Sickle Cell Trait (Haemoglobin AS) is an inherited blood condition, but unlike sickle cell anaemia it is not classified as a disease. It cannot turn into the full blown disease, but can also cause some problems, as there are a percentage of abnormal red blood cells that a carrier has.
There are certain circumstances in which carriers can experience crisis, but it is said to be very rare.
In my experience and from meeting many others like me, who are carriers of sickle cell trait, this is definitely not the case.
I have always had symptoms, some of which have been very severe, from the age of five years old!