Pilot Transition
 

Let's say I have 12 helicopter pilots flying single engine turbine VFR. They all have well over 3000 hrs TT and over 100 IFR, plus commercial ratings etc. What is the minimum required training they have to go through to be twin engine rated as well as be qualified to fly a twin engine IFR helicopter? Aside from the minimum they HAVE to do, what SHOULD they go through in your opinion? Thanks!