Originally Posted by
MSPeconomist
Whether someone is entitled to IDB compensation when there is a weight and balance issue depends on the size of the aircraft. In such situations, small planes (i.e., small commuter aircraft or certain xmall RJs) are exempt from the IDB rules, but weight and balance would not be an exemption for mainline service.
As indicated previously indicated and in the wiki, the aircraft exempted are those with a capacity of 60 or fewer. CRJ900 is significantly over that, with a capacity of 79.