Hersman stressed that while the trainee pilot was flying the plane, the instructor was ultimately responsible, and thus the way they worked together will be scrutinized.
"That's what the airline needs to do, be responsible so that in the cockpit you're matching the best people, especially when you're introducing someone to a new aircraft," former NTSB Chairman James Hall said.
Massachusetts Institute of Technology aeronautics professor Mary Cummings said it's common for two commercial pilots who have never worked together before to be assigned to the same flight.
But she said the military tries to have crews work together more permanently.
"Research would tell you that crew pairing with the same people over longer periods of time is safer," she said. "When two people fly together all the time, you get into a routine that's more efficient. You have experience communicating."
Details emerging from Asiana pilot interviews, cockpit recorders and control-tower communications indicate that Lee Gang-kuk, who was halfway through his certification training for the Boeing 777, and his co-pilot and instructor, Lee Jeong-Min, thought the airliner's speed was being controlled by an autothrottle set for 157 mph.
Inspectors found that the autothrottle had been "armed," or made ready for activation, Hersman said. But investigators are still determining whether it had been engaged. In the last two minutes, there was a lot of use of autopilot and autothrusters, and investigators are going to look into whether pilots made the appropriate commands and if they knew what they were doing, she said.
When the pilots realized the plane was approaching the waterfront runway too low and too slow, they both reached for the throttle. Passengers heard a loud roar as the plane revved up in a last-minute attempt to abort the landing.