A failure detection apparatus for a hydraulic system , the hydraulic system comprising a tank with hydraulic fluid , a plurality of hydraulically operated devices , a supply line , a pump that delivers the hydraulic fluid from the tank via the supply line to the plurality of hydraulically operated devices , and a case drain line for returning hydraulic fluid from the pump to the tank , wherein the failure detection apparatus comprises: a first pressure sensor configured to sense a first pressure value of the hydraulic fluid in the supply line ; a second pressure sensor configured to sense a second pressure value of the hydraulic fluid in the case drain line ; and a monitoring and failure detection unit configured to receive the first and second pressure values from the first and second pressure sensors and comprises: a monitoring unit configured to monitor first and second pressure values from the first and second pressure sensors during operation of the plurality of hydraulically operated devices , and a failure detection unit configured to memorize Z a plurality of 2-tuples of first and second pressure values , characterised in that the failure detection unit is configured to detect a failure of at least one hydraulically operated device of the plurality of hydraulically operated devices when a 2-tuple of the plurality of 2-tuples is within a first predetermined tolerance range of relative pressure values and outside a second predetermined tolerance range of relative pressure values , and wherein the failure detection unit is configured to detect a failure of the pump when the 2-tuple of the plurality of 2-tuples is outside the first predetermined tolerance range of relative pressure values . a first pressure sensor configured to sense a first pressure value of the hydraulic fluid in the supply line ; a second pressure sensor configured to sense a second pressure value of the hydraulic fluid in the case drain line ; and a monitoring and failure detection unit configured to receive the first and second pressure values from the first and second pressure sensors and comprises: a monitoring unit configured to monitor first and second pressure values from the first and second pressure sensors during operation of the plurality of hydraulically operated devices , and a failure detection unit configured to memorize Z a plurality of 2-tuples of first and second pressure values , characterised in that the failure detection unit is configured to detect a failure of at least one hydraulically operated device of the plurality of hydraulically operated devices when a 2-tuple of the plurality of 2-tuples is within a first predetermined tolerance range of relative pressure values and outside a second predetermined tolerance range of relative pressure values , and wherein the failure detection unit is configured to detect a failure of the pump when the 2-tuple of the plurality of 2-tuples is outside the first predetermined tolerance range of relative pressure values . a monitoring unit configured to monitor first and second pressure values from the first and second pressure sensors during operation of the plurality of hydraulically operated devices , and a failure detection unit configured to memorize Z a plurality of 2-tuples of first and second pressure values , characterised in that the failure detection unit is configured to detect a failure of at least one hydraulically operated device of the plurality of hydraulically operated devices when a 2-tuple of the plurality of 2-tuples is within a first predetermined tolerance range of relative pressure values and outside a second predetermined tolerance range of relative pressure values , and wherein the failure detection unit is configured to detect a failure of the pump when the 2-tuple of the plurality of 2-tuples is outside the first predetermined tolerance range of relative pressure values . <EOS>