Originally Posted by
Time Map Ground
En-route descents are NOT required for any abnormal situation. This includes: DP, 1-INOP and Yaw Damper INOP. However, en-route descent planning is required for an 'air conditioning INOP' situation to either FL250 (east) or FL240 (west).
From memory, following a yaw dam failure they always ask you to plan a normal descent to either FL280 or FL290.