The CAA has published CAP 1519 and 1538 which provide enhanced alerting envelopes for offshore HTAWS. These should go some way to alerting crews on the unsafe conditions which led to accidents at the Cormorant Alpha and ETAP platforms, in Morecambe Bay and on approach to Sumburgh Airport.
Another part of the problem is ensuring that crew “hear” the alerts. Hear is shown in quotations as evidence points to the fact that under some conditions pilots are not aware of the warnings despite them being generated. One example is the near miss to G-WIWI https://assets.publishing.service.gov.uk/media/548aff04ed915d4c100002ce/Sikorsky_S-76C_G-WIWI_12-14_v2.pdf
Recently the CAA has publish CAP 1747, which addresses the Human Factors side of HTAWS and looks at how best to gain the pilots attention when an HTAWS alert is generated.
Unfortunately, the pace of implementing the new envelopes has been slow. In my view, this is largely a result of the poor state of the offshore helicopter industry and their suppliers, which resulted from the shock fall in the oil price in 2014 from $115 per barrel to under $35 per barrel in 2016.
EUROCAE Working Group 110 has started developing Minimum Operation Performance Standards (MOPS) for offshore HTAWS. https://www.eurocae.net/news/posts/2018/october/new-working-group-wg-110-helicopter-terrain-awareness-and-warning-systems-htaws/. The USA's RTCA is joining this effort in June 2019. The MOPS will help by defining internationally agreed standards for offshore HTAWS.