Suicide by aircraft or aircraft-assisted suicide is an aviation event in which a pilot or another person onboard deliberately crashes or attempts to crash an aircraft as an act of suicide, with or without the intention of causing harm to passengers on board or civilians on the ground. If others are killed, it may be considered an act of murder–suicide or mass murder. It is suspected to have been a possible cause in several commercial and private aircraft crashes and has been confirmed as the cause in other instances. Determining a motive can be challenging and sometimes impossible for investigators to conclude especially if the suspected pilot sabotages or disengages their in-flight recorder or in-flight tracker. In the United States, investigations are primarily undertaken by the National Transportation Safety Board and the Federal Bureau of Investigation (FBI).