14 CFR § 16.213 - Discovery.
(a) Discovery is limited to requests for admissions, requests for production of documents, interrogatories, and depositions as authorized by § 16.215.
(1) The information requested is cumulative or repetitious;
(2) The information requested may be obtained from another less burdensome and more convenient source;
(3) The party requesting the information has had ample opportunity to obtain the information through other discovery methods permitted under this section; or
(4) The method or scope of discovery requested by the party is unduly burdensome or expensive.