Sensors in engines and mechanical components are very common place. The unique piece in the Rolls-Royce new Trent engines is the ability to monitor the performance and standard variance in performance 24/7 even during operation.
Rolls-Royce analysts monitor all engines across airlines and provide reports and maintenance advice to improve the live span of the engine and prevent downtime and incidents. The system leverages the aircraft's standard communication to seamlessly communicate back to base.
Read more about the full work flow here: http://www.rolls-royce.com/about/our-technology/enabling-technologies/engine-health-management.aspx#sense