14 CFR §16.213

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