NTSB found that the captain, who hand-flew the takeoff, called for flaps to be reduced from 20 to 5. However the first officer “thought that he heard the captain announce flaps 15.”
The cause of the incident was attributed to “[t]he flight crew’s failure to manage the airplane’s vertical flightpath, airspeed, and pitch attitude following a miscommunication about the captain’s desired flap setting during the initial climb.”