Chimbu chuckles You are absolutely correct, it was the Schofield Airshow. I do not remember seeing the LR35 do the roll but that is not surprising as I could not even remember the name of the show!
Spaced Hughes, MD and Boeing had a running dogfight with the FAA over the issue of helicopter aerobatics for several years. It would take a very long time to provide you with all the details. The bottom line is that the FAA could never agree what exactly were helicopter aerobatic maneuvers. When the MD520N was being tested for certification, aerobatic maneuvers such as loops, rolls, hammerheads, Split-S and several other maneuvers were flown with the intention of adding them to the certification. The maneuvers were flown during handling qualities and flight strain survey. The FAA could not decide what would be required for certification of those selected maneuvers and the delay in response was holding up final certification of the aircraft so the decision was made to not press the point.
To my knowledge, in over 25 years of aerobatic displays in the 500 series aircraft (I have never flown aerobatics in the MD600N as they have not been tested in that aircraft) I have never had a strap pack laminate break nor has any damage been attributed to maneuvers performed during the show. The aircraft never sees g-loads outside the approved envelope of 3.5 to 0.5 G. Transient power limits are not required. No exceedances have ever been documented. I have held an Airshow Competency Card with no altitude restriction and with series loops and rolls part of the approved sequence.