I thought that aircraft could use much more than 5%, but that the maintenance regime was different - e.g. [1]. Current engines assume a proportion of impurities and are tuned to work with that, but could be modified to run with 100% SAF if it was available.

Just to add - 10% increase on the state of the art is nothing small!

[1] - https://www.gov.uk/government/news/royal-air-force-completes...