For the record, the Hughes 500D or MD500D or whatever you want to call it, is certified under the old Civil Air Regulation 6 and not FAR Part 27.
In the late '70's and early '80's I was doing fully aerobatic routines in the H500D civil and military variants all around the world. The displays were legal because the original certification did not include a "no aerobatic flight" restriction. That restriction came later only because the FAA requested it. The company complied with the request primarily because the FAA took the position that ANY maneuver not conducted during the original certification is not an "approved" maneuver. That interpretation has some huge logical inconsistancies when taken to conclusion, but that is the way it is.
Once that restriction was added we were forced to obtain a special airworthiness certificate with additional inspection requirements and continued certification requirements when returning the aircraft to normal category. Hughes/McDonnell Douglas/Boeing pilots have performed aerobatic displays in the H300C, H500 series, MD520N, and MD900. To my knowledge, we never did any aerobatic displays in the MD600N.
The MD520N was instrumented and tested for aerobatic maneuvers so that it would be certified under Part 27 as an aerobatic capable aircraft but the FAA was unable to define the basic rules for the certification and the request was dropped.
Aerobatic flying is always risky and should always be approached with caution. The approval of authorities in the country where the aircraft and pilot are certified is essential.
Anyone who peforms aerobatic maneuvers at a public or private display without approval should not feel wronged when photographs are published of the aircraft in high angle shots.
"If we complain about the tune, there is no reason to attack the monkey when the organ grinder is present."