PKPF68-77, the
UK AIP section3, para 3.3 defines icing and notes:
“
It should be noted that the following icing intensity criteria are reporting definitions; they are not necessarily the same as forecasting definitions because reporting definitions are related to aircraft type and to the ice protection equipment installed, and do not involve cloud characteristics. For similar reasons, aircraft icing certification criteria might differ from reporting and/or forecasting criteria.”
Another gap between certification and operational views – opportunity for error.