Flight and Duty Time Limitations (FTL) aim at ensuring that pilot fatigue does not endanger flight safety, i.e. the lives of passengers, crews and the general public underneath the flight paths.
Since the 1944 Chicago Convention, it has been recognised that pilot fatigue (due to long duty hours, insufficient rest/sleep opportunities etc.) can pose a risk to the safety of air operations. This risk needs to be controlled by the means of Flight Time Limitations (FTL) .
1944 Chicago Convention (Annex 6, 9.6.) "The State of the Operator shall establish regulations specifying the limitations applicable to the flight time and flight duty periods for flight crew members. These regulations shall also make provision for adequate rest periods and shall be such as to ensure that fatigue occurring either in a flight or successive flights or accumulated over a period of time due to these and other tasks, does not endanger the safety of a flight."