What are Condition Assessment Scheme (CAS) surveys, and when are they carried out?

MCA Oral Exam Questions

Surveys of oil tankers which complement, and are aligned with, the enhanced surveys under the Enhanced Survey Program, the only significant differences being procedural. 

They are carried out concurrent with intermediate or renewal surveys under the ESP, the first such survey being carried out concurrent with the first scheduled classification intermediate or special survey due after 5 April 2005, or when the ship reaches 15 years of age, whichever is later. A CAS survey includes overall survey, close-up survey, thickness measurements and pressure testing within the cargo area and ballast tanks, including fore and aft peak tanks, of an oil tanker.