Suicide by pilot is an event in which a pilot deliberately crashes or attempts to crash an aircraft as a way to kill himself and sometimes passengers on board or people on the ground. This is sometimes described as a murder-suicide. It is suspected as being a possible cause of the crashes of several commercial flights and is confirmed as the cause in others. Generally, it is difficult for crash investigators to determine the motives of the pilots, since they sometimes act deliberately to turn off recording devices or otherwise hinder future investigations. As a result, pilot suicide can be difficult to prove with certainty.