gulli:
Good explanation. It almost mirrors one I received from a Pratt rep a number of years ago. We were going through a learning curve on our new EC135Ps where they were flying around OEI for various "reasons."
We changed the 1st two engines but on the 3rd they sent a rep and boroscope. A discussion started on the 2.5/30 min OEI which you can see in the downloads.
Long story short... if engine can hang for more than 2.5 why keep the limit. He like me think the 2.5 is a certification "check box" item. But cheaper than wringing out the rest of the system. He mentioned just look at the 139 if you get a little excited on the collective, you change half the M/R limit times.
When I asked the 3 engine divided by 5 mins question he offered to buy the 1st beer. Oh well, maybe next time. Thanks again. W1
And we now return you to your regularly scheduled program on the R44...