The invention relates to a method for detecting a failure of a first turbine engine, referred to as faulty engine (4), of a twin-engine helicopter and for operating a second turbine engine, referred to as sound engine (5), each engine (4, 5) comprising protection end stops regulated by a regulating device which define a maximum power speed, characterized in that it comprises: a step (10) of detecting a fault index of said faulty engine (4); a step (11) of modifying said end stops for protecting said sound engine (5) to protection end stops corresponding to a maximum power single-engine speed, in the event of a fault index being detected; a step (12) of confirming a fault with said faulty engine (4); a step (13) of commanding an increase in the rate of supply of fuel to said sound engine (5) in the event of the fault being confirmed.