Righto..... .I was waiting to hear what NIck had to say but here is what I have dredged from the archives. Forgive me if its wrong its been 3 years since flying the C model.. .All the info on the overspeed system is available in the venerable Flight Safety manual. . .. .1. 107% has been addressed on this forum before. To my knowledge it is simply with the retrofit 1S1 the NR needed to be run at 107 rather than retest and all that stuff test pilots do. Ask Nick or go searching around late last year. The aircraft flys really well at 107 due to the reduced pitch angle. Those with the old 'A' commonly increase to 107 for vertical departures and when the blades are not tracking so well, as the reduced pitch reduces the verticals.. .. .2. If I recall correctly, the overspeed system is NOT disabled if one engine is offline. . .. .Many a check pilot will mention that you could consider pulling the O/S CB to prevent a shutdown during OEI. Remember... you didn't hear that from me. <img border="0" title="" alt="[Smile]" src="smile.gif" /> . .. .The reason for 2 probes is to prevent random electrical signals from accidently engaging the OS system ie. magnetic emmissions while flying over high tension power line. The 82.3% N1 limit is extra insurance. . .. .Both probes run at seperate frequencies to avoid this because the entire purpose of the OS is to prevent a condition of excessive turbine RPM launching the blades out of the engine and through the other donk and associated hardware in that area. <img border="0" title="" alt="[Frown]" src="frown.gif" /> Happy thought.... . .. .Additionally on the 1S1 you will see a very heavy steel ring around the turbine area as a practical preventative to this problem. OS may not only be from shaft breaks etc... but also from govenor or FCU runaways.. . <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />