The father of the 20-year-old co-pilot who died along with eight others when their Learjet crashed in Florida said Friday he has listened to his daughter's heartbreaking final radio transmissions "many times" since the crash.

Allan Filgueiras, himself a pilot, was searching for answers as to why the plane plunged from the sky on Sunday - but what he found was immense pride in how his daughter, Nathalia Gadelha Filgueiras, handled the crisis.

"I did listen to that many times trying to find a clue. In my head. How'd that happen? And wow, she's tough," Allan Filgueiras said at a news conference Friday, frequently holding back tears.