I am not sure that I can agree with coalface, when he says that chip lights do not give a useful warning. I can think of 2 events where chip lights on Allison engines in JetRangers caused me to land. In both cases, the subsequent engineering investigation grounded the aircraft until the engine was taken out. There was no guarantee that a catastrophic failure would have resulted, but the problems were certainly significant and could have caused an engine failure, and the engineers would not certify the A/C for further flight. In one case we were ferrying a JetRanger from Portugal to the UK, having just picked it up after a purchase. The light came on in Northern Spain, so as per AFM land ASAP. Steel nuggets all over the chip detector and aircraft completed the trip by road.