metric - for what it's worth, sounds like the same mod that's available to the 135, a new front door strut that (with a selector) restricts the door from opening fully, acting as a spoiler for the rear sliding door. In the case of the 135, your front door also gets re-inforced down the trailing edge but the overall package allows flight to 110kts, rather than the usual 60kt limit, with the sliding door open.