withstand enormous and increasing amounts of heat and pressure.