49 CFR 835.1: Purpose.

This part prescribes policies and procedures regarding the testimony of employees of the National Transportation Safety Board (Board) in suits or actions for damages and criminal proceedings arising out of transportation accidents when such testimony is in an official capacity and arises out of or is related to accident investigation. The purpose of this part is to ensure that the time of Board employees is used only for official purposes, to avoid embroiling the Board in controversial issues that are not related to its duties, to avoid spending public funds for non-Board purposes, to preserve the impartiality of the Board, and to prohibit the discovery of opinion testimony.