Maps used by the crew of Rescue 116 were blurred and contained incorrect details about Blackrock Island.
RTÉ's Prime Time discovered that the height was hidden behind the location code in the helicopter's moving map, while a trial map showed it as 46ft instead of 282ft.
Search and rescue crews had previously complained about poor quality maps.
The investigation also found that there were repeated warnings that the lifejackets were not fit for purpose.
Search and rescue pilot David Abad told Prime Time that the inaccurate map details would have been confusing:
"It is a safety concern. If you don't have an obstacle depicted on the chart, of course, you are flying in not ideal conditions. If you can't rely on the maps you could be in big trouble," he said.