AV8r. .. .I have no 76 exp but consider this!!. .. .1st case ......drive shaft failure. .. .If you have a driveline failure between the engine and MGB the power turbine will spin to distruction hence N2 overspeed limit at 122% to prevent this. This failure is more likley and hence the need for redundancy ( 2xN2 probes). .. .2nd Case........ .. .possible power turbine failure ie loss of blades on power turbine would reduce the downstream airflow resistance and would result in the compressor overspeeding.. .. .regarding the figure of 82.3% sorry I can't help you there but the limit may not be set by the design of the power turbine but more to do with ancillaries such as starter/Gen etc.. .. .Incomming !!!!!!!!!. . . . <small>[ 22 March 2002, 10:27: Message edited by: MaxNg ]</small>