Text in force at CS25-28: from CS25-0, effective 17 Oct 2003.
(a) Trim tabs. Trim tabs must be designed to withstand loads arising from all likely combinations of tab setting, primary control position, and aeroplane speed (obtainable without exceeding the flight load conditions prescribed for the aeroplane as a whole), when the effect of the tab is opposed by pilot effort forces up to those specified in CS 25.397 (b).
(b) Balancing tabs. Balancing tabs must be designed for deflections consistent with the primary control surface loading conditions.
(c) Servo tabs. Servo tabs must be designed for deflections consistent with the primary control surface loading conditions obtainable within the pilot manoeuvring effort, considering possible opposition from the trim tabs.
ED Decision 2003/002/RM · Source