In the spring of 2023, Robinson fully tested G100UL Avgas. They wrote a report asserting that there were no differences in the performance of their R-44 as compared to 100LL.
Robinson wrote the report and that report has been submitted to the FAA.
Robinson did not follow through with obtaining the timely approval. That is on Robinson.
I have conferred with several rotorcraft DERs and we are fairly confident that we can accomplish a field approval on any Robinson that is supporting emergency services.
Also, piston powered rotorcraft account for about 2% of of all piston powered airplanes.